WO2006043377A1 - Sheet for forming solder bump and method for manufacture thereof - Google Patents

Abstract

A method for manufacturing a sheet for forming a solder bump which comprises providing a sheet (1) having recesses (5) at prescribed positions, the bottom surface of the recess being comprised of an adhesive (3); filling the recess (5) with a solder powder (6) to thereby attach and hold the solder powder with the adhesive (3); removing the solder powder (6) being not held with the adhesive from the sheet (1); and coating the solder powder in the recess (5) of the sheet (1) with a flux or a thermoplastic resin layer having the function of a flux, to thereby manufacture a sheet for forming a solder bump holding a solder powder in respective recesses. Another method for manufacturing a sheet for forming a solder bump which further comprises heating the above resultant sheet (1), to convert the powder in each dent to one molten sphere (10); and cooling the sheet to form solidified solder balls (11) in respective recesses and thereby manufacture a sheet for forming a solder bump holding solder balls in respective recesses. The above sheet holds solder balls or lots of solder powder in the recesses formed in the sheet, with a loading rate of 100 %.

Description

 Specification

 Solder bump forming sheet and manufacturing method thereof

 Technical field

 The present invention relates to a solder bump forming sheet in which solder balls or solder powder is held in a recess provided on one side of the sheet, and a method for manufacturing the same. This sheet for forming solder bumps is suitable for forming solder bumps on the electrodes of surface mount components.

 Background art

 [0002] A surface mount component (SMD) is an electronic component that is packaged so that it can be directly soldered and mounted on a land formed on the surface of a printed circuit board. Soldering is generally performed by reflow soldering. Is called. The method of mounting printed circuit boards using surface mount components is called surface mount technology (SMT), and has greatly contributed to the recent miniaturization, high performance, high density, and low cost of electronic devices.

 [0003] Among surface-mounted components, QFP (Quad Flat Package), PLCC (Plastic Leaded Chip Carrier), SOP (Small Outline Package), SOJ (Small Outline J-bend package), etc. It has a terminal (lead). When mounting this type of surface mount component on a printed circuit board, solder paste is applied to the land of the printed circuit board, the surface mount component lead is aligned with the land, and the component is mounted on the substrate by the adhesive strength of the solder paste. Then, the printed circuit board is heated in a reflow furnace to melt the solder paste, and solder the surface mount components to the printed circuit board. Such surface-mounted components that have leads on the side of the component cannot greatly increase the number of terminals, and there are restrictions on the increase in functionality.

 [0004] Therefore, at present, BGA (Ball Grid Array), CSP (Chip Size Package), TAB (Tape Automated Bonding), MCM (Multi Chip Module), etc. are arranged in a predetermined pattern on the bottom (or top) of the part. Surface mount components that use smaller solder bumps as terminals and that can be made smaller and more multifunctional have come to be used. Hereinafter, this type of bottom surface terminal type surface-mounted component is sometimes simply referred to as a workpiece.

[0005] BGM, CSP and other bottom surface type surface mount components (workpieces) are mounted on a printed circuit board. This is performed using solder bumps formed as terminals on the bottom surface of the workpiece. Usually, flux is applied to the land of the printed circuit board, and the workpiece is mounted on the land by aligning the solder bump of the work with the land, and the work is held on the board by the adhesive force of the flux. After that, the substrate is heated in a reflow oven to melt the solder bumps on the bottom of the workpiece and solder the workpiece to the printed circuit board.

 [0006] Solder bumps of the workpiece are formed on the electrodes present on the bottom surface of the workpiece. The solder bump is formed by applying an adhesive flux or solder paste to the workpiece electrode and mounting a solder ball on the application part. When a solder ball is heated in a reflow furnace to melt the solder ball, solder bumps are formed on the workpiece electrodes.

 [0007] The conventional workpiece (bottom terminal type SMD) has a 30 x 30mm workpiece substrate with 150 to 250 electrodes, and the pitch between adjacent electrodes is 1.0 to 1.2mm (1000 to 1200 m) It was a wide pitch like this. Therefore, a relatively large solder ball with a diameter of 0.76 mm (760 m) could be used. However, with the further miniaturization of electronic devices, workpieces have become smaller and the solder balls used for the miniaturized workpieces have become smaller. For example, in a workpiece in which 400 electrodes are formed on a 10 x 10 mm workpiece substrate, the pitch between adjacent electrodes is as narrow as 0.5 mm or less. Solder balls used in such narrow pitch forks are of a very small size with a diameter of 0.3 mm (300 μm) or less.

 [0008] In the case of a conventional wide-pitch workpiece, mounting of solder balls on the workpiece has been performed by a suction jig having suction holes at positions corresponding to the workpiece electrodes. After the solder ball is sucked and held in the suction hole of this jig, the jig is moved onto the workpiece and placed in a state where the electrode force is slightly separated. Then, the solder balls are placed on the workpiece electrodes by releasing the solder balls from the jig suction holes by reverse injection.

[0009] If the solder ball is a minute size having a diameter of 0.3 mm or less, various problems arise in mounting the solder ball with a jig having a suction hole. For example, when sucking with a jig, the solder balls are not sucked into all the suction holes. When releasing the solder balls from the jig, the solder balls are clogged with the jig's suction holes and do not come out of the suction holes. If the solder ball is blown off during reverse injection and is not placed on a predetermined electrode, there may be a problem.

 [0010] Therefore, for a narrow-pitch workpiece, hold the solder ball at a predetermined position without using a suction jig! / Use the solder ball placement sheet to place the solder ball on the workpiece electrode. It is done to be installed. The solder ball arrangement sheet has a large number of dents formed at positions corresponding to the workpiece electrodes on one side, and one solder ball is held inside each dent.

 In order to form solder bumps on workpiece electrodes using the solder ball arrangement sheet, solder paste or flux is applied to the workpiece electrodes in advance. After that, the placement sheet is placed on the workpiece with the solder ball holding surface facing downward so that each solder ball faces the workpiece electrode. After that, it is preferable to temporarily fix the solder ball onto the workpiece electrode by heating the placement sheet while heating it to a temperature at which the solder does not melt. In that case, the placement sheet is removed after temporary fixing. Next, the work in which the solder balls are arranged on the electrodes is heated to melt the solder balls. When the solder balls are melted on the workpiece electrodes, solder paste or flux is applied to the electrodes in advance, so that the electrodes are wetted by the molten solder balls and solder bumps are formed on the electrodes. When force is applied without temporary fixing, the placement sheet placed on the workpiece is heated while being pressed, and the placement sheet is removed after the solder bumps are formed.

 [0012] A conventional solder ball arrangement sheet is manufactured separately! It is manufactured by loading minute solder balls one by one in a minute recess of a sheet. Cover the solder balls loaded in the recess with adhesive, cover the sheet surface with a cover film or grease, and place the placed sheet on the workpiece with the solder ball holding surface facing down. This prevents the solder balls from falling off. See JP-A-2-295186, JP-A-8-309523, JP-A-10-51123, JP-A-2003-204144, JP-A-2004-80024, and JP-A-2004-193334.

[0013] However, it takes much time to manufacture the fine solder balls, and it also takes time to load the fine solder balls one by one in the small recesses of the arrangement sheet. Also, the holding force of the solder ball in the recess may not be sufficient. [0014] In general, a fine solder ball is generally manufactured by first producing a linear solder with a very thin diameter, cutting the linear solder into a predetermined length, and then soldering this solder chip into a spherical shape in oil. Is done by doing. However, this method requires a large number of steps as described below.

 [0015] In order to make a small-diameter linear solder, a large solder billet is extruded by an extruder into an intermediate-diameter linear solder, and this intermediate-diameter linear solder is pulled out and passed through a large number of dies by a drawing machine. It requires many time-consuming processes to reduce the diameter. This thin wire solder is cut into a predetermined length with a force cutter to make a solder chip. The obtained solder chip is formed into a solder ball by a ball-in-oil method. In the ball-in-oil method, the solder tip is poured into oil with the upper part at a high temperature and the lower part at a low temperature. At the upper part of the oil, the solder chip melts and becomes spherical due to surface tension, and when it descends into the oil and reaches the lower part of the low temperature, it cools and solidifies into solder balls. Since the solder balls manufactured by the ball-in-oil method have oil on the surface, a cleaning process to remove the oil and a subsequent drying process are required.

 [0016] In order to load the manufactured fine solder balls into the depressions of the arrangement sheet, a large number of the fine solder balls are placed on the sheet, and all of the fine solder balls formed on the sheet are swept with a brush. Put it in the dent. However, when a small solder ball is swept with a brush, the solder ball rolls and the brush force is also separated and scattered. For this reason, it takes a lot of work to obtain a loading rate of 100% in which all the dents are filled with solder balls. In the solder ball arrangement sheet, if there is even one recess that does not contain solder balls, bumps are not formed on all the electrodes of the workpiece, causing defective products.

 [0017] In addition, in the conventional solder ball arrangement sheet, it is actually very difficult to fill only specific recesses with solder balls having a diameter larger or smaller than the others.

 Disclosure of the invention

[0018] The present invention provides a method for producing a sheet for forming solder bumps, in which a solder ball is held in each recess of the sheet, as in the conventional solder ball arrangement sheet. This manufacturing method eliminates the need for both “manufacture of solder balls” and “loading of solder balls into the dents of the sheet”, where V and misalignment are laborious. [0019] The present invention also provides a sheet for forming solder bumps in which solder powder is held in a recess of the sheet and a method for manufacturing the same. This solder bump forming sheet is a force that holds the solder powder in place of the solder balls in the recess of the sheet. Solder bumps are formed on the electrodes of the workpiece by the same operation as the conventional solder ball arrangement sheet. be able to.

 [0020] The present invention further provides a sheet for forming a solder bump, in which a solder ball or solder powder is always present in the depression of the sheet, the loading rate is 100%, and the solder ball or solder powder is held in the depression. A method for reliably and easily manufacturing the device is provided. Therefore, solder bumps can be reliably formed on all the electrodes of the workpiece by using this solder bump forming sheet.

 [0021] The present invention further provides a method for producing a solder bump forming sheet that can easily cope with a case where a part of a work electrode on which a solder bump is formed has a larger or smaller diameter than other electrodes. .

 [0022] The present inventors have found that the solder powder does not scatter when moved with a brush or squeegee, moves in a mountain shape and moves with the brush or squeegee, and is soldered to an adhesive portion having a certain area. When the powder is applied, only the solder powder in the surface layer portion that is in contact with the adhesive portion is attached, that is, a certain amount of solder powder is attached in a planar manner, and the present invention has been achieved.

 [0023] In one aspect, the present invention is a method for producing a sheet for forming solder bumps in which a solder ball or solder powder is held at a predetermined position, including the following steps:

 A. Prepare a sheet having a number of indentations in one position on one side, the bottom side of which also has adhesive strength;

 B. Fill each recess of the sheet with solder powder, and adhere and hold the solder powder with the adhesive on the bottom of the recess;

 C. Hold with adhesive, remove the solder powder from the sheet, and

 D. Cover the solder powder in the recess of the sheet.

[0024] In order to fill the dents of the sheet with the solder powder, a large amount of solder powder is placed on the surface of the sheet on which the dents are formed, and the solder powder is spread by a brush or squeegee. Thereby, the solder powder can be reliably and easily filled in all the recesses. Fill the dent Of the solder powder, the powder adhering to the adhesive on the bottom of the recess is held by the adhesive. Remove any other solder powder in the surplus dent and the solder powder remaining on the sheet surface from the sheet. Excess solder powder can be easily removed by turning the sheet over and tapping it lightly, blowing it with compressed air, or sweeping with a brush.

 [0025] In the first aspect, the method of the present invention produces a solder bump forming sheet in which solder balls are held in a recess of the sheet, similar to a conventional solder ball arrangement sheet. In that case, the method preferably comprises coating the solder powder in the depressions of the sheet with flux in step D above, further comprising the following steps E and F:

 E. Heat the sheet to melt the solder powder in each recess and make the molten solder into one spherical body by surface tension;

 F. Cool the sheet to solidify the spherical molten solder to form a solder ball, and simultaneously hold the solder ball in the recess with the solidified flux.

 [0026] In the second aspect, the above-described steps E and F for forming solder balls are not performed, and a solder bump forming sheet is manufactured in which solder powder is held in a recess formed in a sheet. Even if it is a sheet for forming solder bumps with solder powder attached to the bottom of the sheet recess, it is found that this can be placed facing the workpiece electrode and solder bumps can be formed on the workpiece electrode through heating and crimping. did. In this embodiment, in order to prevent the solder powder from falling off when the sheet is placed on the work electrode and to prevent the oxidization of the solder powder, the solder powder in the recess of the sheet is removed in the above step D. Cover with thermoplastic resin layer or flux. The thermoplastic resin layer preferably exhibits a flux function when melted by heating, and is tack-free at normal temperature! /.

 [0027] In another aspect, the present invention provides a sheet for forming solder bumps produced by the method of the second aspect. This sheet for forming solder bumps has a large number of dents formed at predetermined positions on one side, the bottom surface of each dent is made of an adhesive, and the solder powder attached to the adhesive on the bottom surface is held in each dent. The solder powder is coated with at least one material selected from the group consisting of a thermoplastic resin layer and a flux.

[0028] According to the present invention, the adhesive is held in the depression by the adhesive force that forms the bottom of the depression of the sheet. The amount of solder powder held is approximately proportional to the bottom area of the recess. Therefore, if the bottom area of all the dents formed on the sheet is constant, the amount of solder powder held in the dent will be substantially constant in all the dents, and the solder powder is melted to form a spherical shape with surface tension. The diameter of the resulting solder ball is substantially constant in all the depressions. In this way, it is possible to inexpensively form a solder ball having a uniform diameter in each recess of the sheet without using a solder ball that requires a lot of labor for manufacturing. Furthermore, the solder bumps formed on the workpiece electrodes from the solder balls have substantially the same diameter.

 [0029] In addition, with the solder powder attached to the bottom surface of the recess of the sheet (that is, without forming a solder ball by heating and cooling the sheet), the sheet is placed on the work electrode to which flux has been applied in advance. It can be used as a sheet for forming solder bumps. Also in this case, if the bottom area of all the recesses is the same, approximately the same amount of solder powder is held in the recesses, and the solder bumps formed on the workpiece electrodes by melting of the solder powder in each recess. Also have substantially the same diameter. In this embodiment, since the steps E and F for forming the solder balls can be omitted, the manufacturing cost of the solder bump forming sheet is further reduced.

 [0030] It is not necessary for all the depressions of the sheet to have the same bottom area. Conversely, it is one of the notable advantages of the present invention that a solder bump forming sheet that can form solder bumps of different diameters within the same sheet can be easily realized by changing the bottom area of the recess. .

[0031] Depending on the workpiece, it is necessary to make the diameter of some electrodes smaller or larger than other electrodes. If solder bumps are to be made the same height to ensure connection reliability, the amount of solder supplied on the small-diameter electrode must be reduced. In the present invention, by reducing the bottom area of the depression corresponding to the small-diameter electrode among the depressions of the solder bump forming sheet, the amount of solder supplied onto the small-diameter electrode can be reduced. To meet the demands of When there is an electrode having a larger diameter than other electrodes, the amount of solder supplied onto the electrode can be increased by similarly increasing the bottom area of the recess corresponding to the electrode. Therefore, the present invention can easily cope with the formation of solder bumps having the same height even on workpieces having high-definition electrode patterns having different electrode diameters within the same workpiece. This is extremely difficult with the conventional solder ball mounting method and solder paste method. is there.

 [0032] Further, a solder powder that does not roll with a solder ball that rolls and scatters is filled in the recess of the sheet, and in some cases, a solder ball is formed in the recess by further heating and cooling of the sheet. Therefore, a solder bump forming sheet with a filling rate of 100% in which solder balls or solder powder always exist in the recesses can be reliably produced.

 [0033] Further, inside each recess, the solder ball is held by the solidified flux and the solder powder is held by the thermoplastic resin layer or flux covering the solder ball. For this reason, it is possible to prevent the solder balls or solder powder from dropping off from the sheet during handling or transporting of the solder bump forming sheet. Also, the solder powder is prevented from being oxidized in the recess.

 [0034] When the solder balls or solder powder in the recesses are coated with a flux, this flux performs its function during the formation of the solder bumps. Therefore, it is not necessary to apply the flux to the electrodes of the workpiece forming the solder bumps. However, it is possible to form a solder bump with no voids on the electrode. The same applies when the material covering the solder powder in the recess is a thermoplastic resin layer having a flux function.

 Therefore, according to the present invention, a highly reliable solder bump forming sheet capable of reliably forming good solder bumps having a uniform height on all electrodes of a work can be manufactured at low cost. It becomes possible.

 Brief Description of Drawings

 FIG. 1 (A) to FIG. 1 (F) are explanatory views schematically showing each step of a method for producing a solder bump forming sheet according to the present invention.

 BEST MODE FOR CARRYING OUT THE INVENTION

 [0037] According to the present invention, the solder powder is held by the adhesive force of the adhesive on the bottom surface in each recess of the sheet having the recess composed of the adhesive on the bottom surface at a predetermined position on one side. Then, if necessary, the solder powder is changed to solder balls by heating and cooling the sheet. The position of the recess formed in the sheet can be the same position as the electrode of the workpiece.

[0038] Since the area of the adhesive regulates the amount of solder powder retained in the recess, and thus the volume of the solder bump formed on the electrode, the adhesive is present only on the bottom surface of the recess. Preferably.

 [0039] A sheet having a depression having a bottom surface made of an adhesive on one side is advantageously a multilayer structure having a structure in which a film-like adhesive is sandwiched between a layer having a through hole and a base sheet. Made from sheet. A multilayer sheet suitable for use in the present invention will be described with reference to FIG.

 [0040] The multilayer sheet 1 having a number of depressions 5 according to the electrode position of the workpiece is composed of three layers: a heat-resistant base sheet 2, a film-like adhesive 3, and a resist layer 4 having through holes. Has been. Using the adhesive strength of the film-like adhesive 3, the film-like adhesive 3 is stuck on the heat-resistant substrate sheet 2, and the resist layer 4 is stuck on it. When the multilayer sheet is formed in this way, the through hole of the resist layer 4 becomes a depression 5 and the bottom surface thereof is formed by the adhesive 3. The through hole of the resist layer 4 to be the depression 5 is formed at a predetermined position corresponding to the electrode position of the workpiece.

 [0041] The heat-resistant base sheet 2 is made of a material that does not cause carbonization or deformation at the melting temperature of the solder powder and has heat resistance and does not join the molten solder. Suitable heat-resistant substrate materials are metals such as stainless steel, titanium, and aluminum, and non-metals such as heat-resistant resin and ceramic. The thickness of the heat-resistant substrate sheet 2 is not particularly limited, but 100 to 300 m (0.1 to 0.3 mm) is suitable in consideration of mounting on a workpiece, conveyance, handling, and the like.

 [0042] The film-like pressure-sensitive adhesive 3 sticks and holds the solder powder at the bottom in the recess. As the pressure-sensitive adhesive, any pressure-sensitive adhesive can be used as long as it has a sufficient tack force so that the attached solder powder does not easily fall off. Suitable adhesives include acrylic, silicone and rubber types. The thickness of the film-like pressure-sensitive adhesive 3 is suitably 5 to 10 μm. If it exceeds 10 μm, it may become an obstacle when melting the solder powder or forming solder bumps.

 [0043] The resist layer 4 that forms the depression is a solder resist layer that does not wet the solder, and is preferably formed of a material having both photosensitivity and heat resistance. The resist material can be used in the form of dry film or liquid resist.

[0044] In the first mode in which the solder ball is formed by melting the solder powder in the recess, the thickness of the resist layer 4 is preferably set to be smaller than the diameter of the solder ball to be formed. . More preferably, the solder balls to be formed have a resist layer of 4 to 10 m or more, most The thickness preferably protrudes at a height of 20 / zm or more.

 [0045] In the second mode in which the solder powder in the recess is used as a sheet for forming solder bumps while being adhered and held by the adhesive on the bottom surface, the resist layer 4 has a thickness smaller than the maximum particle size of the adhered solder powder. It is preferable that As a result, the solder powder can surely come into contact with the electrode when the sheet recess is opposed to the electrode of the workpiece and heat-pressed. More preferably, the thickness of the resist layer 4 is 5 m or more smaller than the maximum particle size of the solder powder. If the thickness is larger than that, contact may be uncertain.

 [0046] The through hole of the resist layer 4 can be formed by various methods known in the art. For example, a photolithography method in which a predetermined portion is exposed and developed can be used. In this method, after the multilayer sheet 1 is formed, it is possible to form a hole having a depth penetrating therethrough only in the uppermost resist layer 4. Other methods such as punching, drilling force, and laser processing can also be used. When using these methods, the resist layer 4 does not need to be photosensitive. In these methods, particularly punching and drilling, a through hole is formed in the resist layer 4 in advance before the resist layer 4 is bonded to the film-like adhesive 3. A combination of two or more methods can be used to form the through-hole.

 [0047] As described above, the amount of solder powder adhered and held in the recess is determined by the bottom area of the recess in the sheet. Therefore, the bottom area of the recess is set according to the amount of solder to be supplied onto the workpiece electrode. When the electrode diameters of the workpieces are all the same, it is preferable that the bottom areas of the recesses are all the same. On the other hand, when the workpiece has a high-definition electrode pattern having electrodes of different diameters, the bottom area of the sheet depression can be changed according to the electrode diameter of the electrode pattern.

 [0048] The solder powder used in the present invention may be obtained by appropriately classifying those obtained by an atomizing method, a rotating disk method, a stirring method in oil, or the like. If the mixed state of the powder is uniform, it is not necessary to make the particle size distribution very narrow. However, if the particle size distribution is too wide, there may be a large variation in the particle size of the formed solder balls.

[0049] As the particle size of the solder powder, the larger the number of solder powders adhering to the bottom of the dent, the smaller the variation in the adhering amount. Therefore, the solder powder having a smaller particle size is preferable. In the figure, solder powder is simplified and shown as spherical powder, but it does not have to be spherical powder. The powder may be irregularly shaped.

 [0050] The type of solder powder is not particularly limited. Either a solder alloy powder containing lead or a lead-free solder alloy powder! /.

 Next, one embodiment of the method for producing a solder bump forming sheet of the present invention will be described with reference to the drawings.

 [0051] A. Sheet preparation

 As described above, the sheet 1 is composed of a multilayer sheet in which the resist layer 4 is attached to one side of the heat-resistant substrate sheet 2 via the film-like adhesive 3. The resist layer 4 has a large number of through holes of a predetermined diameter or size at predetermined positions corresponding to the workpiece electrodes on which solder bumps are to be formed, and these through holes form the depressions 5 of the multilayer sheet 1. To do. Since the adhesive 3 is exposed on the bottom surface of the recess 5, the bottom surface of the recess is made of an adhesive. The shape of the through-hole (indentation 5) is usually a cylindrical shape, but may be other shapes such as a prismatic shape (eg, quadrangular prism, hexagonal prism, etc.). The side of dent 5 has a taper!

 [0052] The bottom area of the recess 5 in the sheet 1 determines the amount of solder powder adhered and held in the recess, and thus the diameter of the solder ball on which this solder powder force is also formed. The diameter (more precisely, the area of the bottom surface) of the recess 5 in the sheet 1 (and hence the through-hole of the resist layer 4) may be all the same or may vary depending on the workpiece electrode. The pitch of the recesses 5 should match the electrode pitch of the cake. The diameter of the recess can be, for example, about 60 μm when the electrode pitch of the workpiece is 100 m, and about 120 μm when the electrode pitch is 200 μm.

 [0053] B. Filling with solder powder

 Place a large amount of solder powder 6 on top of the resist layer 4 on the top of the sheet, with the surface of the sheet 1 where the dents 5 are formed on the top, and squeeze the solder powder 6 with the squeegee 7 in the direction of the arrow. Fill the hollow 5 with the powder 6. Since the solder powder does not roll, the solder powder can be easily filled in all the recesses in this way. You can also use a brush instead of a squeegee. Only the solder powder filled in the recess 5 is in contact with the adhesive 3 at the bottom and adheres to the adhesive and is held. If necessary, rock the sheet to ensure that the solder powder adheres to the entire bottom surface of the recess.

[0054] C. Removal of excess solder powder The sheet 1 filled with the solder powder 6 in all the depressions 5 is reversed, and the adhesive powder 3 adheres to the adhesive 3 in the depressions 5 and removes excess solder powder and solder powder remaining on the surface of the sheet 1. To do. This excess solder powder can be removed simply by tapping the inverted sheet 1.

 [0055] As another method, the solder powder can be removed by blowing the compressed air or the like and blowing away the unattached solder powder without turning the sheet upside down. Alternatively, the excess solder powder can be removed by sweeping the inside of the recess with a brush.

 [0056] The solder powder removed in this step and the excess solder powder that has not been filled in step B can be reused in step B.

 D. Solder powder coating

 Indentation 5 and sheet surface force After removing excess solder powder, coat the solder powder 6 in the indentation. The coating material is a solder bump forming sheet that uses the flux in the first embodiment to melt the solder powder in the recesses by heating and cooling the sheet to form solder balls, and without forming the solder balls. In the second embodiment used as a thermoplastic resin layer or flux, it is preferable.

 The coating of the solder powder with the flux in the first embodiment can be performed by applying the flux 9 to the solder powder 6 in the recess 5 with a heat spray fluxer 8. The flux to be used can be selected from those that can be used for soldering electronic components. Either a water-soluble flux or a rosin flux can be used. As shown in the figure, the flux 9 may be applied to the entire upper surface of the sheet 1 (the surface of the resist layer 4) just inside the recess 5, so that the application is easy.

 [0058] The coating of the solder powder with the thermoplastic resin layer or the flux in the second embodiment is useful for preventing the solder powder from falling off in addition to preventing the solder powder from falling off. It is preferable that the thermoplastic resin layer has a flux function. It is convenient in terms of handling and performance that the surface of the thermoplastic resin layer is a tack-free dry film at room temperature.

Preferred [0059] The thermoplastic resin layer is mainly composed of a water-soluble thermoplastic resin and an organic compound containing a hydroxyl group or an ether group. This type of organic compound is This oil layer can serve as a flux. Instead of or in addition to the hydroxyl group- or ether group-containing organic compound, one or more other water-soluble organic compounds can also be used.

[0060] Examples of the water-soluble rosin include polyethylene glycol and derivatives thereof, polyvinyl butyral derivatives, and the like.

 Examples of the organic compound containing a hydroxyl group or an ether group include compounds containing a carboxyl group such as glycolic acid and diglycolic acid, hydroxy-containing amines such as triethanolamine and monoethanolamine, and glycols such as ethylene glycol and propylene glycol. And polyhydric alcohols such as glycerin and trimethylolpropane. The polyhydric alcohol may be one obtained by esterifying some hydroxyl groups with an organic acid.

 [0061] The ratio of the water-soluble rosin to the hydroxyl group or ether group-containing organic compound is not particularly limited as long as a film can be formed. Usually, the hydroxyl group-containing organic compound is 0.1 to 100 parts by mass of the water-soluble rosin. It is the range of ~ 10 mass parts.

 [0062] The coating of the solder powder with the thermoplastic resin layer is performed by applying a resin solution (eg, an aqueous solution or an organic solvent solution) to the solder powder by an appropriate application means such as a spray, and heating it with heat if necessary. This can be done by drying the coating film. Alternatively, it is possible to cover the solder powder in the recess by covering the sheet with a pre-formed resin layer (resin film) so as to cover all the recesses. The thickness of the resin layer is preferably in the range of 0.1 to 10 m.

 [0063] When the solder powder is coated with the flux in the second embodiment, the coating with the flux can be performed in the same manner as described in the first embodiment. After coating the solder powder in the recess with the flux, the solder powder may be heated to a temperature at which the solder powder does not melt to remove volatile substances in the flux and reduce its tackiness.

 [0064] In the second embodiment, a sheet in which the solder powder held in the depression by adhesion to the bottom of the depression is coated with a thermoplastic resin layer or flux is used as a sheet for forming solder bumps.

[0065] On the other hand, in the first embodiment, the solder powder in the recess is preferably coated with a flux. Thereafter, the following steps E and F are further performed to change the solder powder into solder balls.

E. Melting by heating

 The sheet 1 in which the flux 9 is applied to the solder powder 6 in the recess 5 is heated by a heating device such as a reflow furnace to melt the solder powder 6 in the recess 5. At the time of melting, a large number of solder powders 6 present in the respective depressions 5 are removed by the oxides and dirt generated on the surfaces of the individual solder powders by the flux and become a clean surface. Thus, one melt becomes a lump 10. The molten solder lump 10 becomes spherical due to its surface tension.

[0066] Since the fluidity of the flux 9 increases during heating, the flux present on the sheet surface also accumulates at the bottom of the recess 5. Further, the solvent component in the flux evaporates during heating.

 F. Cooling

 The sheet 1 having the molten solder lump 10 spherically formed in the recess 5 is cooled with an appropriate cooling device. The spherical molten solder lump is solidified in the recess 5 and becomes a solder ball 11. At the same time, the flux 9 that has accumulated in the recess and has evaporated the solvent also solidifies. The diameter of the formed solder ball is determined by the amount of solder powder that adheres to the adhesive 3 in Step C and remains at the bottom of the recess 5, that is, the bottom area of the recess 5.

 [0067] Inside each depression 5, the formed solder ball 11 is held by the film-like adhesive 3 present on the bottom surface of the depression 5, but the film-like adhesive deteriorates during heating in step E. Even if the adhesiveness is lost, the solidified flux 9 holds the solder balls 11 firmly. Thus, a solder bump forming sheet is obtained in which the solder balls 11 are held inside the recesses 5.

 [0068] In the solder bump forming sheet of the present invention, whether the solder ball or the solder powder is held in the depression, the depression faces the electrode of the workpiece, as in the conventional solder ball arrangement sheet. As described above, the sheet is placed on the workpiece and heated to melt the solder balls or solder powder in the recesses, thereby forming solder bumps on the electrodes.

[0069] Flux may be applied to the electrode of the workpiece in advance, but the material for coating the solder balls or solder powder in the recesses is a flux or a thermoplastic resin layer having a flux function. In this case, flux application to the electrode can be omitted. heating Is preferably performed while pressure is applied to the sheet. A preferred pressure is in the range of 0.01 to 0.1 N per electrode. The formed solder bump has a diameter corresponding to the amount of solder powder held in the recess. When the flux or thermoplastic resin layer is water-soluble, the workpiece is finally washed with water to remove the remaining flux or resin layer.

 Example 1

 [0070] This example illustrates the production of a sheet for forming solder bumps according to the first embodiment in which solder balls are held in the respective recesses by the steps of FIGS. 1 (A) to (F). The work for forming solder bumps with this solder bump forming sheet had 3600 electrodes at a pitch of 200 (0.2 mm).

 [0071] Acrylic film adhesive (10 μm thick) is pasted on one side of a 200 μm-thick stainless steel sheet to be a heat-resistant substrate sheet, and a 25 μm-thick dry film is further formed thereon. A4 (multi-layer sheet) was prepared by laminating a solder resist (Raytec SR-FZ, manufactured by Hitachi Chemical Co., Ltd.).

 [0072] A recess having a diameter of 120 / zm that penetrates completely through the resist layer is formed in the uppermost resist layer of the formed multilayer sheet by a lithography method including exposure and development through a mask. By forming 3600 pieces with a 200 μm pitch for one workpiece in accordance with the electrode pitch of the workpiece, a multilayer sheet having a plurality of depressions for the workpiece was obtained. The adhesive was exposed on the bottom surface of each formed depression.

 [0073] Next, a solder powder (Sn-3Ag-0.5Cu, melting point 217 ° C) having a particle size of 25 to 36 μm is placed on the surface of the resist layer of the multilayer sheet, and all of them are ground with a squeegee. The hollow was filled with solder powder. Thereafter, by blowing compressed air onto the sheet, all of the excess solder powder remaining in the recesses and on the sheet surface and not adhering to the adhesive was removed from the sheet.

Next, a water-soluble flux was applied to the sheet surface with a spray fluxer, and the solder powder in the recess was covered with the flux. This sheet was then heated to a temperature at which the solder powder melts in a reflow oven in a nitrogen atmosphere. Due to the heating in the reflow furnace, the molten solder powders were united in each recess to form one spherical molten solder lump. After that, when the sheet is cooled to room temperature with a cooling device attached to a reflow furnace and the solder lump is solidified, a solder ball having a solder ball with a diameter of 60 ± 3 m is present inside all the depressions. An amplifier forming sheet was obtained.

 [0075] This solder bowlet protrudes about 35 μm from the resist surface, and when the sheet is placed on the workpiece surface, the solder ball is sufficiently protruding so that the solder balls in the recess come into contact with the workpiece electrode. . In addition, the solder balls in each recess were firmly held by the flux solidified in the recess, and the solder balls did not fall out of the recess even when the sheet was turned upside down.

 [0076] A sheet for one work piece is cut out from the obtained solder bump forming sheet, placed on the work piece so that the solder ball of the sheet faces the work electrode, and a pressure of 100 to Uton is applied to the sheet. When applying heat and pressure for 30 seconds at a set temperature of 230 ° C., good solder bumps were formed on all 3600 electrodes of the workpiece. At this time, the solder balls were held in the dents where the flux was applied to the workpiece electrode, and the flux was melted to clean the electrodes and clean soldering was possible. When the solder bump joints were examined by X-ray transmission, no voids were observed.

 Example 2

 [0077] This example illustrates the production of the solder bump forming sheet according to the second embodiment in which the solder powder is adhered and held in each recess by the steps of FIGS. 1 (A) to (D). The work for forming solder bumps with this solder bump forming sheet had 3600 electrodes at a pitch of 200 (0.2 mm).

 [0078] In the same manner as described in Example 1, a recess having a diameter of 120 m is formed in the electrode pitch of the workpiece in a multi-layer sheet of A4 size that also has a three-layer force of a base material, an adhesive, and a resist layer. In total, 3600 sheets were formed at a pitch of 200 m per square, and a multilayer sheet with multiple workpiece depressions was obtained.

 [0079] Next, a solder powder (Sn-3Ag-0.5Cu, melting point 217 ° C) having a particle size of 25 to 36 μm is placed on the surface of the resist layer of the sheet, and is ground with a squeegee to form all the depressions Filled with solder powder. Thereafter, excess solder powder that did not adhere to the recess was swept away with a brush and removed.

[0080] Next, an aqueous coating composition mainly composed of polyethylene glycol-based water-soluble thermoplastic rosin and dallic acid (amount of 5 parts by mass with respect to 100 parts by mass of rosin) on the surface of the sheet. By spray-coating the product to form a film with a thickness of about 5 m, the solder powder in the depression was covered with a resin layer. The surface of the film after drying was tack-free and easy to handle with no stickiness. Thus, a solder bump forming sheet in which solder powder was adhered and held in all the depressions of the sheet was obtained.

 [0081] A sheet for one work piece was cut out from the obtained solder bump forming sheet, placed on the work piece so that the solder ball of the sheet faced the work electrode, and the pressure of 100 to Uton was applied to the sheet. When applying heat and pressure for 30 seconds at a set temperature of 230 ° C., good solder bumps were formed on all 3600 electrodes of the workpiece. At this time, the solder powder was held in the recess of the force applied by applying flux to the workpiece electrode, and the soldering function was performed by the flux function exhibited by the resin layer. When the solder bump joints were examined by X-ray transmission, no voids were observed.

 [0082] The method of the present invention is suitable for the manufacture of a solder bump forming sheet in which a minute solder ball having a diameter of 300 μm or less or a corresponding amount of solder powder is held in each recess, but has a larger diameter. It is also possible to manufacture a solder bump forming sheet in which each solder ball or an equivalent amount of solder powder is held in each recess. In addition, the diameter of the solder balls or the amount of solder powder held in the same sheet can be easily changed for each depression.

 [0083] The use of the solder bump forming sheet of the present invention is not limited to the formation of solder bumps on the electrodes of surface mount components such as BGA and CSP. For example, it can be applied to other applications in which solder balls are mounted in place or solder bumps are formed.

Claims

The scope of the claims  [1] A method for manufacturing a solder bump forming sheet that holds solder balls or solder powder in place, including the following steps:  A. Prepare a sheet having a number of indentations in one position on one side, the bottom side of which also has adhesive strength;  B. Fill each recess of the sheet with solder powder, and adhere and hold the solder powder with the adhesive on the bottom of the recess;  C. Hold with adhesive, remove the solder powder from the sheet, and  D. Cover the solder powder in the recess of the sheet.  [2] A method for producing a solder bump forming sheet with solder balls held in place, including the following steps:  A. Prepare a sheet having a number of indentations in one position on one side, the bottom side of which also has adhesive strength;  B. Fill each recess of the sheet with solder powder, and adhere and hold the solder powder with the adhesive on the bottom of the recess;  C. Hold the adhesive, remove the solder powder from the sheet,  D. Cover the solder powder in the recess of the sheet with flux,  E. Heat the sheet to melt the solder powder in each depression, and make the molten solder into one sphere by surface tension; and  F. Cool the sheet to solidify the spherical molten solder to form a solder ball, and simultaneously hold the solder ball in the recess with the solidified flux.  [3] Manufacturing method of solder bump forming sheet holding solder powder in place, including the following steps:  A. Prepare a sheet having a number of indentations in one position on one side, the bottom side of which also has adhesive strength;  B. Fill each recess of the sheet with solder powder, and adhere and hold the solder powder with the adhesive on the bottom of the recess; C. Hold with adhesive, remove the solder powder from the sheet, and D. Cover the solder powder in the recess of the sheet with at least one material selected from the group consisting of a thermoplastic resin layer and a flux. [4] In step A, the sheet prepared in step A is a composite in which a solder resist layer having a large number of through holes at a predetermined position is laminated on a heat-resistant substrate sheet via a film-like adhesive. 4. The method according to any one of claims 1 to 3, which is a layer sheet. [5] The bottom areas of all the recesses of the sheet prepared in step A are substantially the same, so that in step D, the amount of solder powder in the recesses of the sheet is substantially the same in all recesses. The method according to any one of claims 1 to 3, wherein: [6] The method according to any one of claims 1 to 3, wherein the sheet prepared in step A has depressions having different bottom areas, whereby the amount of solder powder in the depression of the sheet varies in step D. .  [7] It has a number of depressions formed at predetermined positions on one side, and the bottom surface of each depression is composed of an adhesive, and solder powder attached to the adhesive on the bottom is held in each depression, and A solder bump forming sheet, wherein the solder powder is coated with at least one material selected from the group consisting of a thermoplastic resin layer and a flux.  [8] The solder bump forming sheet according to [7], wherein the thermoplastic resin layer can exhibit a flux function when heated and melted and is tack-free at room temperature.  [9] The solder bump forming sheet according to claim 8, wherein the thermoplastic resin layer is composed mainly of a water-soluble thermoplastic resin and an organic compound containing a hydroxyl group or an ether group.