US2970064A - Masking material particularly for gas plating processes - Google Patents

Description

Jan. 31, 1961 w. M. BOLTON 2,970,064

MASKING MATERIAL PARTICULARLY FOR GAS PLATING PROCESSES Filed May 15, 1957 FIG. I

7 7 r1 II II II w ll I! II IN VEN TOR. W/LBUR M. BOLTON ATTORNEYS United States Patent 9 MASKING MATERIAL PARTICULARLY FOR'GAS PLATING PROCESSES M. Bolton, Piqua, Ohio, assignor, by mesne assignrneiits; to Union Carbide COT'POI'QUOHyNGW York, N.Y., a corporation of New York Filed May 13, 1957, Ser. No. 658,568

4 Claims. (Cll 117-55) 1 This invention relates to the metallizing of materials by"n'iear'is"-of'depos'ition of metal from the gaseous state is particularly concerned with the masking off of selected areas of a substrate to inhibit metallic deposition' thereon; further, the invention is specifically conclei'ned w'ith'masking agents which not only inhibit the nietallic deposition but which are readily removed from a substrate after completion'of metallizing and which provide a's'harp' line of demarcation between a metalliaed and a non-metallized area.

he invention has been found to be of considerable utility inIthe productionof printedcircuits wherein an electrically" conductive film of metal of relatively narrow u'fidth'and frequently serpentine configuration is provided oii'a substrate of insulating materiaL'such as a board of zf'phenolic' resin, for exam le.

li ac-c rdance with thisinvention a masking agent wlilehexhibits particular utility in gas plating applicatitiiisf, including the plating of printed circuits, comprises afilmfformer and a vehicle of low volatility. With such cfonib ination it appears that in the course of gas plating the ve'hicleis slowly released from the filmand'crea'tes over the film avapor pressure of the vehicle which inhibits deposition -of the metal from the gaseous'constituent on the film. With such deposition inhibitor present d efpos'itior' may be substantially completely prevented or'ifit does'oc'cur, the deposition is of such adiscontinuotis nature or is soslight that penetration of the film bit' a subsequently applied washing liquid is" not preven a; I

Theffilm itself is preferably of such a nature that it may be removed, with anyresidual vehicle therein, from th substrate" without damage to the substrate by' corn in I washing-liquids, such as water, soap solutions; water and" alcohol solutions, and similar materials.

I";hayefound that film formers which are not reactive with the vehicle to produce material'sinsoluble in comtrion w'ashing liquids'are particularly effective; such film formers also are suitably water-soluble or water disp'ei-fsibl'e and are'not rendered insoluble by moderate tem pei'atures up to 400-500 F. Particularly etfective for the pr'a'ctice of the invention are film formers such as plant; vegetable and bacteriological gums; for example,

aesaraat; celluloses such as carboxy methyl cellulose,

and alginates are useful. i

The vehicle for combination with the film former is suitably a polyhydroxy aliphatic, such as glycerin, ethylene glycol, propylene glycol and high analogues, and also including'theglycol ethers and mixed ethers, for example; butycarbitol is a useful ether.

For ease of practice of the invention I have found that'avehicle whichis readily miscible with water, that is gly'cerine, is to'b e preferred; Glycerine is readily retained by film formers such as dextran at normal temtui'e'sat sucha rate as to admirably perform the neces deposition-inhibitingfunction; In combination withice 2. dextran and water glycerine forms a convenient dispersion for film forming.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings in which:

Figure l is a schematic view illustrating apparatus useful in the practice of the invention;

Figure 2 is a plan'view of a board of insulating material masked ofi for the formation of a printed circuit utilizingthe apparatus of Figure 1;

Figure 3 is an enlarged and sectional view of the board' of Figure 2 taken substantially on line 3-3 of Figure 2;

Figure 4 represents thestructure of Figures 2 and 3 in the course of the metallizing operation indicating sche matically the vaporization of vehicle from the'masking film;

Figure 5 is a view similar to that of Figure 3 after metallizing and-before removal of the masking agent; and

Figure 6 is a plan view of the product of the operation in full scale and after removal of the masking agent.

Referring to the drawings and initially particularly to Figure 2 the numeral 1 designates a thin rectangular board of electric'al'insulating material such as a phenolic resin base board. Coated on the board 1 and outlininga configuration 3lfor a printed circuit which is to include terminals as at 5 is a masking agent 7 produced in accordance with the principles of this invention.

An excellent masking agent comprises as the filmformer, dextran a high molecular weight gum glycerinas the vehicle of 10w volatility, and water as the dispersing agent; While the water content mayvarywith the molecular weight of the gum andmay be varied to aid ready disp er sibility a convenient formula well suited" to the purpose has been found to be approximately equal weights of glycerin and dextran together with water to the'extent of'about'IO'times the dextran weight; Thus a formula employing 10 grams of dextran (M.W. approx. 1,000,000), 10 gramsof glycerin' and cc. of water has been employed The board 1 prior to coating should 'be cleaned of oil or grease chemically and suitably the board is also roughened by sand-blasting or with a 320 grit emery. v The dispersion is spread on the cleaned board 1 in any convenient manner to form the film and to outline the" and'then a secondcoat is applied and dried at the same temperature. Such is a most suitable procedure for the;

specific formulation noted above. The drying in each instance shouldtake place until the exposed surface of the film is just tacky.

The board with the film formed thereon is then placedin the apparatus of Figure 1, for example, where it is exposed to an atmosphere of a plating gas; such may suitably' be nickel carbonyl and the temperature of the board within the chamber is then brought up to 285 to 290 F. as will be noted hereinafter in connection with the specific description of the apparatus.

As the board 1 and film 7 are heated glycerin slowly;

evolves as indicated at 9 in Figure 4 and-a vapor pressure of glycerin exists over the masked areas. This vaporpressure tends to prevent deposition of the metal of theni'ckel carbonyl on the masked areas but does not prepent the build-up of nickel in the unmasked areas as-at 11 (Figures 3, 4 and 5').

I With the masking agent specifically referred .to'above an exposure time of ten minutes to the plating'gas has Patented Jan. 31, 1961 which is desirable in aiding the final-washing. The wash-- ing may be effected with plain water and such is generally preferable; however, as already noted, was liquids which do not affect the insulating board 1 or the deposit of metal may be employed.

The masking agent is completely removable and it leaves a finely delineated circuit configuration (Figure 6). Referring now more particularly to the exemplary apparatus illustrated in Figure 1, the numeral 13 designates a vaporizing chamber, while the numeral 15 indicates a conduit extending into the chamber, terminating in a nozzle 17. and which is adapted for the flow of nickel carbonyl to the chamber from a suitable source of liquid carbonyl indicated at 19.

Leftwardly in Figure 1 the numeral 21 designates a conduit which is connected to a source of helium, while the numeral 23 designates a conduit which is connected to a source of anhydrous ammonium gas. Valves 25, 27 are provided in the respective conduits for the control of gas fiow.

The helium and ammonia mix together in the conduit 29 and flow to the chamber 13, where they mix and serve as a carrier for the nickel carbonyl gas formed by the flash vaporizing of the liquid nickel carbonyl. This plating gas then passes through conduit 31 to the plating chamber 33 which, in its lower portion, is provided with a platen 35 adapted to be heated electrically through leads 37, 39. As indicated in Figure 1 the insulating board 1 is placed on and heated from the platen 35.

Gases are exhausted from the plating chamber 33 through conduits as at 41, 43, 45. These exhaust gases may suitably be flowed to a burner or to a recovery apparatus as desired.

In connection with the plating operation it is desirable that the plating chamber be of sufficient size, such that no build-up of pressure of the vehicle will occur over the areas which are to be metallized. This is not a critical matter and obviously the volume should be such that no material amount of glycerin, for example, exists in the vapor pressure within the plating chamber, the primary vapor pressure of the vehicle existing only at the masked area as it emanates from the masking film.

When dextran is used as the film former, glycerin may be present to the extent of about percent of the weight of the dextran, or glycerin may be present in considerable excess, for example, ten times that of the weight of the dextran.

Similar considerations apply to the use of the other film forming agents with respect to proportions. However, as already noted, it is preferable that the glycerin be present in the masking agent to such an extent that under the conditions in which it is to be employed, some glycerin will remain in the film after the completion of the metallizing operation.

In some instances some slight deposition of metal has occurred on the masking agent, but in every case this deposition has been in such a state that it is readily permeable by water, and no difliculty has beenlexperienced in removing the films with water alone, although the speed of this operation may be increased by employing a slight alkali, such as a soap solution. Also, if desired, an alcohol-water mixture to the extent of about 50 percent alcohol, may be employed.

The success of this method of plating is attributed to the non-coherency of any metal deposit which occurs on the masking film, thus providing for the penetration of water, while the metal deposit itself which forms the conduction portion of the printed circuit is highly coherent.

While large amounts of glycerin are employable, it is preferable to operate on the side of the minimum of vapor pressure, and hence a small amount of glycerin, in order to avoid the formation of slight halos which tend to prevent sharp delineation of the metal deposits.

Accordingly, while the vehicle should be present in sufficient extent to havesome glycerin remaining in the film at the end of the operation, it should not be present to such an extent that undue halo formation occurs; When the amount of glycerin exceeds the proportions set out in the ranges given hereinbefore, such halo formation may occur and affects the appearance of the article but does not deleteriously affect the utility.

It will be understood that this invention is susceptible to modification in order to adapt it to difierent usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. A process for the production of well delineated metallic deposits covering only a surface portion of an object which comprises applying to the object a masking agent to delineate on the object the contour of the deposit to be formed, said masking agent comprising a film former consisting of a viscous mass composed of dextran and a glycol vehicle releasable from the film former at temperatures below 500' F., said film former being water dispersible and capable of retaining its water dispersibility when subjected to heat, heating the object in an enclosed vessel to a temperature sufficiently high to decompose a metal-bearing heat decomposable gaseous compound and less than 500 F. to induce volatilization of the vehicle and to create a vapor pressure of the vehicle over the masking agent, passing a heat-decomposable gaseous compound which is decomposable at temperatures above 75 F. and below 500 F. to the object to be plated while the object is maintained at decomposition temperature and while said vehicle is being volatilized to thereby deposit on the delineated portion of the object metal while the deposition of metal on the masking agent is inhibited, removing the object from the vessel, and thereafter washing the masking agent from the object.

2. A process for the production of well delineated metallic deposits covering only a surface portion of an object which comprises applying to the object a masking agent to delineate on the object the contour of the deposit to be formed, said masking agent comprising a film former consisting of a viscous mass composed of dextran and glycerine, heating the object in an enclosed vessel to a temperature sufficiently high to decompose a metalbearing heat-decomposable gaseous compound but to less than 500 F. to induce volatilization of the glycerine and to create a vapor pressure of the vehicle over the masking agent, passing a said heat-decomposable gaseous compound to the object to be plated while the object is maintained at said decomposition temperature and while said vehicle is being volatilized to thereby deposit on the delineated portion of the object metal while the deposition of metal on the masking agent is inhibited, continuing the deposition to produce a desired plating thickness, removing the object from the vessel while some glycerine remains in the masking agent, and thereafter washing the masking agent from the object.

3. A process for the production of well delineated metallic deposits covering only a surface portion of an object which comprises applying to the object a maskng agent to delineate on the object the contour of the deposit to be formed, said masking agent comprising a film former consisting of a viscous mass composed of dextran, glycerine and water, preparing the masking agent by heating a film thereof on the object to drive off water until the film is just tacky, heating the object in an enclosed.

vessel to a temperature sufficiently high to decompose a metal-bearing heat-decomposable gaseous compound toto be plated while the object is maintained at said decomposition temperature and while said vehicle is being volatilized to thereby deposit on the delineated portion of the object metal while the deposition of metal on the masking agent is inhibited, continuing the deposition to produce a desired plating thickness, removing the object from the vessel while some glycerine remains in the masking agent, and thereafter washing the masking agent from the object.

4. A process for the production of well delineated metallic deposits covering only a surface portion of an object which comprises applying to the object a masking agent to delineate on the object the contour of the deposit to be formed, said masking agent comprising a film former consisting of a viscous mass made up of d'extran and glycerine the same being in approximately equal amounts by weight dextran and glycerine, heating the object in an enclosed vessel to a temperature sufliciently high to decompose a metal-bearing heat-decompossble gaseous compound to induce volatilization of the glycerine and to create a vapor pressure of the vehicle over the masking agent, passing a said heat-decomposable gaseous compound to the object to be plated while the object is maintained at said decomposition temperature and while said vehicle is being volatilized to thereby deposit on the 6 delineated portion of the object metal while the deposition of metal on the masking agent is inhibited, While glycerine is retained in the masking agent removing the object from the vessel, and thereafter washing the masking agent from the object.

References Cited in the file of this patent UNITED STATES PATENTS 1,656,265 Cosner Jan. 17, 1928 2,139,640 Mall Dec. 6, 1938 2,306,887 Klose Dec. 29, 1942 2,484,019 Devores Oct. 11, 1949 2,602,755 Silvermail July 8, 1952 2,653,108 Oakley Sept. 22, 1953 2,668,120 Leaf et a1. Feb. 2, 1954 2,674,584 Deniston Apr. 6, 1954 2,716,615 Voris Aug. 30, 1955 2,736,710 Nack et a1. Feb. 28, 1956 2,835,603 Swinehart et al May 20, 1958 2,847,330 Toulmin Aug. 12, 1958 OTHER REFERENCES Printed Circuit Technique, National Bureau of Standards Circular 468, issued Nov. 15, 1947, pages 25 and 26.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF WELL DELINEATED METALLIC DEPOSITS COVERING ONLY A SURFACE PORTION OF AN OBJECT WHICH COMPRISES APPLYING TO THE OBJECT A MASKING AGENT TO DELINEATE ON THE OBJECT THE CONTOUR OF THE DEPOSIT TO BE FORMED, SAID MASKING AGENT COMPRISING A FILM FORMER CONSISTING OF A VISCOUS MASS COMPOSED OF DEXTRAN AND A GLYCOL VEHICLE RELEASABLE FROM THE FILM FORMER AT TEMPERATURES BELOW 500*F., SAID FILM FORMER BEING WATER DISPERSIBLE AND CAPABLE OF RETAINING ITS WATER DISPERSIBILITY WHEN SUBJECT TO HEAT, HEATING THE OBJECT IN AN ENCLOSED VESSEL TO A TEMPERATURE SUFFICIENTLY HIGH TO DECOMPOSE A METAL-BEARING HEAT DECOMPOSABLE GASEOUS COMPOUND AND LESS THEN 500* F. TO INDUCE VOLATILIZATION OF THE VEHICLE AND TO CREATE A VAPOR PRESSURE OF THE VEHICLE OVER THE MASKING AGENT, PASSING A HEAT-DECOMPOSABLE GASEOUS COMPOUND WHICH IS DECOMPOSABLE AT TEMPERATURES ABOVE 75*F. AND BELOW 500*F. TO THE OBJECT TO BE PLATED WHILE THE OBJECT IS MAINTAINED AT DECOMPOSITION TEMPERATURE AND WHILE SAID VEHICLE IS BEING VOLATILIZED TO THEREBY DEPOSIT ON THE DELINEATED PORTION OF THE OBJECT METAL WHILE THE DEPOSITION OF METAL ON THE MASKING AGENT IS INHIBITIED, REMOVING THE OBJECT FROM THE VESSEL, AND THEREAFTER WASHING THE MASKING AGENT FROM THE OBJECT.

Images