JP2007033194A - TEST BOARD AND JOINT STRESS MEASUREMENT METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a test substrate and a stress measuring method capable of measuring accurately a stress caused by drop impact applied to a joint between an electronic component and a substrate. <P>SOLUTION: This test substrate 1 is equipped with the substrate 2, the first electrode 9 provided on the substrate 2 surface, a piezoelectric element 10 laminated on the first electrode 9, the second electrode 11 laminated on the piezoelectric element 10, the first external terminal 5 provided on the substrate 2 and connected to the first electrode 9, and the second external terminal 6 provided on the substrate 2 and connected to the second electrode 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a test substrate and a stress measurement method for a joint, and more particularly to a test substrate used for measuring an impact stress of a joint between an electronic component and a circuit board in a drop impact test of an electronic component mounting device, and the test substrate. The present invention relates to a method for measuring stress at a joint portion.

  In a drop impact test method for electronic component mounting devices in which electronic components such as ICs, LSIs, resistor elements, and capacitor elements are soldered to a substrate, how much impact can be maintained in the solder joint until the solder joint is subjected to impact There is known a method described in Non-Patent Document 1 below that quantitatively represents the reliability of the solder joints against dropping.

In the method described in Non-Patent Document 1, an electronic component is solder-bonded to a substrate, and an evaluation sample in which a strain gauge is attached to the back side of the solder-bonded portion of the electronic component on the substrate is prepared. It is dropped using a drop impact tester. Then, the number of occurrences of disconnection of the solder joint due to the drop impact is counted, and the distortion of the substrate is measured with a strain gauge. Quantitatively represents the reliability against dropping that can maintain the conduction of the solder joint.
Journal of Japan Institute of Electronics Packaging Vol. 6 No. 1 (2003) p. 73-79

  However, in the method described in Non-Patent Document 1, the following points are not considered. The strain gauge described in Non-Patent Document 1 does not directly measure the strain at the solder joint, and the mounting area of the strain gauge is larger than the area of the solder joint. For this reason, the measurement value by this strain gauge includes elements other than the stress acting on the solder joint, for example, the bending of the substrate, etc., and the solder joint obtained by the method described in Non-Patent Document 1 The numerical value that quantitatively represents the reliability with respect to the drop of the part does not accurately represent the reliability with respect to the drop of the solder joint.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a test substrate and a joint capable of accurately measuring stress due to a drop impact applied to a joint portion between the electronic component and the substrate. It is to provide a stress measurement method for a part.

  A first feature according to an embodiment of the present invention is that, in a test substrate, a substrate, a first electrode provided on a surface of the substrate, a piezoelectric element stacked on the first electrode, and the piezoelectric A second electrode stacked on the element; a first external terminal provided on the substrate and connected to the first electrode; and a second external terminal provided on the substrate and connected to the second electrode A terminal.

  According to a second aspect of the present invention, in the stress measurement method for a joint portion, the test substrate obtained by bonding an electronic component to the second electrode of the test substrate according to claim 1 is used as a drop impact tester. A step of dropping the test substrate in the drop impact tester to apply an impact to the piezoelectric element, a signal output from the piezoelectric element due to the impact is detected, and the second electrode and the electron Measuring the stress at the joint with the component.

  ADVANTAGE OF THE INVENTION According to this invention, the stress by the drop impact added to the junction part of an electronic component and a board | substrate can be measured with a sufficient precision.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
As shown in FIGS. 1 and 2, the test substrate 1 according to the first embodiment of the present invention has a plurality of mounting electrodes 3 and one stress on the surface of a substrate 2 formed of, for example, an epoxy resin. A measurement electrode 4 is formed. These mounting electrodes 3 and stress measurement electrodes 4 are arranged in an array. The stress measuring electrode 4 is positioned at one corner of the array in which the mounting electrode 3 and the stress measuring electrode 4 are arranged in an array. Further, the substrate 2 has a region different from the region where the mounting electrodes 3 are arranged, specifically, the first external terminal 5 and the second external terminal 6, and the first lead wiring in the peripheral portion of the substrate 2. 7 and the second lead-out wiring 8 are formed. The first lead wire 7 electrically connects the stress measurement electrode 4 and the first external terminal 5, and the second lead wire 8 electrically connects the stress measurement electrode 4 and the second external terminal 6. Connected.

  In the first embodiment, the case where one stress measurement electrode 4 is formed has been described as an example, but two or more stress measurement electrodes 4 may be formed. When two or more stress measuring electrodes 4 are formed, the first external terminal 5, the second external terminal 6, the first lead wire 7, and the second lead wire 8 are formed for each stress measuring electrode 4. Further, when two or more stress measurement electrodes 4 are formed, the position where the stress measurement electrodes 4 are formed is located at a corner portion of the plurality of mounting electrodes 3 arranged in an array. The replacement position is preferred.

  As shown in FIG. 2, the stress measuring electrode 4 is laminated on the first electrode 9 provided on the surface of the substrate 2, the piezoelectric element 10 laminated on the first electrode 9, and the piezoelectric element 10. And the second electrode 11. The first electrode 9 and the first external terminal 5 are electrically connected by the first lead wire 7, and the second electrode 11 and the second external terminal 6 are electrically connected by the second lead wire 8.

  In particular, the stress measuring electrode 4 of the test substrate 1 is formed by the steps shown in FIGS. 3 (a) to 3 (h).

  In the step shown in FIG. 3A, the copper thin film 12 is formed on the surface of the epoxy resin substrate 2. The copper thin film 12 is formed by electroplating, vapor deposition, or the like.

  3B, by etching the copper thin film 12, the first electrode 9, the first lead wiring 7, the first external terminal 5, and the plurality of mounting electrodes 3 (the first external terminal 5, A mounting electrode 3 is not shown). The first electrode 9, the first lead wire 7, the first external terminal 5, and the mounting electrode 3 are formed by forming a resist film on the copper thin film 12 and exposing the resist film to a predetermined pattern. A portion of the resist film that did not exist is removed to form a mask, and the copper thin film 12 is removed by etching using this mask. The mask is finally removed. An insulating film 13 is buried in a region other than the first electrode 9 and the like, and the entire surface of the substrate 2 is flattened.

  In the step shown in FIG. 3C, a sheet-like piezo film 10a is attached to the entire surface of the insulating film 13 including the first electrode 9. The piezo film 10a is attached using a conductive adhesive.

  The piezo film 10a is not particularly limited, but is a PDT series (see http://www.t-sensor.co.jp/PIEZO/FDT/) or DT series (http://www.t-sensor.co.jp/), which is manufactured by US MSI (Measurement Specialties, Inc). http://www.t-sensor.co.jp/PIEZO/DT/) can be used. This type of series piezo film 10a has good processability and can be easily reduced to, for example, 0.03 mm as compared with a hard piezoelectric element (such as a piezoceramic).

  That is, by forming the piezoelectric element 10 using the piezo film 10a, the entire thickness of the test substrate 1 including the piezoelectric element 10 is substantially the same as the thickness of the substrate not including the piezoelectric element 10.

  In the step shown in FIG. 3D, a mask 14 for patterning is formed on the piezo film 10a. As described in the process shown in FIG. 3B, the mask 14 forms a resist film on the piezo film 10a, exposes the resist film to a predetermined pattern, and removes the resist film in the unexposed portion. It is formed by removing.

  In the step shown in FIG. 3E, the piezo film 10a is etched using the mask 14, the piezo film 10a other than under the mask 14 is removed, and the piezo film 10a remaining under the mask 14 is used. The piezoelectric element 10 is formed. The mask 14 is removed thereafter.

  In the step shown in FIG. 3F, the insulating film 15 is embedded in a region other than the piezoelectric element 10, and the entire surface of the substrate 2 is flattened.

  In the step shown in FIG. 3G, the second electrode 11 is laminated on the piezoelectric element 10, and the second lead wire 8 and the second external terminal 6 (the second external terminal 6 are not shown) in the same layer. ) And are formed. The second electrode 11, the second lead wire 8, and the second external terminal 6 are formed by forming a copper thin film on the piezoelectric element 10 and the insulating film 15, and this copper thin film is formed in the step shown in FIG. As described, it can be formed by using a photolithographic technique and an etching technique. An insulating film 16 is embedded in a region other than the second electrode 11 and the like, and the entire surface of the substrate 2 is planarized.

  In the step shown in FIG. 3H, a solder resist 17 is applied on the second electrode 11, the second lead wiring 8, the second external terminal 6, and the insulating film 16. The solder resist 17 is applied so as to expose the surface of the second electrode 11 and cover the peripheral edge of the second electrode 11.

  By applying the solder resist 17 so as to cover the peripheral edge portion of the second electrode 11, the solder resist 17 exerts an action of pressing the stress measuring electrode 4. For this reason, during the drop impact test described later using the evaluation sample 19 (see FIG. 4) in which the electronic component 18 is soldered to the second electrode 11 of the test substrate 1, the gap between the second electrode 11 and the piezoelectric element 10 is determined. It is possible to increase the difficulty of peeling, and the difficulty of peeling between the piezoelectric element 10 and the first electrode 9.

  As shown in FIG. 4, the electronic component 18 is soldered to the test substrate 1 having the stress measurement electrode 4 using a solder (bump electrode) 20, thereby forming an evaluation sample 19. In FIG. 4, only a portion where one connection terminal (not shown) provided in the electronic component 18 is soldered to the second electrode 11 is shown. Although not shown, the plurality of mounting electrodes 3 on the test substrate 1 and the plurality of connection terminals of the electronic component 18 are also soldered using the solder 20.

  The evaluation sample 19 follows the actual product obtained by soldering electronic components to a substrate (product substrate) in which only the plurality of mounting electrodes 3 are arranged in an array without having the stress measurement electrode 4. Have been made. The difference between the evaluation sample 19 and the actual product is that the portion where the stress measurement electrode 4 is formed in the evaluation sample 19 is the mounting electrode 3 in the actual product. It is also possible to use the test substrate 1 as a product substrate as it is.

  By attaching the evaluation sample 19 to a drop impact tester 21 (see FIG. 5) and performing a drop impact test, stress acting on the solder joint between the second electrode 11 and the electronic component 18, particularly the solder joint, is applied. The applied vertical stress (stress generated in the direction perpendicular to the surface of the substrate 2) can be measured using the piezoelectric effect of the piezoelectric element 10. The piezoelectric effect is that a voltage corresponding to the amount of distortion is generated from the piezoelectric element 10 by applying distortion (deformation) to the piezoelectric element 10.

  As shown in FIG. 5, the drop impact testing machine 21 is held by a base 22, a plurality of (for example, three or four) columns 23 erected on the base 22, and the columns 23 can be moved up and down. The jig 24 is provided. The jig 24 is provided so as to be movable up and down between a rising position indicated by a solid line and a collision position indicated by a virtual line.

  A mounting portion 25 for attaching the evaluation sample 19 is provided on the upper surface side of the jig 24. A collision convex portion 26 is formed on the lower surface side of the jig 24. A collision receiving portion 27 is formed on the base 22. When the jig 24 is dropped from the raised position indicated by the solid line, the collision convex portion 26 collides with the collision receiving portion 27 when the jig 24 falls to the collision position indicated by the phantom line. Accompanying this collision, stress acts on the piezoelectric element 10 of the evaluation sample 19 attached to the jig 24 and the solder joint between the second electrode 11 and the electronic component 18.

  Between the first external terminal 5 and the second external terminal 6 of the evaluation sample 19 attached to the jig 24 and the voltmeter 28, a lead wire 29 which is a signal lead-out wire is connected. The voltmeter 28 measures the voltage generated by the piezoelectric effect in the piezoelectric element 10 during the drop impact test as a signal output from the piezoelectric element 10 during the drop impact test.

  When the dimension of the stress measuring electrode 4 is small, the voltage value output from the piezoelectric element 10 is expected to be small. In this case, a highly sensitive measurement system is required. However, since the lead wire 29 is long, the sensitivity is deteriorated, and the output from the piezoelectric element 10 cannot be measured with high accuracy. In order to solve this problem, the amount of charge that is not affected by the partial influence of the lead wire 29 is measured, and the stress value acting on the solder joint is obtained. For the measurement at this time, a charge amplifier that converts the charge amount into a voltage signal is used.

  Here, the steps of the stress measurement method for measuring the stress acting on the solder joint between the second electrode 11 and the electronic component 18 in the evaluation sample 19 performed using the drop impact tester 21 are shown in FIG. This will be described with reference to a flowchart.

  First, the electronic component 18 is soldered to the test substrate 1 to produce an evaluation sample 19 (S1). The produced evaluation sample 19 is attached to the jig 24 of the drop impact tester 21 (S2). The jig 24 to which the evaluation sample 19 is attached is held in the raised position.

  Next, a lead wire 29 is connected between the first external terminal 5 and the second external terminal 6 formed on the evaluation sample 19 attached to the jig 24 of the drop impact tester 21 and the voltmeter 28 ( S3).

  After the connection of the lead wire 29 is completed, the jig 24 held at the raised position is dropped together with the evaluation sample 19 to the collision position, and a solder joint between the second electrode 11 and the electronic component 18, and An impact is applied to the piezoelectric element 10 (S4).

  When an impact is applied to the piezoelectric element 10, a voltage due to the piezoelectric effect is generated from the piezoelectric element 10, and the generated voltage is measured by the voltmeter 28 (S5).

  The stress value acting on the solder joint portion is converted from the voltage value measured by the voltmeter 28 to obtain the stress value acting on the solder joint portion between the piezoelectric element 10 and the second electrode 11 and the electronic component 18. (S6).

  Furthermore, the drop impact test is repeated while changing the drop height, and the stress value acting on the solder joint between the piezoelectric element 10 and the second electrode 11 and the electronic component 18 is obtained, and for each drop impact test. The conduction state of the solder joint between the second electrode 11 and the electronic component 18 is measured (S7). As a result, the correlation between the stress value acting on the solder joint between the second electrode 11 and the electronic component 18 and whether or not conduction can be maintained according to the stress value can be obtained. And the reliability with respect to the fall of a solder joint part is quantitatively expressed using the maximum stress value of the range which can maintain conduction (S8).

  Here, in the measurement of the stress acting on the solder joint between the second electrode 11 and the electronic component 18 performed using the evaluation sample 19, the piezoelectric element 10 formed in substantially the same area as the solder joint is used. Therefore, the actual stress acting on the solder joint can be measured with high accuracy. And since this evaluation sample 19 is manufactured by copying an actual product obtained by soldering an electronic component to an actual substrate, it is substantially the same as the stress acting on the solder joint when the actual product falls. Stress can be measured. For this reason, the measurement result obtained by the drop impact test can be effectively reflected in the reliability design for the actual product drop.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same component as the component demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted.

  The basic configuration of the second embodiment is the same as that of the first embodiment. The difference between the second embodiment and the first embodiment is that the value of the stress acting on the solder joint between the second electrode 11 and the electronic component 18 is measured during the drop impact test. In addition, it is a point to automatically measure the conduction state between the second electrode 11 and the electronic component 18.

  In the test substrate 1A of the second embodiment, a circuit 31 connected to the mounting electrode 30 formed on the test substrate 1A is formed compared to the configuration of the test substrate 1 described in the first embodiment. ing. When the evaluation sample 19A is formed by soldering the electronic component 18 to the test board 1A, the second electrode 11 and the electronic component 18 are connected by the circuit 31, the circuit 32 in the electronic component 18, and the second lead wiring 8. A continuity measuring circuit 33 for measuring the continuity between them is formed.

  In the stress measurement method for measuring the stress acting on the solder joint between the second electrode 11 and the electronic component 18 in the evaluation sample 19A of the second embodiment, the stress measurement method described in the first embodiment 6 is added to the power source 34 and the ammeter 35 functioning as a continuity detection unit using the continuity detection line 36 in series, and the measurement of the continuity state indicated by S7 in FIG. 6 is added. Instead of the process, measurement of the conduction state using the ammeter 35 is performed.

  The timing at which the continuity of the solder joint between the second electrode 11 and the electronic component 18 becomes defective during the drop impact test can be confirmed by the measurement result of the ammeter 35. Then, based on the measurement result of the ammeter 35 and the measurement result of the voltmeter 28, when the stress value acting on the solder joint between the second electrode 11 and the electronic component 18 is any, the solder joint It is possible to measure with high accuracy whether the continuity is poor.

  In the first and second embodiments described above, the bonding between the second electrode 11 and the electronic component 18 has been described by taking solder bonding as an example. The joining with the component 18 is not limited to the solder joining. For example, the present invention can be applied to the case of joining with a conductive adhesive of silver paste.

  In the first embodiment and the second embodiment described above, the mounting electrodes 3 and 30 and the stress measurement electrode 4 are described as an example. The shapes of the electrodes 3 and 30 and the stress measurement electrode 4 are not limited to a circle, and may be, for example, a rectangle.

1 is a plan view showing a test board according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the electrode for stress measurement in the test board | substrate shown in FIG. FIG. 3 is a process diagram showing a process of forming the stress measurement electrode shown in FIG. 2. It is sectional drawing which shows the part of the electrode for stress measurement in the evaluation sample which electronically soldered the electronic component to the test board | substrate. It is the schematic which shows a drop impact tester. It is a flowchart which shows the process of the stress measuring method which measures the stress which acts on a solder joint part. It is sectional drawing which shows the part of the electrode for stress measurement in the evaluation sample which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Test board, 1A ... Test board, 2 ... Board, 5 ... 1st external terminal, 6 ... 2nd external terminal, 9 ... 1st electrode, 10 ... Piezoelectric element, 10a ... Piezo film, 18 ... Electronic component, 21 ... Drop impact tester

Claims (4)

A substrate,
A first electrode provided on a surface of the substrate;
A piezoelectric element laminated on the first electrode;
A second electrode laminated on the piezoelectric element;
A first external terminal provided on the substrate and connected to the first electrode;
A second external terminal provided on the substrate and connected to the second electrode;
A test board comprising:   The test substrate according to claim 1, wherein the piezoelectric element is a piezo film. Attaching the test board obtained by bonding an electronic component to the second electrode of the test board according to claim 1 to a drop impact tester;
Dropping the test substrate in the drop impact tester and applying an impact to the piezoelectric element;
Detecting a signal output by the impact from the piezoelectric element, and measuring a stress at a joint portion between the second electrode and the electronic component;
A method for measuring stress in a joint, comprising: The joint stress according to claim 3, further comprising a step of supplying a signal to a joint portion between the second electrode of the test substrate and the electronic component and measuring a damage state of the joint portion. Measuring method.

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