CN108225963B

CN108225963B - PCB design method based on BGA solder joint reliability test

Info

Publication number: CN108225963B
Application number: CN201711489462.4A
Authority: CN
Inventors: 李加全; 周波; 林茂
Original assignee: Shenzhen Fastprint Circuit Tech Co Ltd; Guangzhou Fastprint Circuit Technology Co Ltd; Yixing Silicon Valley Electronic Technology Co Ltd
Current assignee: Shenzhen Fastprint Circuit Tech Co Ltd; Guangzhou Fastprint Circuit Technology Co Ltd; Yixing Silicon Valley Electronic Technology Co Ltd
Priority date: 2017-12-30
Filing date: 2017-12-30
Publication date: 2020-11-13
Anticipated expiration: 2037-12-30
Also published as: CN108225963A

Abstract

The invention discloses a PCB design method based on BGA solder joint reliability test, which comprises the following steps: welding the BGA module on a PCB to obtain a device to be tested, wherein a welding spot array of the device to be tested comprises a plurality of welding spot rings which are different in spacing from the center of the welding spot array; putting a device to be tested into a test box; selecting a welding spot ring to be tested to obtain test rings, and connecting at least two welding spots of each test ring with the resistance test system by adopting a connecting wire to form a test path; starting the test box, and starting the resistance test system to continuously measure the resistance of the test paths corresponding to different test rings; and obtaining the failure condition of the welding spot corresponding to each test ring according to the change of the measured resistance, and obtaining the design scheme of the PCB according to the failure condition of the welding spot of each test ring. The invention adopts a mode of measuring the welding spots on different welding spot rings by the resistance test system, accurately obtains the reliability of the BGA welding spots with different distances from the center, and provides reference for the BGA size design under specific use conditions.

Description

PCB design method based on BGA solder joint reliability test

Technical Field

The invention relates to the technical field of printed circuit boards, in particular to a PCB design method based on BGA welding spot reliability test.

Background

BGA (ball Grid array) packaging, i.e., ball Grid array packaging, is a method in which array solder balls are formed on the bottom of a substrate of a package body to serve as I/O terminals of a circuit and to be interconnected with a Printed Circuit Board (PCB), and BGA packaging technology has been widely used in the fields of integrated circuits and electronic packaging. With the increasing packaging density, new materials such as lead-free solder balls, high-lead solder balls and underfill are added, and new processes such as CBGA (Ceramic Ball Array) packaging, PBGA (Plastic Ball Array) packaging and BGA underfill (Under Fill) are applied, so that the BGA solder joint is prone to failure, and the BGA size has a certain influence on the service life of the solder joint. Therefore, under the premise of no change in material and process conditions, how to design the PCB to improve the packaging quality becomes an urgent problem to be solved in the design of electronic packaging.

Disclosure of Invention

Based on the method, the resistor test system is adopted to measure the welding points on different welding point rings, so that the reliability of the BGA welding points with different distances from the center is accurately obtained, and reference is provided for the size design of the BGA on the PCB.

In order to achieve the purpose, the invention adopts the following technical scheme:

a PCB design method based on BGA solder joint reliability test comprises the following steps:

welding the BGA module on a PCB to obtain a device to be tested, wherein a welding spot array is arranged in the device to be tested, and the welding spot array comprises a plurality of welding spot rings which are different in spacing from the center of the welding spot array;

putting the device to be tested into a test box, wherein the test box is used for providing a stress test environment for the device to be tested;

selecting a welding spot ring to be tested to obtain a test ring, and connecting at least two welding spots of each test ring with the resistance test system by adopting a connecting wire to form a test path;

starting the test box, and continuously measuring the resistance of the test paths corresponding to different test rings by the resistance test system;

and obtaining the failure condition of the welding spot corresponding to each test ring according to the change of the measured resistance, and obtaining the design scheme of the PCB according to the failure condition of the welding spot of each test ring.

In one embodiment, before the step of soldering the BGA module to the PCB, the method further comprises the steps of:

and manufacturing a PCB, wherein test points outside the BGA mounting area are manufactured on the PCB, the test points correspond to the tested welding points one by one and are conducted with the tested welding points, and the welding points are connected with the connecting lines through the test points.

In one embodiment, the test point is located on a solder surface of the PCB, the solder surface is further provided with a lead-out wire, and the test point is conducted with the via hole through the lead-out wire.

In one embodiment, the test point includes a test hole plated with a conductive metal, and the connection line is inserted into and soldered to the test hole.

In one embodiment, the pads tested on the test ring include four pads at four corners of the pad ring.

In one embodiment, one of the welding points is connected with a positive terminal of the resistance testing system, and the remaining three welding points are connected with a negative terminal of the resistance testing system; or three of the welding spots are connected with the positive terminal of the resistance testing system, and the rest welding spot is connected with the negative terminal of the resistance testing system.

In one embodiment, the test chamber comprises a temperature impact test chamber for providing alternating temperature impact stress to the device under test during the measurement and a vibration test chamber for providing mechanical stress to the device under test during the measurement, the device under test being located in the temperature impact test chamber or the vibration test chamber during the test.

In one embodiment, the step of obtaining the failure condition of the solder joint corresponding to each test ring according to the change of the measured resistance specifically includes: and judging whether the measured resistance is suddenly increased within preset test time, if so, indicating that the measured welding point fails under the stress test environment, otherwise, indicating that the measured welding point does not fail under the stress test environment.

The invention has the beneficial effects that:

according to the PCB design method based on BGA welding spot reliability test, the stress test environment is provided through the test box, then the device to be tested is placed in the test box and is connected with the resistance test system to realize resistance on-line test, so that the failure condition of welding spots on different welding spot rings under certain environmental stress is measured, and the reliability service life of the welding spots of different welding spot rings can be measured. When the fact that the welding spot on the welding spot ring which is more than a certain distance away from the center is easy to lose efficacy is found, reference can be provided for the size design of a BGA mounting area on a PCB, or the PCB material with different thermal expansion coefficients can be replaced according to actual needs, so that the failure condition of the welding spot is improved, and the packaging quality is improved.

Drawings

FIG. 1 is a flow chart of a PCB design method based on BGA solder joint reliability test according to an embodiment of the present invention;

FIG. 2 is a system diagram of a BGA solder joint reliability test according to an embodiment of the present invention;

FIG. 3(a) is a schematic view of the CS surface on the PCB of FIG. 2; FIG. 3(b) is a schematic view of the SS side on the PCB of FIG. 2;

FIG. 4(a) is a schematic diagram of resistance change when a solder joint does not fail in a BGA solder joint reliability test process according to an embodiment of the present invention; fig. 4(b) is a schematic diagram of resistance change under a solder joint failure condition in the BGA solder joint reliability test process according to an embodiment of the present invention.

Description of reference numerals:

100. the device to be tested comprises a device to be tested, 110, a packaging substrate, 111, solder balls, 120, PCBs, 121, via holes, 122, bonding pads, 123, leading-out wires, 124, test points, 200, connecting wires, 300, a resistance test system, 400 and a test box.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and the detailed description. It should be understood that the detailed description and specific examples, while indicating the scope of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

It will be understood that when an element is referred to as being "on" another element, it can be directly on the other element or be on the other element with an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. Also, as used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Referring to fig. 1, a PCB design method based on BGA solder joint reliability test in an embodiment of the present invention is characterized by comprising the following steps:

s110: the BGA module is soldered onto the PCB 120 to obtain the device under test 100 shown in fig. 2. The BGA module includes a package substrate 110 and a plurality of solder balls 111 disposed on one surface of the package substrate 110. Referring to fig. 3(a), the mounting area of the PCB 120 is provided with pads 122 corresponding to the solder balls 111 and vias 121 corresponding to the pads 122, and the pads 122 are electrically connected to the vias 121. One pad is formed between each solder ball 111 and the corresponding pad 122, and a plurality of the pads form an array of pads. The pad array includes a plurality of pad rings at different spacings from a center of the pad array.

S120: the device under test 100 is placed in a test chamber 400, and the test chamber 400 is used to provide a stress test environment for the device under test 100.

The reliability of a solder joint can be calculated and expressed by the time it takes to fail under a particular environmental stress from the time it begins to withstand the stress.

S130: determining the solder joint rings to be tested, obtaining test rings, and connecting at least two solder joints of each test ring with a resistance test system 300 by using a connecting wire 200 (resistance test wire) to form a test path.

The determination of the test ring may be performed by selecting a plurality of solder joint rings according to actual needs, as shown in fig. 3(B), the solder joint rings selected in the test are a test ring a, a test ring B, and a test ring C, and the dashed rectangle in the figure is only used to illustrate the solder joint rings, and cannot represent the solid structure on the PCB 120. Multiple test rings may be connected to the resistance testing system 300 together, and the resistance testing system 300 may automatically and continuously measure different test rings.

It should be noted that, in this step, the connection line 200 may be directly connected to the pad or indirectly connected to the pad, for example, connected to the pad through the test point 124.

S140: the test chamber 400 is opened, and the resistance testing system 300 starts to continuously measure the resistance of the test paths corresponding to different test rings.

After the resistance testing system 300 has measured one test path, it will automatically measure the next test path. For the same BGA, reliability data of BGA welding spots with different distances from the center can be obtained only by enabling welding spots on the welding spot ring with different distances from the center to form a test path with the on-line test system.

S150: and obtaining the failure condition of the welding point corresponding to each test ring according to the change of the measured resistance, and obtaining the design scheme of the PCB 120 according to the failure condition of the welding point of each test ring.

According to the physical principle, when the cross-sectional area of the conductor changes, the resistance value of the conductor also changes: when the same current passes through the conductors with the same material and different thicknesses, the thicker conductor has smaller resistance due to the large cross-sectional area; thinner conductors have higher resistance due to their smaller cross-sectional area. The basic principle of the welding spot reliability testing method is that welding spot failure is accompanied with welding spot cracks and welding spot cracking phenomena, the cross section area of the connected part is reduced, and the resistance is increased. Therefore, it can be determined whether the measured resistance suddenly increases under the environmental stress and within the preset test time, and if the measured resistance value does not change or changes little, it indicates that the measured solder joint does not fail under the stress test environment, as shown in fig. 4 (a); if the measured resistance value suddenly increases, the measured welding point fails under the stress test environment, as shown in FIG. 4 (b). It should be noted that, the testing time may not be set, and the on-line testing is continued until the solder joint fails, so that the life length of the solder joint can be obtained.

During testing, it was found that solder joint failure was related to the distance from the center of the solder joint array, with longer distances leading to greater accumulated strain and greater susceptibility to failure. Therefore, when it is found that the solder joint on the solder joint ring beyond a certain distance is prone to failure, a reference can be provided for the BGA pad size design on the PCB 120, so as to design the corresponding pad 122, via 121 and trace. Or under the condition that the welding point of the target BGA size is easy to fail, the original BGA size can be kept, the failure condition of the welding point can be improved by replacing the PCB 120 material with different thermal expansion coefficients or changing the size of the welding pad 122 according to actual needs, and the packaging quality is improved.

For example, as shown in fig. 3(B), when it is found that the solder joint failure occurs in the test ring C and the failure of the test rings a and B has not occurred temporarily within the specified test time, the BGA mounting area on the PCB 120 can be sized to fit the test ring B. Or, in the case that the customer requires that the BGA size cannot be changed, the material of the PCB 120 substrate is changed to reduce the difference between the thermal expansion coefficients of the PCB and the BGA module, thereby improving the solder joint failure.

It should be noted that the present invention is not necessarily executed in strict sequence of S110-S120-S130-S140-S150, and may also be executed in sequence of S110-S130-S120-S140-S150.

Further, in the present embodiment, before step S110, step S100 is further included:

and manufacturing the PCB 120, referring to fig. 3(b), manufacturing test points 124 outside the BGA mounting region on the PCB 120, where the test points 124 are in one-to-one correspondence with the tested solder joints and are conducted. The solder joint is connected to the connection line 200 through the test point 124. Through being provided with the test point 124 that is located outside BGA pastes dress district on PCB 120, the line is connected when convenient the test, and connecting wire 200 need be connected with intensive solder joint or via hole 121 when preventing the test, increases the connection degree of difficulty, also influences the measuring accuracy.

Further, the test point 124 is located on an SS (solder side) surface of the PCB 120, the SS surface is further provided with a lead-out wire 123, and the test point 124 is conducted with the via hole 121 through the lead-out wire 123. The test point 124 is conducted with the solder joint through the lead-out wire 123 and the via hole 121. The test point 124 is arranged on the SS surface of the PCB 120, which is beneficial to realizing the conduction between the test point 124 and the solder joint, because the available space between the through holes 121 on the SS surface is larger, the lead-out wire 123 is conveniently etched in the space, and the connection between the test point 124 and the through holes 121 is realized through the lead-out wire 123. While the vias 121 on the CS (Component Side) plane are affected by the pads 122, the pinouts 123 are difficult to arrange, but it is understood that in other embodiments, the test points 124 may be arranged on the CS plane. The current trend during the test is described below: the current starts from the positive electrode of the resistance testing system 300, and reaches one solder joint after passing through one connecting line 200, one test point 124, the corresponding outgoing line 123 and the corresponding via hole 121, the solder joint is conducted with another solder joint, the dotted line in fig. 2 represents a wiring schematic between two solder joints in the package substrate 110, and the current continues to reach the negative electrode of the resistance testing system 300 after passing through another solder joint, the corresponding via hole 121, the corresponding outgoing line 123, the corresponding other test point 124 and the other connecting line 200.

In this embodiment, the test points 124 include test holes that are plated with a conductive metal. In step S130, the connection line 200 is inserted into the test hole and welded during the test process, so as to ensure the connection during the test and ensure the test accuracy.

Furthermore, optionally, the solder points tested on the test ring are mainly four solder points on four corners of the solder point ring, as shown in fig. 3(b), and accordingly, the connecting lines 200 are connected to the corresponding test points 124, so that the reliability of the solder points on the solder point ring can be determined more accurately. Because the inventors have demonstrated through extensive experimentation that the solder joints at the four corners of a solder joint ring are most susceptible to failure, the larger the size of the BGA, the shorter the reliability life of the solder joints at the four corners. The reason for this is mainly because the welding points at the four corners have the longest distance from the center, and the accumulated strain is the largest, so that cracking is more likely to occur. Therefore, the invention innovatively measures the welding spots on the four corners of the test ring, can better reflect the failure condition of the welding spot ring, and can obtain effective results through fewer tests. It should be noted that, during the testing process, other solder points on the test ring may also be measured, and those skilled in the art may select the solder points to be tested according to actual needs.

Specifically, referring to fig. 3(b), in the four welding spots, one welding spot is connected to the positive terminal of the resistance testing system 300, and the remaining three welding spots are connected to the negative terminal of the resistance testing system 300 to form three testing paths, that is, each testing ring has three sets of testing results, and the reliability of the four welding spots can be obtained by comparing the three sets of testing results. For example, when the resistance value of each of the three groups of test results is suddenly increased, the welding point connected with the positive terminal post is possibly failed; or when the resistance value of a certain test path suddenly increases, it indicates that the solder joint connected with the negative terminal of the resistance test system 300 on the test path may fail. In other embodiments, the connection manner of the solder joints on the four corners may be as follows, wherein three solder joints are connected to the positive terminal of the resistance testing system 300, and the remaining solder joint is connected to the negative terminal of the resistance testing system 300, or three testing paths may be formed.

Optionally, the test chamber 400 includes a temperature shock test chamber 400 and a vibration test chamber 400. The temperature impact test box 400 is used for providing alternate temperature impact stress for the device to be tested 100 in the measurement process, and the object generates stress due to expansion with heat and contraction with cold under different temperature conditions; the vibration test chamber 400 is used to provide mechanical stress to the device under test 100 during measurement. During testing, the device under test 100 is placed in one of the temperature shock test chamber 400 or the vibration test chamber 400.

In summary, the PCB design method based on the BGA solder joint reliability test of the present invention can conveniently and quickly determine the reliability life of solder joints on the BGA with different distances from the center, and after determining the life of these solder joints, can provide a reference for the dimensional design of the BGA under specific use conditions. The PCB design method has the following characteristics: 1. the principle is simple, and the operation is easy; 2. the required equipment is simple, only the necessary reliability test box 400, the resistance test connecting wire 200 and the on-line resistance test system 300 are needed, and the test cost is low; 3. reliability life data of welding spots on the BGA, which are different in distance from the center and have high test and analysis efficiency can be obtained in continuous test.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims

1. A PCB design method based on BGA solder joint reliability test is characterized by comprising the following steps:

selecting a welding spot ring to be tested to obtain a test ring, and connecting at least two welding spots of each test ring with the resistance test system by adopting a connecting wire to form a test path; when the failure condition of one welding spot ring is found in the specified test time and the failure condition of the other test rings is not found, the BGA mounting size on the PCB can be designed to be the size suitable for the test rings which are not failed;

the failure of the welding spot is related to the distance from the center of the welding spot array, when the welding spot on the welding spot ring exceeding a certain distance is found to be easy to fail, a welding spot, a through hole and a routing in a BGA mounting area are designed according to the failure distance, or the original BGA mounting size is reserved, and the failure condition of the welding spot is improved by replacing PCB materials with different thermal expansion coefficients or changing the size of the welding spot according to actual needs;

starting the test box, and continuously measuring the resistance of the test paths corresponding to different test rings by the resistance test system; the test box comprises a temperature impact test box and a vibration test box, wherein the temperature impact test box is used for providing alternating temperature impact stress for the device to be tested in the measuring process, and the vibration test box is used for providing mechanical stress for the device to be tested in the measuring process;

2. The method of claim 1, further comprising the step of, before the step of soldering the BGA module to the PCB:

3. The PCB design method based on the BGA solder joint reliability test of claim 2, wherein the test points are located on a solder surface of the PCB, the solder surface is further provided with lead-out lines, and the test points are conducted with the via holes through the lead-out lines.

4. The method of claim 2 or 3, wherein the test points comprise test holes plated with conductive metal, and the connection wires are inserted into and soldered to the test holes.

5. The method of claim 1, wherein the pads tested on the test ring include four pads at four corners of the pad ring.

6. The PCB design method based on BGA solder joint reliability test of claim 5, wherein one of the solder joints is connected with a positive terminal of the resistance test system, and the remaining three solder joints are connected with a negative terminal of the resistance test system; or three of the welding spots are connected with the positive terminal of the resistance testing system, and the rest welding spot is connected with the negative terminal of the resistance testing system.

7. The method of claim 1, wherein the device under test is located in the temperature shock test chamber or vibration test chamber during the test.

8. The method for designing a PCB based on BGA solder joint reliability test of claim 1, wherein the step of obtaining the failure condition of the solder joint corresponding to each test ring according to the variation of the measured resistance includes: and judging whether the measured resistance is suddenly increased within preset test time, if so, indicating that the measured welding point fails under the stress test environment, otherwise, indicating that the measured welding point does not fail under the stress test environment.

9. The method for designing a PCB based on BGA solder joint reliability test of claim 1, wherein the step of starting the resistance test system to continuously measure the resistance of the test paths corresponding to different test rings according to the opening of the test chamber includes: after the resistance testing system measures one testing path, the next testing path is automatically measured.

10. The method of claim 9, wherein the step of the resistance testing system starting to continuously measure the resistance of the test paths corresponding to different test rings according to the opening of the test chamber comprises: for the same BGA, reliability data of BGA welding spots with different distances from the center can be obtained only by enabling welding spots on the welding spot ring with different distances from the center to form a test path with the on-line test system.