JP2003174239A - Fraction lifetime improving scope of solder junction by regulating thermal expansion amount difference between printed board and component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the fraction lifetime of a solder junction by reducing the thermal expansion amount difference generated between a printed board and an electronic component when an electric product generates heat. <P>SOLUTION: In order to set the thermal expansion amount difference between the component and the printed board 2 to the same degree with respect to the peripheral part in which a component having a short fracture lifetime of the solder junction is mounted, an instrument 1 for regulating the thermal expansion of the board 1 is mounted on the board. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a hole or groove around a component on a printed circuit board, and a device for controlling thermal expansion is installed in the hole or groove to provide a space between the printed circuit board and the component. The purpose is to reduce the occurrence of a difference in thermal expansion that occurs in 1) and improve the fracture life of the solder joint.

[0002]

2. Description of the Related Art Regarding solder joints of electronic components mounted on a printed circuit board, conventional techniques have taken measures to extend the fracture life of the solder joints by devising the form and solder shape of the lead portions of the components. Came.

However, in recent years, it has become gradually difficult to take the conventional measures due to the increase in package density and the increase in package size accompanying one-chip packaging and the diversification of bonding forms.

[0004]

Many electronic components have a coefficient of thermal expansion different from that of a printed circuit board, and in general, there are many components having a thermal expansion coefficient lower than that of the printed circuit board. For example, the thermal expansion coefficient of the printed circuit board is 15e.
It is around -6, but about 2.0e-6 for Si, about 6.0e-6 for ceramics, 20 for plastic mold.
It has a coefficient of thermal expansion of e-6. Therefore, when the product is used, heat is generated by the components and thermal expansion occurs between the components and the printed board, and shearing, pulling and compressing forces are applied to the solder joints.

It is a problem to be solved by the present invention that the life of the solder joint portion of the component is shortened due to these reasons.

[0006]

SUMMARY OF THE INVENTION In the present invention, the solder joint has a peripheral portion on which parts having a short breaking life are mounted,
In order to make the thermal expansion amounts of the component and the printed circuit board similar, a process for adjusting the thermal expansion of the printed circuit board is performed.

When the thermal expansion amount of the printed circuit board is larger than the thermal expansion amount of the component, as shown in FIG. 1, in the product substrate of No. 2, a hole is made around the component, and a high rigidity indicated by 1 is formed there. Insert the rod and fix it inside the product housing. Alternatively, as shown in FIG. 2, a groove or hole as shown by 4 is formed around the component, and a frame made of a high rigidity and low expansion material as shown by 3 is inserted so as to cover or surround the component in the groove or hole. .

Similarly, when the thermal expansion amount of the printed circuit board is smaller than the thermal expansion amount of the component, a hole is formed around the component as shown in FIG. Insert a frame made of expansive material. It is the gist of the present invention to obtain the effect of improving the fracture life of the solder joint by this means.

[0009]

DETAILED DESCRIPTION OF THE INVENTION

[First Embodiment] As shown in FIG. 3B, a 2.5 mm square FR4 printed board on which one 7 mm square flip chip (hereinafter FC) is mounted as shown in FIG. A heat cycle test was conducted. History condition is 20 ℃
→ 125 ° C. → −55 ° C. → 20 ° C., 1200 cycles, and temperature raising / cooling rate were both 30 (deg./min.). The number of substrate samples was 30.

For the FC solder joint on the substrate, see FIG.
As shown in No. 7, eight check pads were provided and the conduction state was constantly monitored. These eight locations correspond to the contacts represented by 9 in FIG. The FC was designed in such a way that at each corner, the current entered at one contact and exited at the other, and the two contacts were considered to be life when either of them broke. In this test, it was decided that the solder joint was broken at the time when the electrical connection was lost and the current value became extremely unstable. In this test, the FC is not underfilled as often as it normally is.

Next, as shown in FIGS. 4 (a) and 4 (b), a printed circuit board similar to the one used in the previous test was placed on both sides of the chip component at a position 3 mm from directly below the end portion of the FC, and the means of the preceding paragraph was used. Same as the previous test for 30 printed circuit boards constrained by deformation using the same method and 30 printed circuit boards constrained by deformation using the means of the previous section as shown in FIGS. 5 (a) and 5 (b) at the same place. A thermal cycle test was conducted under the conditions. 4A and 4B, it is assumed that it is fixed to the product housing with a small temperature change, so that it is a high-rigidity / low-expansion material. A flat plate for restraining deformation was fixed to two invar (high rigidity / low expansion material) plates. Even when the above method is used, Invar having high rigidity and low expansion is used as the material of the frame. The heat cycle test was performed under the above conditions.

Taking a probability paper plot for the test results,
Comparing the number of fracture cycles at a cumulative failure rate of 60%, 200 cycles without expansion and deformation constraint, 600 cycles with expansion deformation by means of
It was 700 cycles when expanded and deformed by the means.

Further, regarding the unconstrained substrate, 2
When the amount of thermal expansion immediately below the FC end portion was measured at 0 ° C. → 125 ° C., the average value was 8.0 μm. The amount of thermal expansion when restrained by the means for it is 4.2 μm,
The average value of the amount of thermal expansion when restrained by the means of 3.2μ
It became m. The thermal expansion amount of the FC component alone not mounted was also measured by applying the same heat load. The average value of the amount of thermal expansion in the temperature change of 20 ° C. → 125 ° C. was 1.5 μm. Therefore, it was found that the operation according to the present proposal has an effect of making the thermal expansion amount of the printed circuit board near the FC of the printed circuit board close to the thermal expansion amount of the FC.

From this result, when the thermal expansion amount of the printed circuit board is larger than the thermal expansion amount of the component, the thermal expansion amount of the printed circuit board is locally restricted by the above method, and the thermal expansion amount of the chip component or the like is restrained. It was proved that by performing the matching operation, it has an effect of improving the fracture life of the solder joint.

[0015]

[Second Embodiment] As shown in FIGS. 5 (a) and 5 (b), the distance from the center of a FR4 printed circuit board of 70 mm square is 16 m.
One m-square CSP is mounted, and a duralumin (Al-
A frame of 4.0Cu-0.5Mg-0.5Mn) was inserted and fixed. This assumes that the substrate is fixed at the fixed position. A thermal cycle test was performed on this sample. The history condition is 20 ° C. → 125 ° C. → −55 ° C. → 20 ° C. for 2000 cycles, and the heating / cooling rate is 30 (de
g. / Min. ). The number of substrate samples was 10.

As shown in FIG. 3, eight check pads were provided on the solder joint portion of the CSP to constantly monitor the conduction state. These eight locations correspond to the contacts represented by 9 in FIG. The CSP was designed so that at each corner, the current entered at one contact and exited at the other, and when either of the two broke, the two contacts were considered to be life. In this test, it was decided that the solder joint was broken at the time when the electrical connection was lost and the current value became extremely unstable.

Next, for a printed circuit board similar to the one used in the previous test, a process for forcibly expanding the board portion around the CSP at a position 5 mm in the longitudinal direction from the land at the end of the CSP by the method described in the preceding paragraph. 30 printed circuit boards with
A thermal cycle test was conducted under the same conditions as the previous test.

Taking a probability paper plot for the test results,
Comparing the number of fracture cycles at a cumulative failure rate of 60%, it was 800 cycles when the frame of duralumin was not used and 1200 cycles when the frame was expanded and deformed by inserting the frame of duralumin.

The amount of thermal expansion between both ends of the CSP at 20 ° C. → 125 ° C. was measured for the unconstrained printed circuit board, and the average value was 10 μm. On the other hand, the average value of the amount of thermal expansion when the frame of the high expansion metal was fitted and forcedly expanded was 18 μm. Also, 16
The average value of the amount of thermal expansion of a mm square CSP component is 22 μm
Met. Therefore, it was found that the operation according to the present proposal has an effect of bringing the thermal expansion amount of the printed circuit board near the CSP of the printed circuit board close to the thermal expansion amount of the CSP.

From this result, when the thermal expansion amount of the printed circuit board is smaller than the thermal expansion amount of the component, the thermal expansion amount of the printed circuit board is locally adjusted to the thermal expansion amount of the electronic component by using the above method. It was proved that the operation has the effect of improving the fracture life of the solder joint.

[0021]

Many electronic components have a coefficient of thermal expansion different from that of printed circuit boards. When a component emits heat and causes thermal expansion between the component and the printed circuit board, shearing, pulling, and compressing forces are applied to the solder joint due to the difference in thermal expansion between the components. Due to these factors, the rupture life of the solder joint of the component is shortened, but the difference in thermal expansion amount can be reduced by the method shown in the present invention, and the rupture life of the solder joint can be extended.

[Brief description of drawings]

[Fig. 1] Product board in which high-rigidity plate materials (bars) are fitted around the parts in order to reduce the thermal expansion of the printed circuit board in order to achieve the same amount of thermal expansion as the parts with less thermal expansion. Represents

[Fig. 2] A product in which a high-rigidity / low-expansion frame material is fitted around the components in order to reduce the thermal expansion of the printed circuit board in order to achieve the same amount of thermal expansion as the components with less thermal expansion. A product in which a high-rigidity / high-expansion frame material is fitted around the component in order to increase the expansion amount of the printed circuit board in order to achieve the same amount of thermal expansion as the substrate or the component with large thermal expansion. Represents a substrate.

FIG. 3 is a diagram showing a printed circuit board on which components are mounted without adjusting a thermal expansion amount.

FIG. 4A is a view showing a mechanism of incorporating a highly rigid rod or plate around a component into a substrate. (B) A substrate for a heat cycle test in a state of being deformed and restrained by a highly rigid rod or plate around the component.

FIG. 5A is a diagram showing a mechanism of incorporating a highly rigid frame material around a component into a substrate. (B) Substrate for heat cycle test in a state where deformation is restricted by a frame material having high rigidity and low expansion around the component, or a portion around the component is expanded by the frame material having high rigidity and high expansion Represents

FIG. 6 is a diagram showing component-side contacts to be monitored.

[Explanation of symbols]

1 shows a highly rigid plate material for suppressing the amount of thermal expansion of the printed circuit board in the portion around the component. 2 Shows the board of the product. 3 High-rigidity / low-expansion frame material that aims to reduce the thermal expansion of the printed circuit board to achieve the same level of thermal expansion as parts with low thermal expansion, or parts with high thermal expansion The frame material has high rigidity and high expansion for the purpose of increasing the expansion amount of the printed circuit board in order to increase the thermal expansion amount. 4 Indicates holes or grooves for installing frame materials, plate materials, bar materials, etc. 5 Indicates FC parts or CSP parts. 6 shows a substrate for a heat cycle test. 7 shows a check pad for constant continuity monitoring during a heat cycle test. 8 High rigidity to fix high rigidity plate material (bar material) to suppress the amount of thermal expansion around the parts of the printed circuit board
A low expansion plate material is shown. 9 Shows a solder ball for continuity check

Claims (4)

[Claims] 1. A printed circuit board having a hole or groove for inserting a device for adjusting thermal expansion around an electronic component mounting portion on the printed circuit board. 2. A form of suppressing thermal expansion in which the housing and the printed circuit board are fixed to the printed circuit board according to claim 1 by a support rod or a support plate passing through holes around components. 3. The printed circuit board according to claim 1, wherein the holes around the electronic component are used as fixing portions to cover the upper side of the component.
Alternatively, by mounting a frame-shaped component made of a high-rigidity / low-expansion material so as to surround the lateral side, thermal expansion of the printed circuit board around the electronic component is suppressed. 4. The printed circuit board according to claim 1, wherein the holes around the electronic component are used as fixing portions to cover the upper side of the component.
Alternatively, by mounting a frame-shaped component made of a high-rigidity / high-expansion material so as to surround the lateral side, thermal expansion of the printed circuit board around the electronic component is promoted.