JPH11230878A - Method and device for testing resistance of substrate to bending of surface-mount component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heighten measurement accuracy in testing the resistance of a substrate to bonding by reducing the effects of variations in the hardness and thickness of substrates. SOLUTION: The amount of bending (amount of deflection) xi of a substrate 6 to be pressurized and bent by an indentor 2a and a pressurizing force fi are each measured by a displacement amount measuring device 3 and a pressuring force measuring device 4 to obtain the hardness of the substrate 6 ai =fi /xi . In addition, the hardness (a) (=(a pressurizing force)/(the amount of bending)) of a reference substrate is obtained in advance, and the normal amount of bending is corrected by the same ratio as a ratio between (a) and ai . The amount of bending after correction is obtained by xci =fi /a. Instead of correcting the normal amount of bending, a pressurizing force may be obtained by the expression fi =axi (xi is the normal amount of bending of the reference substrate) and be specified as fi .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for testing the bending resistance of a surface-mounted electronic component on a substrate and an apparatus used for the test.

[0002]

2. Description of the Related Art A strength test of a surface mount component (hereinafter, referred to as SMD) is performed by a method specified in JIS. JISC5
202 In the test method for board bending resistance specified in 6.1.4 (1), an SMD is mounted on a printed wiring board of a specified size and thickness, and this is used as a sample and supplied to a support table of a specified size. Place the test SMD so that it faces downward, press the board from the opposite side of the mounting surface with an indenter of a specified size from above and bend it until it reaches a specified bending amount (deflection amount). Investigate the presence / absence, deterioration of electrical characteristics, etc. With this method, the strength distribution of the SMD with respect to the bending amount can be known.

[0003]

In the test defined by JIS, the amount of applied stress is defined by the amount of bending of the substrate, and the measurement results are affected by variations in the hardness (Young's modulus) and thickness of the substrate. Vary widely.

[0004] The stress σ applied to the SMD at the time of substrate bending is S
Although it depends on each part of the MD, it is almost proportional to the amount of bending of the substrate and the hardness (Young's modulus) of the substrate.
Is actually proportional to the stress.

However, a general standard (JISC6484)
Does not specify the mechanical hardness, Young's modulus, and the like of the printed wiring board. Although the breaking strength called bending strength is specified, the specification such as Young's modulus has not been raised in the test method (JISC6481).

[0006] The thickness of the substrate used for the test is specified. However, in a generally used glass epoxy substrate, the Young's modulus differs even with a substrate having the same thickness depending on the material manufacturer of the epoxy resin, the temperature at the time of measurement, the amount of glass cloth, and the like.

[0007] Therefore, due to the variation of the Young's modulus and the variation of the substrate thickness within an allowable error, the stress applied to the SMD varies in the test method specified in JIS, and the measurement accuracy deteriorates.

Accordingly, an object of the present invention is to improve the measurement accuracy of a substrate bending resistance test by reducing the influence of variations in hardness, thickness, and the like of a substrate.

[0009]

In order to solve the above-mentioned problems, in the present invention, not only the amount of bending of the substrate but also the pressing force of the indenter are measured at the time of pressing by the indenter, and the rigidity of the substrate is measured. The applied stress is adjusted accordingly.

The adjustment of the applied stress can be performed by a method of correcting the prescribed bending amount of the substrate or a method of regulating the pressing force by the indenter.

In the case of the former method, the measured values of the pressing force by the indenter and the amount of substrate bending are respectively represented by f _i and x _i (where i is a subscript indicating the i-th data when there are a plurality of measured values). , The corrected substrate bending amount x _ci is given by x _ci = f
_The specified bending amount is corrected to x _ci by _obtaining the formula of _i / a (a is a constant obtained by f / x where x is the bending amount of the substrate as a reference of hardness and f is the pressing force).

[0012] In the latter method, a prescribed pressure f _i by the indenter, the f _i = ax _i (a bending amount of substrate as a hardness of the reference x, with f / x the pressure as f The obtained constant, x _i, is obtained by the formula of the prescribed bending amount of the reference substrate), and when the measured value of the pressing force becomes f _i , no more pressing force is applied to the substrate.

Incidentally, in order to conduct a test by such a method,
The test apparatus used in the present invention is provided with a pressing force measuring means in addition to the bending amount measuring means.

[0014]

According to the present invention, the hardness of the substrate is checked to reduce the fluctuation range of the applied stress, and the applied stress is adjusted according to the hardness. When the bending amount and the pressing force of the substrate are measured, the hardness of the substrate can be determined from the relationship between the two. In this way, the hardness of the substrate is determined,
When the applied stress is adjusted according to the hardness, the variation in the applied stress due to the variation in the hardness of the substrate can be absorbed, and the measurement accuracy is improved.

Incidentally, in order to adjust the applied stress, SM
Although it is necessary to know the stress actually applied to D, it is difficult to measure or calculate the stress actually applied. For this reason, first, the hardness of the reference substrate is determined.

The bending amount x and the pressing force f of the reference substrate are approximated to f = ax (a is a constant) from the least squares method from the measured data or the slope of a straight line drawn along a point plotted on the graph. Therefore, the hardness of the reference substrate is a =
f / x. On the other hand, it subjected試基plate actually applied pressure and bending amount of the measured value respectively f _i, when the x _i, hardness of the test試基 _{plate, a i = f i / x} i. The ratio _ai / a of the hardness of the reference substrate and the test substrate indicates the variation of the hardness of the test substrate as compared with the reference substrate. Therefore, the prescribed bending amount of the test board is corrected at the same ratio as the ratio (claim 2).
In this way, even if the actual applied stress is unknown, the applied stress on the test substrate can be made closer to the target value (the stress when the reference substrate is bent by a specified amount) to reduce the influence of the variation in the hardness of the substrate. it can.

The corrected substrate bending amount x _ci is x _ci / x _i =
From (f _i / x _i ) / a, it is obtained by the following equation. _{x ci = x i × (f} i / x i) / a = f i / a.

Since the relationship between the corrected substrate bending amount and the pressing force becomes f _i = ax _ci from x _ci = f _i / a, the pressing force f _i is specified instead of correcting the specified bending amount. The same result can be obtained by the method (claim 3). in this way,
The provisions bending amount of the reference substrate at the x _i, calculate the f _i in the formula f _i = ax _i, is used as defined pressure in the bending test it.

Rather than looking at the intensity distribution, in a test to confirm whether the SMD has a certain intensity, x _i
Of but it requires a reference value, the耐基plate bending test, who applied stress defined by the pressurizing force is convenient to be immediately available unnecessary measure f _i calculation.

[0020]

1 and 2 show an embodiment of a test apparatus according to the present invention.

In both figures, reference numeral 1 denotes a sample support of a prescribed size;
Reference numeral 2 denotes a pressurizing unit having an indenter 2a of a prescribed size, 3 denotes a displacement measuring device such as a dial gauge, 4 denotes a pressing force measuring device using a load cell or the like, and 5 denotes a sample on which a test SMD 7 is mounted on a printed circuit board 6. is there.

The pressing means 2 in FIG. 1 pushes down the indenter 2a by a mechanical pressing mechanism 2b. The mechanical pressurizing mechanism 2b may be of a type that pushes down the indenter 2a by a liquid pressure operated actuator regardless of whether it is a manual type or a power type. The pressurizing means 2 in FIG. 2 changes the rotation of the motor 2c into a linear motion by the motion conversion mechanism 2d and pushes down the indenter 2a.

The bending resistance test using these test devices is performed by placing the sample 5 on the support table 1 so that the SMD 7 faces downward as shown in the figure. In this state, the surface of the substrate 6 opposite to the mounting surface is pressed from above by the indenter 2a,
Deflect. Then, the bending amount and the pressing force at this time are measured by the displacement measuring device 3 and the pressing force measuring device 4.

Before that, the bending amount x of the reference substrate and the pressing force f
Is checked, and a reference value a = f / x of hardness is obtained in advance.

The hardness a _i = f of the substrate 6 is obtained from the measured values x _i and f _{i of the} amount of substrate bending and the pressing force by the measuring devices 3 and 4.
seeking _i / x _i, ends the bending of the substrate 6 where the measured value of the amount bending by correcting the x _i in the same ratio the ratio of a _i / a becomes the correction value _{x ci (= f i / a} ) I do.

[0026] Alternatively, termination from f _i = ax _i, the reference substrate specified amount to previously obtain a (x _i) Bending f _i when the, bending of the substrate 6 where the measured value of the pressure has reached the f _i I do.

FIG. 3 shows variations in the hardness (Young's modulus) of the substrate. In this figure, each substrate, now,
Assuming that is bent by 3 mm, the pressing force is about 11 kgf for the substrate, about 9 kgf for the substrate, and about 8 kgf for the substrate.
It becomes weak, and a large variation occurs in the applied stress.

On the other hand, when the amount of bending is corrected by the above-described method, when the substrate is set as a reference substrate, the specified bending amount of 3 mm is approximately 2.5 mm for the substrate, and the specified bending amount is approximately 2.5 mm for the substrate. 3mm is about 3.5mm
The pressure applied to each substrate is about 9k
gf. The same result is obtained when the pressure is initially set to about 9 kgf and pressurized.

As described above, since the stress applied to the SMD is almost proportional to the amount of bending and the hardness of the substrate, the less the amount of bending the harder the substrate, the smaller the variation in applied stress and the more stable the test conditions. Measurement accuracy is improved.

[0030]

As described above, in the test method of the present invention, since the applied stress is adjusted according to the hardness of the substrate, the influence of variations in the hardness of the substrate is reduced, and the measurement accuracy is improved.

In the method of adjusting the applied stress by correcting the amount of bending of the substrate, it is not necessary to detect the actual stress.
The complication of the test method and the test apparatus can be avoided. The same effect can be obtained by the method of defining the pressing force. In addition, this method does not need to calculate the correction value of the specified bending amount each time, and the test can be easily performed.

In addition to the above, the test apparatus of the present invention is provided with means for measuring the pressing force in addition to the means for measuring the amount of bending, so that the test can be performed by the above-described method.

[Brief description of the drawings]

FIG. 1 is a front view showing an embodiment of a test apparatus according to the present invention.

FIG. 2 is a front view of another embodiment.

FIG. 3 is a table showing variations in substrate hardness (Young's modulus).

[Description of Signs] 1 Sample support 2 Pressurizing means 2a Indenter 3 Displacement measuring device 4 Force measuring device 5 Sample 6 Substrate 7 SMD

Claims (4)

[Claims] 1. A surface-mounted component is mounted on a board of a specified size and thickness, and the sample is used as a sample and placed on a support of a specified size so that the surface-mounted component faces downward. The board is pressed from the opposite side of the mounting surface and bent until it reaches the specified bending amount.After that, in the board bending resistance test of the surface mounted component to check for the appearance abnormality of the surface mounted component and the deterioration state of the electrical performance, A board bending resistance test method for a surface-mounted component, comprising: measuring a bending amount and a pressing force of a board when pressurized by an indenter; and adjusting an applied stress according to the hardness of the board. 2. The method according to claim 1, wherein the adjustment of the applied stress is performed by correcting a prescribed bending amount of the substrate, and the correction is performed by measuring the measured values of the pressing force by the indenter and the bending amount of the substrate, respectively, f _i , x _i (where i is a plurality). , A subscript indicating that the data is the i-th data), the corrected substrate bending amount x _ci is given by x _ci = f
_2. The surface-mounted component according to claim 1, wherein _i / a (a is a constant obtained by f / x where x is a bending amount of the substrate as a reference of hardness and f is a pressure is f). Substrate bending resistance test method. The adjustment of the applied stress is performed by adjusting the pressing force f by an indenter.
_i , and the specified pressure f _i is given by f _i = ax
_The constant is determined by f / x where _i is a bending amount of the substrate as a reference of hardness and x is a pressing force and f / x is a pressing force, and x _i is a prescribed bending amount of the reference substrate. 2. The method for testing the bending resistance of a surface-mounted component according to 1 above. 4. A sample support having a prescribed size, a pressing means for pressing a substrate of a sample placed on the support from above with an indenter having a prescribed size to apply a bending force to the substrate, and a bending amount of the substrate. An apparatus for testing the bending resistance of a surface-mounted component on a substrate, comprising: means for measuring; and means for measuring a pressing force by an indenter, and capable of performing a test by the method according to claim 1.