JPH08124985A - Soldering inspection method of ball grid array - Google Patents

Abstract

PURPOSE: To provide a non-destructive inspection method which is capable of easily inspecting whether the terminals of a BGA(ball grid array) soldered to a printed board are regularly soldered to pads provided on the board or not. CONSTITUTION: A specific value h0 is previously obtained noticing a phenomenon that a gap between the undersides of the bodies of a BGA and the upside of a board is as large in size as the specific value h0 when solder is applied rightly on pads provided onto a board, and a non-destructive inspection is carried out to see whether the gaps h1 to h4 or h5 to h8 of a work soldered to the board are close enough to the specific value h0 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a board pad and a BG in mounting a BGA (ball grid array) on a board.
The present invention relates to a method for inspecting whether or not the terminals A are properly soldered.

[0002]

2. Description of the Related Art FIG. 3 is a perspective view of a BGA viewed from the terminal side. BGA is a type of imposition IC, and has a large number of terminals arranged in a grid pattern on the back surface of the body 1. This terminal is generally covered with a hemispherical solder 11. on the other hand,
FIG. 4 shows a board 2 on which the BGA is mounted, and pads 12 are formed at positions corresponding to the terminals of the BGA.
A method of soldering both will be described. First, a flux (activator) is applied on the pads 12 of the substrate 2 in advance. Next, attach the hemispherical solder 11 of the BGA terminal to this pad 1
The BGA body 1 is mounted on the substrate 2 in alignment with the position 2. Then, these are heated by an atmosphere furnace to melt the solder 11, and the both are soldered.

In this case, the soldered portion is BGA
Since it is hidden between the body 1 and the substrate 2, it was impossible to visually confirm the quality of soldering. Therefore,
Solder the test sample, peel off the soldered part, and if the solder is well attached, solder the product (work) used for the original purpose such as the product under the same conditions,
There have been performed methods such as a method of assuming that these works are properly soldered, and a method of inspecting by seeing through a soldering portion with X-rays.

However, it is difficult for the former to make all the soldering conditions the same. For example, even if the temperature is controlled, the temperature may slightly fluctuate up and down, the temperature stays in the furnace, and the solder is mounted on the board. The method of soldering differs depending on the heat capacity of the parts, and it is quite dangerous to say the quality of soldering only by the conditions of the test sample. The latter is X
Not only a high-priced inspection device called a line inspection device is required, but also when X-rays are irradiated from any direction, the images of the BGA terminals and the pattern of the board 2 overlap each other, and the quality of the soldered portion is good or bad. It was difficult and difficult to judge. As described above, in any of the conventional methods, the terminals on the back surface of the body 1 of the BGA and the pads 12 of the substrate 2 are solder 1
It was extremely difficult to nondestructively inspect that the soldering was correctly performed in No. 1.

[0005]

In the above-mentioned conventional technique, the test sample cannot represent all the soldering results due to the different conditions. Further, in X-ray fluoroscopy, it is difficult to obtain a critical image of the connection portion between the solder 11 and the pad 12 due to image overlap and the like, which requires skill and is difficult to judge the quality of the soldered portion. There was a physical defect. The present invention catches another characteristic phenomenon when the solder 11 is correctly attached to the pad 12 of the substrate 2, and judges the quality of the soldering by this, and the purpose is to detect the solder on the back surface of the BGA body 1. It is to provide a method of simply and correctly performing nondestructive inspection that the solder 11 of the terminal is soldered to the pad 12 on the substrate 2.

[0006]

In order to achieve the above-mentioned object, the present invention is characterized when the solder 11 is correctly attached to the pad 12 of the substrate 2, and the solder 11 of the BGA terminal is melted. At the same time, attention is paid to the phenomenon that the BGA body 1 sinks by a certain amount on the pads of the substrate 2 by spreading. That is, the size of the gap between the lower surface of the body 1 of the BGA and the upper surface of the substrate 2 is measured, and whether or not this is a characteristic value that occurs when soldering is correctly performed It is an inspection.

[0007]

The function of the present invention will be described. 5 and 6 are views showing a part of the BGA body 1 mounted on the substrate 2 as seen from a direction parallel to the surface of the substrate 2. 5 shows before soldering, and FIG. 6 shows after soldering. In FIG. 5, the size of the gap between the lower surface of the body 1 of the BGA and the upper surface of the substrate 2 is H. Next, when this is placed in a furnace and heated as described above, the solder 11 melts and spreads on the pads 12 of the substrate 2 in a wet state. At this time, since the outer shape of the solder is changed from the initial hemispherical shape to a drum shape, the BGA body 1 sinks and becomes as shown in FIG. 6, but the H value is naturally small and becomes h.

If h is a large value, the contact area between the solder 11 and the pad 12 is small, and the solder is not sufficiently attached. If the h is a small value, the solder is spread and the solder 11 is formed between the adjacent pads 12. Since they come into contact with each other, the h value h ₀ (optimum value) when the solder is properly attached is in the middle of this range. Although it depends on the amount of the solder 11 and the size of the pad 12, etc., if these amounts are fixed in advance, h ₀ can be easily obtained by an experiment. Therefore, it is possible to perform the soldering inspection by measuring the h value of the BGA after the soldering and determining whether or not the h value falls within the h ₀ category.

Since it is assumed that the bottom surface of the body 1 of the BGA is soldered without being parallel to the surface of the substrate 2 as shown in FIG. 7, for example, in the first method of the present invention, h It is necessary to measure at least four corners or four sides of the body 1 of the BGA to confirm that each h value is within the range of h ₀ , but since the measurement can be performed easily,
It does not hinder efficiency at all.

[0010]

1 is a perspective view showing a BGA mounted and soldered on a substrate 2 according to the first method of the present invention.
Is BGA body, 2 is substrate, 11 is solder, 12 is B
These are pads on the substrate 2 provided at positions corresponding to the terminals of the GA. Next, the soldering inspection method is as shown in FIG.
The dimensions of the gaps (h _{1 to} h ₄ or h _{5 to} h ₈ ) between the lower surface of the body and the substrate surface at at least four corners or four sides of the body 1 of A are measured. Then, each value of h _{1 to} h ₄ or h _{5 to} h ₈ is
It is confirmed whether or not it is within the permissible range of the optimum value h ₀ according to the above-mentioned definition known in advance, and if it is, it means that the soldering is correctly performed.

If the number of measurement points is the same, it is possible to measure the size of the gap between the lower surface of the body and the surface of the substrate more accurately by keeping the distance from each other as much as possible. Therefore,
As the data to be obtained, it can be said that the data h _{1 to} h ₄ obtained at the four corners have higher measurement accuracy than the values h _{5 to} h ₈ obtained at the four sides of the BGA shown in FIG. . Therefore, it is desirable to measure the h value at the four corners of the BGA.

FIG. 2 shows an example of a method for measuring the h-value, which is a view of the BGA body 1 mounted on the substrate 2 as seen in FIG. 5 and the like, as seen from a direction parallel to the surface of the substrate 2. is there. The body 1 of the BGA has a peripheral edge, but the reading of the upper dial gauge 20 with respect to an arbitrary reference point in the vertical direction at this edge (thickness t) is A, and then at the same height of the dial gauge 20. If the reading of the upper surface of the substrate 2 is B, then h = A−B−t.

Next, the second method of the present invention will be described. FIG. 8 is a perspective view showing a BGA mounted and soldered on a substrate 2 by the method of the present invention. 1 is a BGA body, 2 is a substrate, 11 is solder, and 12 is provided at a position corresponding to a BGA terminal. Pads on substrate 2, 13 is BGA
The marks 14 are provided at the four corners of the edge of the body 1, and the marks 14 are provided at the positions of the substrate corresponding to the BGA marks 13.

Next, a soldering inspection method for the BGA thus mounted will be described. FIG. 9 is a diagram showing a portion of the board 2 on which the BGA of FIG. 8 is mounted, viewed along the board surface. Now set the microscope 4 to the C position and mark 1
Focus on 3. Next, the microscope is horizontally moved to the position D, and the mark 14 on the substrate is similarly focused. These marks are sufficiently contrasted with the background color that the microscope can be easily focused.

If the displacement between the C position and the D position in the height direction of the microscope is observed by a scale in the height direction of the microscope or a preset displacement meter, the height difference between the marks 13 and 14 is obtained. be able to. Since the thickness t of the edge of the body 1 of the BGA is known, if t is subtracted from the value of the height difference between the marks 13 and 14 obtained above, the lower surface of the body 1 of the BGA and the upper surface of the substrate 2 are The size h of the gap can be calculated, and this h
And the optimum value h ₀ of h when soldering is successful, which is obtained in advance by experiments or the like, the quality of this soldering can be easily determined.

If the marks 13 and 14 are provided at three or more locations on the body 1 of the BGA and the board corresponding thereto, the body 1 of the BGA is inclined with respect to the board 2 as shown in FIG. The BGA body 1 has a rectangular shape and more accurate measurements can be made if the measurement points are separated from each other. Corresponding to this, four marks 14 are provided on the board 2 at four corners of the body 1 so as to measure at four points, respectively, so that more accurate solder inspection can be performed.

Further, by providing such marks 13 and 14, mechanical visual recognition is facilitated by the above-mentioned principle, and mechanization of BGA soldering inspection can be easily carried out. In FIG. 8, the mark 13.1
Although 4 shows a circular shape, it goes without saying that a shape other than a circular shape such as a rectangular shape or a triangular shape will also serve the purpose.
However, when recognizing with the visual recognition device, the marks 13 and 14
It is desirable for signal processing to have no directivity, that is, a circular mark.

[0018]

As described above, according to the first method of the present invention, the size h of the gap between the lower surface of the BGA body 1 and the surface of the substrate 2 is measured and compared with the reference value h ₀ to obtain the solder. It is possible to easily inspect the quality of soldering of the BGA to the substrate 2 without depending on the soldering conditions and the like and without using an expensive measuring device.

According to the second method of the present invention, since the marks 13 and 14 are provided, the height of each mark can be easily known with a microscope, and the soldering inspection can be performed easily and accurately. Can be tightened. Further, it is possible to easily inspect the quality of soldering of the BGA to the substrate 2 without using an expensive measuring device, easily perform image recognition, and mechanize the soldering inspection.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing the BG using the dial gauge according to the embodiment of the present invention.
It is a figure showing the method of measuring the size of the crevice between the substrate of A.

FIG. 3 is a perspective view of the BGA viewed from the lower side (terminal side) of the body.

FIG. 4 is a perspective view showing a part of a substrate on which a BGA is mounted.

FIG. 5 is a diagram showing a part of the BGA mounted on a substrate before soldering as seen from a direction parallel to the surface of the substrate.

FIG. 6 is a diagram showing the state after soldering as seen from the same position as in FIG. 5;

FIG. 7 is a diagram showing a state in which the body of the BGA is mounted and soldered at an angle with respect to the board surface, as viewed from a direction parallel to the board surface.

FIG. 8 is a perspective view for explaining an embodiment of the present invention.

FIG. 9 is a diagram showing a method for measuring the height between marks with a microscope according to an embodiment of the present invention.

[Explanation of symbols]

1: BGA body, 2: substrate, 4: microscope, 11: solder, 12: pad on substrate, 13: BGA body 1
Marks provided at the four corners of the edge, 14: BGA mark 13
Mark provided at the position of the board corresponding to, 20: dial gauge, H: dimensional value of the gap between the BGA lower surface before soldering and the upper surface of the board, h: dimension of the gap between the BGA lower surface and the upper surface of the board after soldering Value, h _{1 to} h ₈ : measured value of the measurement point in the dimension value of the gap between the BGA lower surface and the substrate upper surface, t:
BGA body edge thickness, A: Dial gauge reading on BGA edge, B: Dial gauge reading on board,
C: Position of the microscope when focusing on the mark 13,
D: Position of the microscope when the mark 14 is focused

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Higure 32 Miyukicho, Kodaira-shi, Tokyo Inside the Koganei factory, Hitachi Electronics Co., Ltd.

Claims (4)

[Claims] 1. A size of a gap between a board lower surface and a board lower surface at least at four corners or four sides of a body of a ball grid array (hereinafter referred to as BGA) mounted on a printed circuit board (hereinafter simply referred to as a board). A ball grid array characterized by judging whether or not the soldering between the board and the BGA is proper when the board and the BGA are correctly soldered together Soldering inspection method. 2. The BGA body according to claim 1, wherein
A soldering inspection method for a ball grid array, which comprises determining the quality of soldering between a board and a BGA by measuring a dimension of a gap between a bottom surface of a body and a board surface at a corner. 3. At least three of the top edges of the body of the BGA.
A mark is provided at a position in a color having a large contrast difference with the body, and a mark is also provided on the board on which the BGA is mounted at a position corresponding to the mark attached to the body of the BGA. By optically reading the difference in the mark position height between the BGA and the substrate, the BG
When the size of the gap between the lower part of the A body and the board surface is measured, and this is when the board and BGA are correctly soldered,
A soldering inspection method for a ball grid array, characterized in that the quality is judged based on whether or not the gap has a specific value. 4. The soldering inspection method for a ball grid array according to claim 3, wherein circular marks are provided at four corners of the body edge of the BGA and at positions corresponding to the four corners of the substrate.