JP2000164772A - Auxiliary printed wiring board for area array package ic, ic test method, and repairing method of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an auxiliary printed wiring board which enables a spare area array package IC to be mounted without producing solder bridges or solder balls when pads are damaged or come off when a surface-mounted part is dismounted from a printed wiring broad, a repairing operation to be carried out for a printed wiring board by the use of a strap wiring, and ICs and a printed wiring board to be tested keeping the ICs mounted on the wiring board. SOLUTION: An area array package IC auxiliary printed wiring board 20 is used being sandwiched in between an area array package IC 12 equipped with a large number of connection terminals arranged two-dimensionally nearly like grids and a printed wiring board 10 surface-mounted with the package IC 12, where the auxiliary printed wiring board 20 is equipped with a board larger than the package IC 12, a large number of through holes 24 bored in the wiring board 2 at positions corresponding to the connection terminals of the IC 12, a large number of auxiliary pads 26 formed on the one surface of the board 20 and located outside the package IC 12, and a wiring pattern that connects the auxiliary pads 26 to the through-holes 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auxiliary printed wiring board for testing an IC or a printed wiring board with an area array package IC mounted on the printed wiring board or for repairing the printed wiring board. The present invention relates to an IC test method using the same and a method for repairing a printed wiring board.

[0002]

2. Description of the Related Art In recent years, devices using electronic circuits have been reduced in size and weight. Therefore, it is required to increase the mounting density of an IC, an LSI, a hybrid IC, or the like (hereinafter simply referred to as an IC).

[0003] In order to meet such demands, ICs
A BGA (Ball Grid Array) in which connection terminals of a package are arranged in a grid by using ball-shaped protrusions is conventionally known. A package having the surface-mounting connection terminals two-dimensionally arranged in a lattice like this is called an area array package.

[0004]

When such an area array package IC is mounted on a printed wiring board, connection terminals are hidden between the package and the printed wiring board. This makes it impossible to test the IC. On the other hand, if there is a defective component, it is necessary to remove the defective component from the printed wiring board and replace it. However, when the component is removed, the connection pads of the printed wiring board may be damaged and fall off.

[0005] In the package mounting state, a surface mount type component (SMD, Su
In the case of rface mounting device), the lead of the new part to be replaced is soldered to the pad except for the broken and dropped pad by hand using thread solder and a soldering iron, and then the broken and dropped pad The lead can be repaired by connecting the lead to be connected to the pad to a necessary portion with a strap cloth (a thin wire coated with insulation and also called a jumper wire).

It is also possible to directly test (probing) a test probe by contacting the exposed lead terminal with a test device to test an IC or a printed wiring board. However, this cannot be done in the case of an area array package IC in which the terminals and leads are not exposed to the outside in the mounted state.

That is, when mounting such a new IC for replacement, usually, a solder paste is supplied to all the connection pads of the printed wiring board at once using a screen printing mask, and the new IC is mounted. Because of the reflow soldering, it is difficult to prevent the solder paste from being supplied only to the damaged pad. When the solder paste is supplied to the position of the damaged pad and reflowed (melted), the solder moves around and generates a solder bridge connecting circuit patterns or a solder ball, thereby causing a defect. Cause.

Further, in this IC, since the connection terminals are located on the lower surface (bottom surface) of the package, it is impossible to perform the repair using the strap wiring as described above. Similarly, since the probe cannot be brought into direct contact with the connection terminal, the IC cannot be tested.

The present invention has been made in view of such circumstances, and does not generate a solder bridge or a solder ball when a pad is damaged or falls off when a surface-mounted component is removed from a printed wiring board. It is possible to mount a replacement area array package IC, and to perform repair using strap wiring, and
It is a first object of the present invention to provide an auxiliary printed wiring board which enables a test of an IC or a printed wiring board with C mounted.

An IC using the auxiliary printed wiring board
A second object is to provide a test method. It is a third object of the present invention to provide a method for repairing a printed wiring board using the auxiliary printed wiring board.

[0011]

According to the present invention, a first object is to provide a circuit between an area array package IC having a large number of connection terminals arranged two-dimensionally in a substantially lattice pattern and a printed wiring board on which this IC is surface-mounted. An auxiliary printed wiring board for an area array package IC used sandwiched between
A substrate larger than the package of C, and the IC of the substrate
A large number of through holes formed at positions corresponding to the respective connection terminals, a large number of auxiliary pads formed on one surface of the substrate and located outside the package of the IC, and the auxiliary pad and the through hole. An area array package IC comprising a wiring pattern to be connected.
Auxiliary printed wiring board for

As a substrate of the auxiliary printed wiring board, a flexible printed wiring board is suitable, but FR-4 (NEMA symbol, J) using a glass cloth epoxy material having a thickness of 0.1 mm.
(Equivalent to IS symbol GE4F)
The following may be preferable.) A hard substrate may be used. It is desirable that the surface of the auxiliary printed wiring board or both the front and back surfaces be covered with an insulating layer except for lands and pads. When a flexible printed wiring board is used for the substrate, the surface is usually covered with a cover lay, and this serves as an insulating layer.

When the pad diameter (diameter) of the printed wiring board is about 0.5 mm, the inner diameter of the through hole is smaller than this, and the outer diameter (diameter) of the land at the upper and lower ends of the through hole is less than 0 mm. It is desirable to increase the size by 0.1 to 0.2 mm. The wiring pattern needs to be formed so as not to contact other through holes, may be formed between the through holes, or may be formed using both the front and back surfaces of the board, or the wiring pattern may be formed on the inner layer as a multilayer board. May be formed. In this case, front and back circuit patterns are connected by through holes and via holes as necessary.

By using this auxiliary printed wiring board, a test can be performed by bringing a test probe into contact with an auxiliary pad while the IC is surface-mounted. That is, this auxiliary printed wiring board is fixed at a predetermined position where the through-holes match the pads of the printed wiring board using an adhesive or the like, and the solder paste is supplied to the lands of each through-hole using a metal mask or the like from above. Then, the IC may be mounted and reflow soldering may be performed.

In order to repair a printed wiring board in which a pad is damaged or dropped, an IC is reflow-soldered as described above, and an auxiliary pad corresponding to the defective pad is fixed at a predetermined position using a strap wiring. Just connect it to. For example, when connecting the auxiliary pad to a lead of another electronic component with a lead, the end of the strap wiring may be bent into a key shape, hooked, and soldered to this lead. When connecting to a through-hole, it may be inserted into this through-hole together with the lead of another component and soldered.

[0016]

After the auxiliary printed wiring board is fixed at a predetermined position on the printed wiring board, a solder paste is supplied from above the auxiliary printed wiring board, the IC is mounted thereon, and then the reflow is performed. )
It enters the through hole by capillary action. The molten solder flows into the gap between the pad of the printed wiring board and the land below the through hole through the through hole. The gap between the land on the through hole and the connection terminal of the IC is filled. Therefore, the pads of the printed wiring board and the connection terminals of the IC are connected via the through holes and the solder.

A land below the through hole of the auxiliary printed wiring board is opposed to a position where the pad of the printed wiring board is damaged or falls off. Therefore, even if the reflowed molten solder flows into the through-hole and reaches the lower end of the through-hole, it is retained in the through-hole by capillary action, and adheres to the land below the through-hole due to surface tension and becomes There is no scattering. Therefore, the molten solder does not move on the surface of the printed wiring board to generate a solder bridge or a solder ball.

[0018]

FIG. 1 is an exploded perspective view of one embodiment of the present invention.
2 is an enlarged cross-sectional view of a part thereof, FIG. 3 is a cross-sectional view showing a normal mounting state, FIG. 4 is a cross-sectional view showing a mounting state when a pad of a printed wiring board is dropped off, and FIG. FIGS. 6 and 7 are explanatory diagrams of an IC test method using the auxiliary printed wiring board, and FIG. 7 is an explanatory diagram of a printed wiring board repairing method.

In these figures, reference numeral 10 denotes a multilayer printed wiring board, and 12 denotes an area array package IC.
The IC 12 has a large number of projecting connection terminals 14 arranged in a lattice on the lower surface thereof. On the surface (upper surface) of the printed wiring board 10, a large number of pads 16 arranged in a grid pattern corresponding to the connection terminals 14 of the IC 12 are formed. The pad 16 is connected to an inner layer circuit formed on the printed wiring board 10, a via hole, a through hole, or the like.

Reference numeral 20 denotes an auxiliary printed wiring board,
Larger than package 2. The substrate 22 of the auxiliary printed wiring board 20 is preferably made of a flexible printed wiring board or a hard board of NEMA symbol [FR-4] using a thin (for example, about 0.1 mm thick) glass cloth epoxy material. The substrate 22 has a large number of through holes 24 arranged in a lattice pattern corresponding to the positions of the connection terminals 14 or the pads 16, and auxiliary pads located outside the through holes 24, that is, on the outer peripheral side of the substrate 20. 2
6 and a circuit pattern 28 for connecting these auxiliary pads 26 to the through holes 24 are formed.

The number of auxiliary pads 26 is equal to the number of connection terminals 14 or through holes 24. These through holes 24, auxiliary pads 26, and circuit patterns 28 can be formed by using a known photoetching method or plating method. For example, first, copper foil is adhered to both surfaces of the substrate 22, and the lands 30, 30 of the through hole 24, the auxiliary pad 26, and the
8 are formed. Then, after processing the small holes of the through holes 24, the small holes and the lands 30 and 30 are covered with a plating resist, and after electroless plating, copper plating is performed.
Form 2

The circuit pattern 28 for one through hole 24 is different from the other through holes 24 arranged in a lattice.
Are connected to the corresponding auxiliary pads 26 between the lands 30. The circuit pattern 28 is covered with an insulating layer (not shown) such as a coverlay. The insulating layer is sufficiently thin so that the IC 12 does not come into contact with the lower surface of the package when the IC 12 is mounted as shown in FIG. .

The outer diameter (diameter) A of the land 30 of the through hole 24 is larger than the diameter B of the pad 16 of the printed wiring board 10 as shown in FIG. It is desirable that the diameter be smaller than the diameter B. For example, if the pad diameter B is 0.5 mm, the land diameter A
Is 0.1 to 0.2 mm larger than the pad diameter B, and the inner diameter C of the through hole is smaller than the pad diameter B by 0.1 to 0.2 mm. By setting the diameter in this way, the molten solder stably adheres to the pad 16 at the time of reflow, as described later, to improve the connection reliability. In addition, when the pad 16 is dropped, the molten solder passes through the through hole. 24, and the effect of restricting the movement by holding it securely is increased.

When using this auxiliary printed wiring board 20, first, as shown in FIG. 6A, it is fixed to the mounting position of the IC 12 using an instant adhesive or the like. At this time, it goes without saying that the through-hole 24 is positioned so as to overlap the pad 16 of the printed wiring board 10 (see FIG. 2). Next, a metal mask 34 is overlaid on the auxiliary printed wiring board 20, and a solder paste 38 is supplied onto each through hole 24 using a squeegee 36 as shown in FIG. 2B (see FIG. 2).

After an appropriate amount of solder paste 38 is placed in each through hole 24, the connection terminals 14 of the IC 12 are aligned with the through holes 24, and the IC 12 is placed as shown in FIG. 6C. Then, as shown in FIG. 2 (D), the solder paste 38 is placed in a reflow furnace and heated to melt the solder paste 38. As shown in FIG. 3, the molten solder 38A flows into the through hole 24 by capillary action, filling the gap between the pad 16 of the printed wiring board 10 and the land 30 below.
Further, the inside of the through hole 24 and the connection terminal 14 of the IC 12
And the gap between the upper land 30 is filled.

Further, in the through hole 24 facing the position where the pad 16 of the printed wiring board 10 has fallen off, as shown in FIG.
With the surface tension of 0, the molten solder 38A causes the lower land 3
0 is held on the lower surface. Therefore, the molten solder 38A does not move to the surroundings, and a solder bridge connecting between the surrounding pads 16 and between circuit patterns is not formed. Similarly, there is no risk of forming solder balls.

After mounting the IC 12 in this manner, the IC 1
2 and FIG.
As shown in (E), the test probe 4 is attached to the auxiliary pad 26 of the auxiliary printed wiring board 20 exposed outside the IC 12.
0 may be contacted. As a result, connection terminal 1 of IC 12
The test can be carried out even if 4 is not exposed to the outside.

If the pads 16 of the printed wiring board 10 are damaged or fall off, the IC 12 is mounted using the auxiliary printed wiring board 20 in the same manner as in FIG. 6, and then the strap wiring 42 shown in FIG. Repair using That is, the through hole 2 facing the broken or dropped pad 16
Find the auxiliary pad 26 connected to 4 in advance,
One end of the strap wiring 42 is manually soldered to the auxiliary pad 26. Then, the other end of the strap wiring 42 may be hooked to a predetermined connection point, for example, a lead of another mounting component 44 and soldered. In this case, an unnecessary portion of the auxiliary printed wiring board 20 may be cut out with a knife or the like.

[0029]

As described above, according to the first aspect of the present invention, the through holes provided at the positions corresponding to the connection terminals of the area array package IC, the auxiliary pads located outside the IC package, and the through holes and the auxiliary Since this is an auxiliary printed wiring board provided with a circuit pattern for connecting to a pad, the auxiliary printed wiring board is sandwiched between the IC and the printed wiring board.
By mounting C, the IC can be mounted without generating solder bridges or solder balls even if some pads of the printed wiring board are damaged or dropped, and repair using strap wiring In addition, it is possible to test an IC or a printed wiring board with the IC mounted.

If the flexible printed wiring board is used as the substrate, the auxiliary printed wiring board can be made sufficiently thin and unnecessary portions can be easily cut off, which is convenient.

If the inner diameter of the through hole is smaller than the pad diameter of the printed wiring board and the land diameter of the through hole is larger than this pad diameter, the capillary effect of the through hole can be effectively used and the pad is missing. In this case, the molten solder can be reliably held on the land of the through hole (claim 3). The circuit pattern of the auxiliary printed wiring board may be formed on the front surface (claim 4), but may be formed using the front surface and the back surface. In this case, if a through hole or a via hole is provided at an appropriate position. Good (claim 5). According to claim 6, a method of testing an IC using the auxiliary printed wiring board is obtained, and according to claim 7, a method of repairing the printed wiring board is obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of one embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a part thereof.

FIG. 3 is a sectional view showing a normal mounting state.

FIG. 4 is a diagram showing a mounting state when a pad is missing;

FIG. 5 is an explanatory diagram of dimensions of each part.

FIG. 6 is an explanatory diagram of an IC test method.

FIG. 7 is an explanatory view of a method for repairing a printed wiring board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Printed wiring board 12 IC 14 Connection terminal 16 pad 20 Auxiliary printed wiring board 22 Substrate 24 Through hole 26 Auxiliary pad 28 Circuit pattern 30 Land 32 Plating layer 34 Metal mask 38 Solder cream 38A Melt solder 40 Test probe 42 Strap wiring

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/34 510 G01R 31/28 S

Claims (7)

[Claims] 1. An area array package IC having a large number of connection terminals two-dimensionally arranged in a substantially lattice shape, and the IC
Is an auxiliary printed wiring board for an area array package IC which is used sandwiched between a printed wiring board to be surface-mounted, and a substrate larger than the package of the IC and a connection terminal of each of the ICs of the substrate. A plurality of through holes formed at corresponding positions, and the I-hole formed on one surface of the substrate;
An auxiliary printed wiring board for an area array package IC, comprising: a number of auxiliary pads located outside a package of C; and a wiring pattern connecting the auxiliary pads and through holes. 2. The auxiliary printed wiring board for an area array package IC according to claim 1, wherein the substrate is a flexible printed wiring board. 3. The printed circuit board according to claim 1, wherein the inner diameter of the through hole is smaller than the pad diameter of the connection terminal of the printed wiring board, and the land outer diameter of the through hole is larger than the pad diameter of the connection terminal of the printed wiring board. 2. Auxiliary printed wiring board for area array package IC. 4. The auxiliary printed wiring board for an area array package IC according to claim 1, wherein at least a part of the wiring pattern is formed on the surface of the substrate so as not to contact another through hole. . 5. The auxiliary print for an area array package IC according to claim 1, wherein at least a part of the wiring pattern is formed on a back surface of the substrate and connected to the auxiliary pad by a through hole or a via hole. Wiring board. 6. The area array package IC after fixing the auxiliary printed wiring board according to any one of claims 1 to 5 at a predetermined position of the printed wiring board and supplying a solder paste from above to a land of a through hole. And carrying out reflow soldering and contacting a test probe with an auxiliary pad of an auxiliary printed wiring board to perform a test.
C test method. 7. The area array package IC after fixing the auxiliary printed wiring board according to any one of claims 1 to 5 at a predetermined position of the printed wiring board and supplying a solder paste from above to a land of a through hole. And reflow soldering, and connecting the auxiliary pad of the auxiliary printed wiring board to another predetermined connection portion using a strap wiring.