JPH11251725A - Printed wiring board and method for soldering using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a solder bridge from occurring even with a smaller solder- drawing land. SOLUTION: In a QFP(quad flat package) IC mounting region 12, soldering lands 13 are formed in square frame, and at three corners of the mounting region 12, solder drawing lands 16 and 16 of right-angled isosceles triangle are formed with a gap 17 in between, while oblique lines facing each other with each solder-drawing land 16 opened with a solder-drawing hole 18. Related to a QFP IC1, temporarily fixed to the mounting region 12 with an adhesive tape 22, it is allowed to pass a flow solder part where a molten solder has erupted with a head part 15 of the printed wiring board 10 where no solder drawing land exists at top side. An excessive molten solder after the soldering land 13 and the lead 4 are soldered is taken to the solder-drawing land 16 and pulled into the solder-drawing hole 18. Since the solder-drawing hole pulls in a molten solder, the solder-drawing land may be set small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and a soldering method using the same, and more particularly to a technique for preventing a solder bridge in a dip (immersion) soldering method. The present invention relates to a technology effective for mounting a semiconductor integrated circuit device (hereinafter, referred to as an IC) having a package (hereinafter, referred to as a QFP).

[0002]

2. Description of the Related Art An IC having a QFP (hereinafter referred to as a QFP / I
Called C. ) Is a thin, surface-mount type package with a low mounting height, and because it has leads on all sides of the resin sealing body, the number of leads can be set large. It is coming. And QFP
・ With the high integration and multi-function of IC, QFP ・ I
As the number of leads of C increases, the pitch between leads has become smaller. Therefore, when the QFP · IC is soldered to the printed wiring board by a flow soldering method, which is an example of a dip-type soldering method, the possibility of occurrence of a solder bridge is increasing.

Therefore, Japanese Patent Application Laid-Open No. Hei 5-315733 proposes a printed wiring board for preventing the occurrence of a solder bridge in a flow soldering method. That is, in this printed wiring board, the side soldering lands are separately provided between the front soldering land group and the rear soldering land group inclined with respect to the soldering proceeding direction. A rear soldering land is provided separately at the rear end, and further, an independent thin soldering land is provided between the side soldering lands and between the rear soldering lands.

[0004] In this printed wiring board, the solder is taken up by the solder drawing land and the solder flows easily, so that it is possible to prevent the solder from rising greatly. Furthermore, since the thin soldering lands independent of each other are provided between the soldering lands provided at the four corners, the solder that is not absorbed by the soldering lands can be absorbed by the thin soldering lands, and between the soldering lands. The occurrence of a solder bridge can be prevented.

[0005]

However, in the above-mentioned prior art, it is necessary to increase the size of the soldering land in order to reliably prevent the occurrence of the solder bridge. Will be hindered. In other words, if the area of the soldering land is set small in order to increase the mounting density, the possibility of the occurrence of a solder bridge increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a printed wiring board which can reliably prevent the occurrence of a solder bridge between adjacent soldering portions even when the area of a soldering land is set small. .

[0007]

In a printed wiring board according to the present invention, a plurality of soldering portions are arranged in a soldering object mounting area set on one main surface of a main body. In a printed wiring board in which soldering lands are formed at at least one end of a group of rows, a soldering hole is formed in the soldering land.

For example, in the method of flow soldering of the QFP / IC to the printed wiring board, the QFP / IC is temporarily fixed to the mounting area of the soldering object by an appropriate means such as an adhesive, and is passed through the solder flow portion. You. Since the molten solder adheres to the soldering portion and the lead of the QFP / IC and solders the both, a solder pile portion is formed between the soldering portion and the lead. Q with the movement of the printed wiring board
At the moment when the FP / IC is separated from the solder flow portion, the excess molten solder is taken up by the solder drawing land and the solder drawing hole, and the solder bridge portion is excessively raised to form a solder bridge. Is prevented.

According to the above-described means, since the soldering hole is formed in the soldering land, excess molten solder can be sufficiently drawn in by the soldering hole, so that the area of the soldering land is set small. As a result, the mounting density of the printed wiring board can be increased.

[0010]

FIG. 1 is an exploded perspective view showing a case where a QFP IC is mounted on a printed circuit board according to an embodiment of the present invention. 2A and 2B show the flow soldering method, in which FIG.
(B) is an enlarged partial cross-sectional view showing a soldered portion, (c).
FIG. 4 is an enlarged partial cross-sectional view showing the function of a soldering hole.

In this embodiment, the printed wiring board according to the present invention is configured such that the QFP IC 1 is mounted by soldering by a flow soldering method. The QFP IC 1 to be soldered includes a resin sealing body 3 and a QFP 2 including a plurality of leads 4. That is, the resin sealing body 3 of the QFP 2 is formed in a substantially square flat plate shape, and a plurality of leads 4 protrude from four side surfaces of the resin sealing body 3 and are aligned in a line. The lead 4 protruding from the resin sealing body 3 is bent in a gull wing (gull wing) shape.
The lower end surface (mounting surface; seating plane) of the group of terminal flat portions 5 is slightly lower than the lower end surface of the resin sealing body 3 to form the same surface.

The printed wiring board 10 includes a main body 11 having an insulating property. The main body 11 is formed in a rectangular flat plate shape of a desired size using an insulating material such as an epoxy resin impregnated with glass. A QFP / IC mounting area 12 as a soldering object mounting area is provided at a desired portion on a mounting surface (hereinafter referred to as a front side) of the main body 11.
-It is set in advance to a substantially square shape corresponding to the planar shape of IC1.

The QFP / IC mounting area 12 of the main body 11 has a plurality of soldering lands 13 as soldering portions.
They are arranged in a substantially square frame shape so as to correspond to the four rows of leads of the P · IC1. Each soldering land 13
Is formed in a square slightly larger than the size of the terminal flat portion 5 of the lead 4. The pitch between the adjacent solder lands 13 in each row corresponds to the pitch between the leads 4 of the QFP IC 1. An electric wiring 14 formed on the surface or inside of the main body 11 is electrically connected to each soldering land 13. The electric wiring 14 connects each soldering land 13 to another soldering land 13 or a printed wiring board. The printed wiring board 10 is electrically connected to other electrical components mounted on the printed wiring board 10 and external terminals disposed at the end of the printed wiring board 10.

At one of the four corners of the square QFP / IC mounting area 12, a leading portion 15 having no soldering land is set, and at the other three corners, a soldering land 16 is arranged. Has been established. That is,
The soldering lands 16 are arranged at the ends of the row of the group of soldering lands 13 except the leading end 15. The soldering lands 16 are each formed in the shape of a thin plate having a right-angled isosceles triangle, and a pair of soldering lands 16 are combined at three corners to form a square as a whole. The oblique sides of the soldering lands 16 and 16 are opposed to each other on both sides of a diagonal extension of the QFP / IC mounting area 12 with a gap 17 for separating the solder pile portion therebetween.

A soldering hole 18 is formed at the center of each soldering land 16 so as to penetrate in the thickness direction of the main body 11. A soldering portion 19 having good solderability is formed on the inner peripheral surface of the soldering hole 18, and the soldering portion 19 is connected to the soldering land 16. Opposite solder pulling portions 20 are formed at portions corresponding to the solder pulling portions 19 on the back side opposite to the mounting surface of the main body 11, and the opposite solder pulling portions 20 are connected to the front side solder pulling lands. 16 are formed. The inner diameter D of the soldering portion 19 corresponding to the inner diameter of the soldering hole 18 is 35% to 8% of the thickness t of the main body 11.
It is set to 0%. For example, when the thickness of the main body 11 is 1.
When it is set to 6 mm, the inner diameter of the soldering hole 18 is set to 0.6 mm to 1.2 mm.

Solder land 16, solder hole 18
The soldering portion 19 and the opposite soldering land 16 of
It is formed together with the soldering lands 13 and the electric wires 14 by a conductor forming method such as a screen printing method, a lithography and an etching method. The soldering land 16 may be electrically connected to the electric wiring 14 or may be insulated.

On the surface of the main body 11, a non-wetting surface portion 21 formed by using a solder resist having a property (non-affinity, water repellency) that does not wet the solder material is adhered. 21 is a soldering land 13 or an electric wiring 1
4 and the entire area around the portion where the solder pile portion such as the soldering land 16 is formed. At one corner of the four corners of the QFP / IC mounting area 12 on the surface of the main body 11 where the soldering land 16 is not provided, the non-wetting surface 21 is formed widely.

Next, the soldering method according to one embodiment of the present invention is applied to the printed wiring board 10 having the above-described structure.
A description will be given of a flow soldering method of the FP · IC 1.

QFP · I for Printed Wiring Board 10
In the flow soldering method C1, a heat-resistant adhesive tape 22 is adhered to the center of the QFP / IC mounting area 12 of the printed wiring board 10 as shown in FIG. The main surface of the resin sealing body 3 of the IC 1 facing the mounting surface is adhered, so that the QFP IC 1 is temporarily fixed to the printed wiring board 10.

As shown in FIG. 2A, the flow soldering method is performed on the printed wiring board 10 with the front side, which is the side where the QFP IC 1 is temporarily fixed, facing downward. Flow part 2 formed inside the solder bath
3 passed. That is, the molten solder 24 is stored in the solder tank, and the solder flow portion 23 having a mountain shape is formed by being spouted from the slit type nozzle 25. The paper is conveyed so as to pass through the unit 23. At this time, the printed wiring board 10 has a QFP / IC
It is transported in the diagonal direction of the mounting area 12 (the X arrow direction in FIG. 1).

When the printed wiring board 10 moves the solder flow section 23 at a speed specified in advance along the direction of soldering, the molten solder 24 forms the solder land 13 and the lead 4.
2B, a solder pile 26 is provided between the soldering land 13 and the lead 4.
Is formed as shown in FIG. At this time, the molten solder 24 in contact with the non-wetting surface portion 21 formed between the adjacent soldering lands 13 is water-repellent.
Soldering lands 1 unless adjacent
No solder bridge is formed between 3 and 13.
Incidentally, the supply amount of the molten solder 24 to the soldering lands 13 is controlled by the transport speed of the printed wiring board 10 and the like.

At the moment when the QFP IC 1 is separated from the solder flow portion 23 with the movement of the printed wiring board 10, the excess molten solder 24 is removed from the solder provided at the end of the row of each soldering land 13 group. The solder lands 26 are prevented from being raised by the pulling lands 16 to form a solder bridge due to a raised state. On this occasion,
A pair of right-angled isosceles triangular soldering lands 16, which are opposed to each other, are separated by gaps 17, so that the swelling of the molten solder 24 is divided by the gaps 17. The takeover action will be effectively exerted.

Further, since the excess molten solder 24 drawn by each of the solder pulling lands 16 is drawn into the solder pulling hole 18, the formation of a solder bridge is more reliably prevented. At this time, the soldering hole 18 has a sufficient capacity and an excessive amount of molten solder 24 due to a capillary phenomenon.
Therefore, even when the area of the soldering land 16 is set small, the shortage of the molten solder 24 can be sufficiently reduced by the reduced size of the soldering land 16. Can be supplemented.

Here, if the inner diameter D of the soldering hole 18 is set outside the range of 35% to 80% of the plate thickness t of the main body 11, the amount or action of the molten solder 24 drawn in by the soldering hole 18 is reduced. It has been discovered by experiments of the present inventor that the solder bridge may be insufficient and a solder bridge may be formed. If the inner diameter D of the soldering hole is less than 35% of the plate thickness t of the main body 11, the capacity of the soldering hole becomes small, so that the volume of the molten solder that can be drawn in by the soldering hole is insufficient. When the inner diameter D is small,
There is a tendency that the soldering hole is clogged by air bubbles or the drawing force is reduced depending on the viscosity of the molten solder. Conversely, the inner diameter D of the soldering hole is equal to the thickness t of the body 11.
If it exceeds 80%, the opening area of the soldering hole is too large and the capillary phenomenon of the soldering hole does not function effectively, so that a phenomenon occurs in which the molten solder is not drawn into the soldering hole.

As described above, according to the present embodiment, since the soldering hole is formed in the soldering land, excess molten solder can be sufficiently drawn in by the soldering hole. Occurrence can be reliably prevented. Therefore, since the area of the soldering land can be set small, the mounting density of the printed wiring board can be increased.

It should be noted that the present invention is not limited to the above-described embodiment, but may be modified without departing from the scope of the invention.
It goes without saying that various changes can be made.

For example, the soldering land is not limited to a right isosceles triangle, but may be a quadrangle or a polygon.

Instead of using the flow soldering method, another dip-type soldering method may be used.

The object to be soldered is not limited to QFP / IC,
QFJ / IC (quad flat / J-lead package / IC) and other four-sided surface mount package / IC with leads in four directions, SOP / IC (small outline package / IC) etc. Mounted package / IC, and DIP / IC
It may be an insertion type package / IC having an insertion lead such as a (dual in-line package / IC), or may be a transistor or other electric parts without being limited to the IC.

[0030]

As described above, according to the present invention,
By opening a soldering hole in the soldering land, excess molten solder can be drawn in by the soldering hole during the dip-type soldering method, so even if the area of the soldering land is set small, excess solder can be removed. It is possible to sufficiently prevent the occurrence of solder bridges by absorbing sufficiently, and as a result, it is possible to improve the mounting density of the printed wiring board.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a case where a QFP / IC is mounted on a printed wiring board according to an embodiment of the present invention.

FIG. 2 shows the flow soldering method, in which (a)
FIG. 3 is a partially cutaway front view showing the middle thereof, (b) is an enlarged partial cross-sectional view showing a soldered portion, and (c) is an enlarged partial cross-sectional view showing the function of a soldering hole.

[Description of Signs] 1 ... QFP / IC (object to be soldered) 2 ... QFP, 3
... Resin sealed body, 4 ... Lead, 5 ... Terminal flat part, 10 ... Printed wiring board, 11 ... Main body, 12 ... QFP / IC mounting area (soldering object mounting area), 13 ... Soldering land (Soldering) 14) electrical wiring, 15: head without soldering land, 16: soldering land, 17: gap, 18: soldering hole, 19: soldering part, 20 ...
Opposite-side soldering portion, 21: non-wetting surface portion, 22: adhesive tape, 23: solder flow portion, 24: molten solder, 25: slit nozzle, 26: solder pile portion.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Mamoru Takano 1-2681, Hirosawa-cho, Kiryu-shi, Gunma Co., Ltd. (72) Inventor Hideaki Kanaya 1-2681-1, Hirosawa-cho, Kiryu-shi, Gunma, Co., Ltd. 72) Inventor Yuichi Nagase 1-2681, Hirosawa-cho, Kiryu-shi, Gunma Inside Mitsuba Co., Ltd.

Claims (3)

[Claims] A plurality of soldering portions are arranged in a soldering object mounting area set on one main surface of a main body, and a soldering land is formed at least at one end of a row of the soldering portion group. A printed wiring board according to claim 1, wherein a soldering hole is formed in said soldering land. 2. The printed wiring board according to claim 1, wherein the inside diameter of the soldering hole is set to 35% to 80% of the thickness of the main body. 3. In a state where the respective leads of the object to be soldered are in contact with the respective soldering portions, the respective soldering portions and the soldering lands are separated from the molten solder after being brought into contact with the molten solder. 2. The printed wiring board according to claim 1, wherein each of the soldering portions and each of the leads are soldered, and excess molten solder is taken up by the soldering land and the soldering hole. 3. Soldering method using.