JPH0670278U - Printed board - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a printed circuit board capable of suppressing generation of a solder bridge by narrowing a gap between the printed circuit board and a metal mask for applying solder. A soldering resistance layer 10 having a height Rh substantially equal to the height Lh of the land 2 is provided between each land 2 of a plurality of lands 2 formed in a predetermined pattern on a substrate 1.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a printed circuit board, and more particularly to a printed circuit board that is compatible with high pin count, high pin count, and narrow pitch.

[0002]

[Prior art]

 In recent years, with the downsizing of sets, the mounting density on printed circuit boards has been increasing. In particular, in flat package type semiconductor IC devices such as QFP (Quad Flat Package), there is an increasing tendency to have a large number of pins and a narrow pitch (1.0, 0.8 mm → 0.65, 0.5 mm pitch).

The QFP or the like of these IC devices is connected and mounted by soldering to a circuit or the like formed on a printed circuit board or the like. This soldering is usually done by reflow soldering. In this reflow soldering, an appropriate amount of cream solder is applied by screen printing on the land of a specified pattern on the printed circuit board, and the lead terminals such as QFP are automatically attached. After that, it is made by heating and melting in a reflow furnace.

[0004]

[Problems to be solved by the device]

 By the way, as described above, due to the recent increase in the number of pins and the narrow pitch of flat packages such as QFP, the solder connects the lead terminals in the reflow soldering process, resulting in a solder bridge causing a solder short.

This solder bridge is likely to occur between the leads unless the amount of cream solder printed on the land is accurately controlled.

FIG. 3 shows a conventional view of cream solder application to a land on a printed circuit board. As shown in FIG. 3, in the conventional cream solder application to the land, the cream solder 5 is applied to the land 2 at a predetermined position on the printed board 1 by printing through the metal mask 3. In this case, if the height of the land 2 on the surface of the printed circuit board 1 is increased to about 25 to 40 μm, the gap between the metal mask 3 serving as the mask of the cream solder 5 and the surface of the printed circuit board is increased, and as a result, The amount of cream solder printed increased, and as a result of conducting a 0.5 mm pitch QFP reflow experiment, it was found that a reflow bridge was also likely to occur.

In view of the above problems, it is an object of the present invention to provide a print substrate capable of suppressing the occurrence of reflow solder bridges by narrowing the gap between the printed substrate and the metal mask for solder application. To do.

[0008]

[Means for Solving the Problems]

 According to the present invention, according to the present invention, a soldering resistor having a height Rh substantially equal to the height Lh of the land 2 is provided between the lands 2 of the plurality of lands 2 formed in a predetermined pattern on the substrate 1. The solution is a printed circuit board characterized in that it comprises a layer 10.

[0009]

[Action]

 According to the present invention, since the soldering resistance layer (resist) 10 having substantially the same height is provided between the lands 2 for soldering the lead terminals of the flat package such as QFP, solder paste such as cream solder. The amount of printing applied to the land 2 can be precisely controlled. Therefore, it is possible to suppress the occurrence of reflow bridge even in a lead having a large number of pins and a narrow pitch.

[0010]

【Example】

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining an embodiment of the print substrate according to the present invention. According to FIG. 1, a soldering resistance layer 10 is provided in a region between the lands 2 on the printed circuit board 1, that is, in a region between the printed circuit board 1 and the metal mask 3. In this case, the height R1 of the soldering resistance layer 10 is made substantially equal to the height L1 of the land 2, so that the cream solder 2 is printed on the land 2 most stably and the bridge is reduced.

The reason will be described with reference to FIG. In FIG. 2, when the height (Rh) of the soldering resistance layer 10 is larger than the height (Lh) of the land A, the height (Rh) of the soldering resistance layer 10 is substantially equal to the height (Lh) of the land. FIG. 8 is a cross-sectional view showing Case B, and C where the height (Rh) of the soldering resistance layer 10 is smaller than the height (Lh) of the land.

As can be seen from FIG. 2, in each of the two cases of A: Lh <Rh and BC: Lh> Rh, the land of the cream solder 5 of granular powder applied onto the land 2 through the metal mask 3 is used. The amount of printing applied between the two is larger than that in the case of B. Therefore, in the case of A and C, a bridge often occurs between the leads.

The optimum condition of the height Rh of the soldering resistance layer is preferably substantially equal to the height Lh of the land as described above, but if the size (diameter) of the cream solder powder is, for example, 10 to 60 μm. For example, it is preferable that the minimum size is smaller than 10 μm in order to make it difficult to enter the space between the lands. That is, in the embodiment of the present invention, | Lh−Rh | ≦ 10 μm (minimum diameter of cream solder powder) is optimal. Also, the gap between the soldering resistance layer and the land is preferably 10 μm or less, as described above, in order to prevent the cream solder from entering the gap between the lands.

[0014]

[Effect of device]

 As described above, according to the present invention, since the resistance layer with solder 10 having a height substantially equal to the land height is provided between the lands to which the solder is applied, the amount of solder printing on the lands is reduced. Since it is precisely controlled, it is possible to solder lead terminals such as multi-pin, narrow-pitch QFP onto the land without generating a reflow bridge.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining one embodiment of a printed circuit board according to the present invention.

FIG. 2 is a schematic sectional view for explaining an optimum land height.

FIG. 3 is a schematic cross-sectional view for explaining a conventional printed circuit board.

[Explanation of symbols]

 1 Printed Circuit Board 2 Land 3 Metal Mask 5 Cream Solder 10 Solder Resistance Layer

Claims (1)

[Scope of utility model registration request] 1. A printed circuit board, characterized in that a soldering resistance layer having a height substantially equal to the height of the land is provided between each land of a plurality of lands formed in a predetermined pattern on the board. .