JP3327417B2 - Metal mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal mask used for supplying cream solder to a through hole by printing on a printed wiring board.

[0002]

2. Description of the Related Art Flow soldering and reflow soldering are widely known as methods for soldering surface mounted components and inserted components to a printed wiring board. The flow soldering method is a method in which a molten solder is poured into a soldering portion to perform soldering, and is applied to soldering of a surface mount component and an insertion component.

[0003] The reflow soldering method is usually applied to a surface mount component, and a cream solder is applied in advance to a pad (a soldering portion), and the viscosity of the cream solder is used to fix the component. It is heated and melted by a heater and soldered.

On the other hand, in recent years, in order to increase the mounting density, a printed wiring board in which an insert component and a surface mount component are mounted together has been used. In this case, conventionally, the following soldering method has been performed in consideration of productivity.

FIGS. 6A to 6D are views for explaining the steps of soldering according to the conventional method. In FIG.
Is a printed wiring board in which through holes 12, 12, and pads 14, 14 are formed (FIG. 6A). On the upper surface (mounting surface) of the printed wiring board 10, cream solders 16, 16, 18 and 18 are supplied to the through holes 12 and 12 and the pads 14 and 14 by a printing method (FIG. 6B). .

Next, an insertion component 20 and a surface mount component 22 are mounted on the upper surface of the printed wiring board 10 (FIG. 6C). That is, the insertion component 20 is
a, 20b are inserted into the through holes 12, 12 from above and fixed. Further, the pads 22a and 22b at both ends of the surface mount component 22 are adhered to the cream solders 18 and 18 and are fixed by the viscosity of the cream solders 18 and 18 themselves.

The printed wiring board 10 on which the components 20 and 22 are mounted is heated by the heater 24 (FIG. 6D). For this reason, the cream solder 16, 1
8 is melted and then the molten solder solidifies to complete the soldering. In FIG. 6D, 16a,
16b, 18a and 18b show this solidified solder.

When the cream solders 16 and 18 are supplied by printing, a metal mask 3 as shown in FIG.
0 was used. An outer peripheral edge of the metal mask 30 is held by an aluminum frame. The metal mask 30 has openings 3 at positions corresponding to the through holes 12 and the pads 14.
2, 34 are formed. The metal mask 30 is made of, for example, stainless steel, and the openings 32 and 34 are formed by a suitable method such as punching or etching.

[0009]

Problems of the prior art Metal mask 3 conventionally used
7, the opening 32 corresponding to the through hole 12 was formed in a circular shape corresponding to the shape of the through hole 12, as is clear from FIG. Therefore, when the wire diameter of the leads 20a and 20b of the insertion component 20 is large (for example,
mm or more), there are two problems as shown in FIG.

[0010] These problems are as follows.
The cream solder 16c adheres to the tip of the lead 20a. The cream solder 16 is pushed out to the tip of the lead 20b, and the pushed cream solder 16d falls.

As a result, when the cream solders 16 and 18 are melted by the heater 24 (FIG. 6D), the leads 20a
Most of the cream solder 16c attached to the tip is absorbed into the through-hole 12 by wetting and capillary action. However, sometimes the cream solder 16c may not be absorbed by the through-hole 16, and at this time, FIG.
(B), the following problem occurs.

That is, at the tip of the lead 20a, the solder 1
6e solidifies, the solder 16e solidified at this tip
Drop out at an unexpected time, reducing the reliability of the product.
The absolute amount of the solder is insufficient, and the amount of the solder 16f in the through hole 16 is insufficient.

In order to solve these solder shortages, it is conceivable to increase the thickness of the metal mask 30 or increase the diameter of the opening. However, in this case, when the cream solder attached to the lead tip is normally sucked into the through hole due to the wetting and the capillary phenomenon, an excessive amount of solder enters the through hole. In FIG.
The solder indicated by b shows such a case.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and when soldering an inserted part to a through hole by a reflow soldering method, the amount of solder in the through hole becomes insufficient or excessive. It is an object of the present invention to provide a metal mask capable of stably supplying an appropriate amount of solder without causing any soldering, and preventing the solder adhering to the lead end from dropping and reducing the reliability of the product.

[0015]

According to the present invention, there is provided a metal mask used for supplying cream solder to a through hole of a printed wiring board by a printing method.
This is achieved by a metal mask provided with a blind portion near the center of the opening corresponding to the hole and having a diameter substantially equal to the lead diameter of the inserted component inserted into the through hole. That is, a hole having substantially the same diameter as the lead is formed in the cream solder supplied to the through hole.

[0016]

FIG. 1 is a perspective view of one embodiment of the present invention, FIG. 2 is a view showing a first half of a soldering process using the same, and FIG. 2 and 3, there is actually a surface mount component 22 similar to that described in FIGS. 6 and 8, but is omitted.

In FIGS. 2 and 3, reference numeral 50 denotes a printed wiring board having through holes 52 formed therein.
(A)). A metal mask 54 is placed on the upper surface of the printed wiring board 50, and an opening 56 of the metal mask 54,
56 is aligned with the through holes 52 of the printed wiring board 50 (FIG. 2B). And cream solder 5
After printing 8 and 58 with a squeegee (spatula), the metal mask 54 is lifted. Then, the cream solders 58, 58 are printed on the through holes 52, 52 of the printed wiring board 50 (FIG. 2C).

Thereafter, the leads 62, 62 of the axial component 60 as insertion components are inserted into the through holes 52, 52 (FIG. 3D), and reflow is performed. ((E) of FIG. 3). In this embodiment, cream solder 58 is printed using a metal mask 54 as shown in FIG.
The outer periphery of the metal mask 54 is held by an aluminum frame 64, while the blinds 6 are formed in the centers of the openings 56, 56.
6 are provided.

That is, the blind portion 66 is a disk having substantially the same diameter as the lead 62 of the component 60, and two support portions 68, 68 projecting in the circumferential direction are connected to the inner edge of the opening 56. I have. In addition, the blindfold 66 and the support 6
8 is formed at the same time when the opening 56 is formed in the metal mask 54 by punching or etching.

Since the metal mask 54 having the blind portion 66 near the center of the opening portion 56 is used, a small hole 70 is formed in the cream solder 58 entering the through hole 52 by the blind portion 66. (C)). Therefore, by inserting the leads 62 of the component 60 into the small holes 70 and inserting them, it is possible to prevent the cream solder 58 from adhering to the tips of the leads 62, 62 (FIG. 3D).

When the metal mask 54 is used, the blind portion 66 becomes an obstacle, so that the cream solder 58 hardly flows into the through hole 52. The insufficient amount of cream solder can be dealt with by increasing the thickness of the metal mask 54, increasing the area of the opening 56, or performing a printing operation twice by reciprocating not only once but also a squeegee (spatula). . For example, in this embodiment, the opening 5
1 and FIG. 2B, each side is formed in a quadrangle larger than the diameter of the through hole 52, so that the area of the opening 56 is changed by changing the length of each side. Can be easily adjusted.

[0022]

Next, a specific example to which the present invention is applied will be described with reference to FIGS. The components of the cream solder used here are as shown in Table 1 below.

[0023]

[Table 1] ──────────────────────────── Volume ratio Specific gravity Content weight ratio ─────────── ───────────────── Flux 39% 1.0 7% ───────────────────────── {Sn / Pb 61% 8.4 93%}

In the case of using this cream solder, even if a flux having a weight ratio of 7% is contained before the reflow, the flux volatilizes and disappears after the reflow, and the volume is reduced to about 61% as compared with that before the reflow. . In consideration of this, first, the amount of the cream solder necessary to obtain the shape shown in FIG. 4 after the solidification is obtained.

In FIG. 4, the volume V of the solder is defined as V _{1 which} is the volume of the cylindrical portion within the thickness of the printed wiring board.
The volume of the substantially conical portion (fillet) at both ends thereof as V _2, can be obtained by V = V ₁ + 2V _2. Here the volume V ₁ and V ₂ and V in can be obtained by the following equation.

[0026]

V ₁ = πt (R ² −r ² ) V ₂ = 2πh (R ² + R · r−2r ² ) / 3 where h: fillet height (= 0.2 mm) t: wiring board thickness ( = 1.6mm) 2R: Through-hole diameter (= 1.4mm) 2r: Lead diameter (1.0mm)

When the above values are substituted into V ₁ and V ₂ to determine the volume V, V = V ₁ + 2V ₂ = 1.35 mm ³ . Therefore, the volume V ₁ of the cream solder before reflow is
V ′ = V × 100/61 = 2.21 mm ³ Next, a specific example of the metal mask 54 for supplying the cream solder having the volume V 'will be described with reference to FIG.

The cream solder is supplied under the following conditions. x, y (length of opening of metal mask) = 2.
4,2.5 mm, Z (width of support) = 0.2 mm, H
(Metal mask thickness) = 0.3 mm, number of printings = 2 (printing depth T of cream solder at this time is assumed to be 1.0 mm).

Under the above conditions, the amount of cream solder V ″ supplied from the opening 56 is calculated as follows.

[0030]

V ″ = {xy−Z (x−2R) −πr ² } H + π (R ² −r ² ) · T = 2.25 [mm ³ ]

[0031] can be supplied in this way a = 2.25mm ³ "amount V close to = 2.21mm ^3" amount V of the necessary cream solder The use of this metal mask 54. At this time, since the supporting portion 68, which bridges the metal mask on the through hole of the printed wiring board, is very small, the cream solder wraps around at the time of printing and does not need to be taken into account in the calculation. In the above embodiment, two support portions 68 for holding the blindfold portions 66 are provided, but three or more support portions may be provided radially.

[0032]

According to the first aspect of the present invention, as described above, the blind portion having a diameter substantially equal to the lead diameter near the center thereof is provided in the opening of the metal mask corresponding to the through hole. When the lead is inserted into the through hole, the solder paste hardly adheres to the tip of the lead and is hardly pushed out.

Therefore, the leads are always soldered with an appropriate amount of cream solder, and the amount of solder after reflow does not become insufficient or excessive. Also, there is no danger that the solder attached to the tip of the lead will fall and reduce the reliability of the device.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view of a first half of a soldering process using the same.

FIG. 3 is an explanatory diagram of the latter half as well.

FIG. 4 is a sectional view of a soldering portion.

FIG. 5 is a diagram showing an opening of a metal mask and a supply state of cream solder.

FIG. 6 is an explanatory view of a conventional soldering process.

FIG. 7 is a perspective view of a conventional metal mask.

FIG. 8 is an explanatory diagram of a problem with the conventional method.

[Explanation of symbols]

 Reference Signs List 50 printed wiring board 52 through hole 54 metal mask 56 opening 58 cream solder 60 insertion part 62 lead 66 blindfold 68 support

Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B41N 1/24 B41C 1/14 H05K 3/34 505 H05K 3/12 610

Claims (2)

(57) [Claims] 1. A metal mask used for supplying cream solder to a through hole of a printed wiring board by a printing method. The metal mask is located near the center of an opening corresponding to the through hole and inserted into the through hole. A metal mask provided with a blind portion having a diameter substantially equal to a lead diameter of an insertion part. 2. The metal mask according to claim 1, wherein said blind portion extends radially from a peripheral edge thereof and is held by a plurality of support portions connected to an inner edge of said opening.