JPH04361589A - Soldering method of discrete part to printed wiring board and cream solder metal mask - Google Patents

Abstract

PURPOSE:To enable a discrete part to be soldered to a printed wiring board through a reflow soldering method by a method wherein the opening of a cream solder metal mask used for a double-side reflow process is carefully contrived. CONSTITUTION:A metal mask 3 provided with an opening 4 conforming to a through-hole land 2 provided to a printed wiring board 1 is prepared (a). The opening 4 concerned is formed to extend outside of a land pad 2b or a conductive part of the through-hole land 2 and into a shape excluding a part which comes into contact with the main body of a discrete part 7 (excluding leads 7). Cream solder 5 is previously applied using the metal mask 3 (c). The leads 7 of the discrete part 6 are inserted into the openings 2a of the through- hole lands 2 through the cream solder 5 by an adequate method, and then the discrete part 6 is mounted (d), (e). In this state, the discrete part 6 and the printed wiring board 1 are placed in a hot electric oven, whereby the discrete part 6 can be fixed by soldering through a reflow soldering method the same as a conventional chip part (f), (g).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for soldering discrete components such as transistors, resistors, and diodes to printed wiring boards, which are widely used in electrical products, and a metal mask for cream solder used in the method.

0002

2. Description of the Related Art Components soldered to printed wiring boards include chip components such as integrated circuits and large-scale integrated circuits, and discrete components other than chip components such as transistors, resistors, and diodes. Generally, when soldering chip components, cream solder is applied to lands for chip components on a printed wiring board, and then the chip components are mounted and fixed in a high-temperature electric furnace. For discrete components, leads are inserted into through-hole lands for discrete components, and soldering is performed from the opposite side of the printed wiring board, that is, the side from which the leads came out.

[0003] For discrete components, the leads are inserted into the through-hole lands from one side (component side) of the printed wiring board, and soldered from the opposite side (solder side).
The chip components were fixed to the solder surface. However, in recent years, as electrical components have become more multifunctional, automated, and miniaturized, the number of chip components used has increased, and as a result, chip components are now being installed not only on the solder surface but also on the component surface. This has led to the adoption of the so-called double-sided reflow soldering method.

In this case, the soldering process was performed in the following three stages. Soldering process (1) Mounting and fixing chip components on the solder surface of the printed wiring board.

Soldering process (2) Mounting and fixing of chip components on the component surface of the printed wiring board. Soldering process (3)
Mounting and fixing of discrete components on the component surface of printed wiring boards.

[0006]

However, the conventional soldering method described above, which is carried out in three steps, requires a large number of soldering steps and requires a large amount of time and cost.

[0007] Furthermore, since soldering of discrete components is performed using the reflow method similar to soldering of chip components, even if cream solder is applied to the component side of the through-hole land, reducing the amount of cream solder will lead to If the through-hole land is not properly fixed, and if the amount is increased, the cream solder will get between the discrete component and the printed wiring board, causing the discrete component to float or tilt, resulting in poor conductivity, etc. there were. The present invention solves these conventional problems, and provides an excellent printed wiring board soldering method for discrete components that uses cream solder to fix both chip components and discrete components using the reflow soldering method. , and to provide a metal mask for cream solder used in the method.

[0008]

[Means for Solving the Problems] The present invention has been made to achieve the above object, and the invention as claimed in claim 1 is directed to a land pad that is a conductive portion of a through-hole land formed on a printed wiring board, and a central a cream solder application process of applying cream solder to the outside of the land pad including the opening and excluding the part where the main body of the discrete component and the printed wiring board are in contact; and an insertion process of inserting the lead of the discrete component into the opening. and a fixing step of placing the printed wiring board together with the discrete components in a high-temperature electric bath and fixing the discrete components to the printed wiring board.

[0009] Furthermore, the invention of claim 2 is a metal mask for cream solder used in the method of the invention of claim 1,
A portion where the printed wiring board contacts the main body of a discrete component that extends to the outside including a land pad that is a conductive part of a through-hole land formed on the printed wiring board, and a lead is inserted into the central opening of the land pad. It has an opening having a shape other than

0010

[Operation] Therefore, according to the present invention, the lead of the discrete component is connected to the cream solder applied to the opening of the through-hole land by an appropriate mechanical method or a method of melting the cream solder thermally and electrically. If the inserted state is placed in a high-temperature electric bath, the discrete component can be fixedly soldered using the reflow soldering method in the same way as conventional chip components.

In particular, the cream solder applied in advance spreads to the outside, including the land pad, and is applied to all but the parts where the main body of the discrete component (other than the leads) and the printed wiring board are in contact, so that a sufficient amount of solder is applied. To properly fix the leads of a discrete component to a through-hole land using cream solder, and to prevent the cream solder from entering between the discrete component and a printed wiring board and causing the discrete component to float or tilt.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1(a) to 1(g) show the working process of a soldering method according to an embodiment of the present invention. FIG. 1(a) is a schematic diagram of the printed wiring board 1 on the component side. This printed wiring board 1 is provided with three through-hole lands 2. At the center of each through-hole land 2 are discrete components such as transistors, resistors, etc. other than integrated circuits.
An opening 2a is formed into which a lead of a discrete component such as a diode is inserted, and a land pad 2b, which is a conductive portion that is electrically connected to the lead, is formed around this opening. A resist 2c, which is an insulating coating layer, is formed around the land pad 2b.

FIG. 1(b) is a schematic diagram of the metal mask 3. The metal mask 3 has an opening 4, and cream solder 5 is applied to the required portion of the printed wiring board 1 through the opening 4.
is applied. The opening 4 is provided in a shape corresponding to the three through-hole lands 2, and has a shape in which the three through-hole lands 2 are connected. Further, this opening 4 is configured such that cream solder 5 can be applied to the center opening 2a of the through-hole land 2 and the land pad 2b to the outside of the land pad 2b. In addition, as shown in FIGS. 1(d) and 1(e), the shape is such that cream solder can be applied to the parts except for the parts where the main body of the discrete component 6 (excluding the leads 7) and the printed wiring board 1 are in contact.

FIG. 1(c) shows a state in which cream solder is applied to the printed wiring board 1 using the metal mask 3. As shown in FIG. The applied cream solder 5 has the same shape and size as the opening 4 of the metal mask 3.

FIG. 1(d) shows a printed wiring board 1 coated with cream solder 5 and a discrete component 6 mounted thereon. The lead 7 of the discrete component 6 is passed through the cream solder 5 by an appropriate method to the through-hole land 2.
into the opening 2a. For example, the thickness of the cream solder 5 may be made thin, and the lead 7 may be penetrated by mechanical force, or the contact point between the lead 7 and the cream solder 5 may be heated electrically, and the cream solder may be locally applied. Possible methods include melting 5 and penetrating it. Alternatively, the opening 2a may be left partially open and the lead 7 may be inserted through this open area.

In this state, the printed wiring board 1 and the discrete components 6 are placed in a high temperature electric bath and heated. This heating melts the cream solder 5 and fixes the leads 7 to the through-hole lands 2. At this time, since the cream solder 5 that had been applied in advance was applied over a wide area to the outside of the land pad 2b, there was a sufficient amount and sufficient fixation could be achieved. Particularly in this embodiment, since the opening 4 of the metal mask 3 has a shape in which three through-hole lands 2 are connected, a particularly sufficient amount of cream solder 5 can be secured.

Furthermore, since the cream solder 5 is applied to the main body of the discrete component 6 and the land pad 2b, that is, the part where the printed wiring board 1 contacts (see FIG.
d), (e)) It is possible to prevent the cream solder 5 from entering between the discrete component 6 and the land pad 2b, causing the discrete component 6 to be placed or tilted, and causing poor conduction or the like. In addition, since the discrete component 6 can be applied with the cream solder 5 using the metal mask 3 and subjected to the reflow soldering method in the same manner as conventional chip components, it is important to distinguish between the soldering process for the chip component and the discrete component 6. Soldering can be carried out in the same soldering process without any problems. Then, by using the reflow soldering method, when the cream solder melts, the surface tension attracts the discrete component 6 onto the predetermined through-hole land 2, converges on the predetermined position of the printed wiring board, and fixes it in an accurate position. .

[0018]

Effects of the Invention As is clear from the above-mentioned embodiments, the present invention involves passing the cream solder applied to the through-hole land in advance and inserting the lead of the discrete component into the opening of the through-hole land and placing it in a high-temperature electric bath. This allows discrete components to be soldered using the reflow soldering method in the same way as conventional chip components, eliminating the need for separate soldering processes for discrete components and chip components, and reducing the number of soldering processes. This reduces soldering time and cost.

In particular, since the cream solder applied in advance is applied to the outside including the land pad, and except for the part where the main body of the discrete component and the printed wiring board are in contact, a sufficient amount of cream solder can be obtained and the solder can be applied to the outside of the discrete component. The lead of the component and the through-hole land are sufficiently fixed, and cream solder can be prevented from entering between the discrete component and the printed wiring board, causing the discrete component to float or tilt, thereby preventing conduction failure. can be reduced.

[Brief explanation of drawings]

[Figure 1] (a) is a schematic plan view of a printed wiring board (b) is a schematic plan view of a metal mask for cream solder (c) is a schematic plan view after applying cream solder (d) is a schematic plan view of lead insertion for discrete components The later schematic plan view (e) is the side view of (d), and (f) is the schematic plan view after the discrete components are fixed (g).
is a side view of (f)

[Explanation of symbols] 1 Printed wiring board 2 Through hole land 2a Opening 2b Land pad 2c Resist 3 Metal mask 4 Opening 5 Cream solder 6 Discrete parts 7 Lead

Claims (2)

[Claims] Claim 1: A land pad that is a conductive part of a through-hole land formed on a printed wiring board, including the central opening to the outside of the land pad, and excluding the part where the main body of the discrete component and the printed wiring board are in contact. A cream solder application process of applying cream solder, an insertion process of inserting the lead of the discrete component into the opening, and placing the printed wiring board together with the discrete component in a high-temperature electric bath to fix the discrete component to the printed wiring board. A printed wiring board soldering method for discrete components, which comprises a fixing process. 2. A main body of a discrete component including a land pad, which is a conductive part of a through-hole land formed on a printed wiring board, extending to the outside, and having a lead inserted into an opening in the center of the land pad, and the printed circuit board. A metal mask for cream solder that has an opening shaped like the part that contacts the wiring board.