JPH0191494A - Method of soldering component to printed board - Google Patents

Abstract

PURPOSE:To eliminate soldering defects, by applying low-melting solder cream and high-melting solder cream in two layers on a pad and soldering a lead to the pad while melting the two solder layers. CONSTITUTION:Low-melting solder cream 13 and high-melting solder cream 14 are applied in two layers on a lead connecting pad 12, and the two solder layers are heated with a lead 16 disposed on the pad 12. Thereby, the low- melting solder cream 13 is diffused quickly over the lead connecting pad 12 so that a molten solder layer is formed on the pad 12 without any solder absorbed up by the lead 16. Further, the high-melting solder cream 14 is not molten enough when the low melting solder cream 13 is fusion bonded to the lead 16. In this manner, the leaded 16 can be secured positively to the soldering pad 12 while preventing almost all of the solder from being absorbed up to the lead 16. Thus, soldering defects can be eliminated.

Description

[Detailed Description of the Invention] [Summary] Soldering of electronic components on a printed circuit board relates to a method that ensures that the lead wires are securely connected when soldering the lead wires of electronic components to the lead wire connection pads of the printed circuit board. In a method for connecting a lead wire connection pad provided on the surface of a printed circuit board and a lead wire led out from an end of an electronic component, the lead wire is soldered to a connection pad on the pad. It is constructed by applying a low melting point solder cream and a high melting point solder cream in a two-layer structure, and soldering the lead wire to the lead wire connection pad while melting the solder layer of the two-layer structure.

[Industrial application field]

The present invention relates to a method for soldering a printed circuit board having a surface mount structure, and particularly to a method for soldering a lead wire for connecting an electronic component to a soldering pad provided on a printed circuit board.

A printed circuit board with a surface mount structure, in which an electronic circuit is molded in resin and lead wires derived from the resin-molded electronic components are connected by soldering to lead wire connection pads provided on the printed circuit board, It has recently been used as a printed circuit board capable of high-density mounting because it does not require through holes to connect conductor layer patterns, and electronic components can be mounted on both the front and back sides of the printed circuit board.

[Conventional technology]

To explain the conventional soldering method for a printed circuit board with such a surface mount structure, as shown in FIG. The solder cream 3 is applied using a screen printing method. Further, a lead wire 5 led out from a molded body 4 in which an electronic circuit is molded with resin is installed on the lead wire connection pad 2, and the lead wire 5 is connected by heating and melting this solder using infrared rays or heated nitrogen gas. It is connected to the lead wire connection pad 2.

Surface mounting technology (Surface mounting technology) is a technology for mounting electronic components without providing through holes on the surface of the printed circuit board 1.
It is suitable for high-density mounting because there is no need to provide through holes on the printed circuit board.

[Problems to be Solved by the Invention] However, in such a method, as shown in FIG. 3(a), the material of the lead wire 5 generally has a higher wettability to solder than the material of the connection pad 2. In many cases, therefore,
A phenomenon occurs in which the molten solder cream 3 is sucked up to the lead wire 5, and as shown in FIG. 3(b), there is no solder on the connection pad 2, so that the lead wire 5 and the connection pad 2 are sufficiently fixed. The problem arises if you don't.

The present invention solves the above-mentioned problems, and when connecting the lead wire and the lead wire connection pad, the solder of the connection pad is sucked up by the lead wire, resulting in a shortage of solder on the connection pad, and the lead wire The object of the present invention is to provide a method for preventing the connection pad from becoming insufficiently bonded to the connecting pad.

[Means for solving problems]

The method of the present invention for solving the above problems is a method for connecting a lead wire connection pad provided on the surface of a printed circuit board and a lead wire led out from an end of an electronic component.
It is constructed by applying a low melting point solder cream and a high melting point solder cream on the pad in a two-layer structure, and soldering the lead wire to the lead wire connection pad while melting the solder layer of the two-layer structure. .

[For production]

In the method of the present invention, a low melting point solder cream and a high melting point solder cream are applied to a lead wire connection pad in a two-layer structure, a lead wire is placed on the pad, and the two-layer structure of solder is heated. The lower layer low melting point solder cream quickly adapts to the lead wire connection pad and spreads, so that a molten solder layer is formed on the pad without the solder being sucked up to the lead wire side. Further, when the low melting point solder cream is melted on the lead wire, the upper layer high melting point solder cream is not sufficiently melted. Further, unlike in the conventional method, most of the solder on the pad is prevented from being sucked up to the lead wire side, and the lead wire and solder are sufficiently bonded to the pad.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1(a), flux is mixed onto the lead wire connection pad 12 of the printed circuit board 11.
A low melting point solder cream 13 (manufactured by Senju Metal Co., Ltd., trade name: 1t165) having a melting point of 130 to 160° C. is applied by screen printing.

Next, as shown in FIG. 1(b), a high melting point solder cream 14 having a melting point of 180° C., which is mixed with flux, is applied onto the low melting point solder cream 13 by screen printing.

Next, as shown in FIG. 1(C), the lead wire 16 led out from the end of the molded body 15 in which the electronic circuit is molded with resin is placed on the lead wire connection pad 12, and the two-layer structure is soldered. The cream layers 13 and 14 are melted using infrared rays or heated nitrogen gas, and the lead wires 16 are soldered and fixed onto the pads 12.

Then, in soldering, since the low melting point solder cream layer 13 is formed on the first layer on the pad 12, when the two layered solder cream layer 13.14 is heated, the first layer low melting point solder cream N13 is heated. However, it quickly melts and spreads on the pad 12 without being sucked up by the lead wire 16.

Furthermore, since the high melting point solder cream 14 is not sufficiently melted when the low melting point solder cream is melted, it is possible to prevent most of the melted solder from being sucked up to the lead wires 16 as in the conventional case. As shown in d), the lead wire connection pad 12 and the lead wire 16 are sufficiently bonded to each other by the melted two-layer solder cream 13 and 14.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to prevent the phenomenon in which the molten solder on the pad is sucked up to the lead wire during soldering.
6 is sufficiently fixed, and a highly reliable printed circuit board with no soldering defects can be obtained.

[Brief explanation of the drawing]

1(a) to 1(d) are cross-sectional views showing the method of the present invention in the order of steps, FIG. 2 is an explanatory diagram of the conventional method, and FIG. 3(a) and FIG. It is an explanatory view showing an inconvenient state. In the figure, 11 is a printed circuit board, 12 is a lead wire connection pad, 1
3 is a low melting point solder cream, 14 is a high melting point solder cream,
15 is a molded body, and 16 is a lead wire. (Q) Unexploded gAp, γ3 ゑ T 100 buttons; Explanatory diagram Figure 3

Claims (1)

[Claims] In a method for connecting a lead wire connection pad (12) provided on the surface of a printed circuit board (11) and a lead wire (16) led out from an end of an electronic component, the pad ( 12) Low melting point solder cream on top (13)
and high melting point solder cream (14) in this order to form a two-layer structure, and while melting the solder layer of the two-layer structure, the lead wire (16) is soldered to the lead wire connection pad (12). A method for soldering components to a printed circuit board, characterized by: