JPH058879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION {Field of Application} The present invention relates to a method of mounting electrical circuit components on a printed circuit board.

{Prior Art} Recently, there has been a growing trend to mount chip components on printed circuit boards due to demands for higher density, automation, and labor saving in component mounting.

Furthermore, the use of discrete components (for example, aluminum electrolytic capacitors) and mechanical parts (for example, switches, jacks, etc.), which have been difficult to make into chips, is rapidly progressing.

These parts generally have poor heat resistance, so it is difficult to solder them directly with a solder dip, and many of them are compatible with reflow soldering.
It began to be reflow soldered to printed circuit boards along with other chip components.

In particular, among such parts, chip-type aluminum electrolytic capacitors (hereinafter referred to as aluminum chips) have the following drawbacks when reflow soldered.

Aluminum chips have a larger volume than other chip components, and are often used as external components for semiconductor ICs. In this case, if they are placed in isolation, the circuit characteristics may become unstable due to the increase in L and R components. Because of the reason why it is necessary to use them in close proximity,
The heat capacity becomes large in some parts of the printed circuit board due to the dense soldering, and as a result, it is difficult for the temperature of the closely arranged (dense parts) parts to rise during reflow, and the solder does not melt uniformly during melting, resulting in so-called melting variations. Poor bonding occurred.

Furthermore, if the reflow temperature is raised until the solder in the closely spaced parts is sufficiently melted and bonded, the temperature of the part with low heat capacity, that is, the isolated aluminum chip, will rise too much, and the aluminum chip will have to use electrolyte. As a result, the internal pressure of the element increases, causing problems such as electrolyte leakage and, in extreme cases, deterioration of the characteristics of the element, such as destruction of the element.

{Object of the invention} The object of the present invention is to eliminate the above-mentioned drawbacks and to perform highly reliable soldering, especially when mounting heat-sensitive parts such as aluminum chips on a printed circuit board. .

{Summary of the Invention} The present invention provides a soldering method in which, when reflow soldering components to a printed circuit board, a solder having a lower melting point than other parts is used in parts where the heat capacity increases due to close placement etc. It's a method.

{Embodiments of the Invention} Below, examples of the present invention will be described using aluminum chips as an example.
This will be explained with reference to the drawings. It can also be applied to other parts.

FIG. 1 shows a mounting process according to the present invention.

First, as shown in Fig. 1a, paste solder 5 is applied by screen printing to the rounds 2 and 4 for mounting parts other than the round in the vicinity of the aluminum chip of the printed circuit board 1 (Fig. 1b). Paste solder 6 having a lower melting point than solder 5 is applied to 3 using a dispenser. (Fig. 1c) Normally, eutectic solder is used for reflow soldering, but when using eutectic solder for solder 5, paste solder 6 should have a low melting point of 20 to 50°C. It is desirable to use

Next, as shown in FIG. 1d, after mounting the aluminum chips 7, 8 and chip parts 9, they are heated in a heating atmosphere furnace.
Melt the paste solder and complete the bonding. (Fig. 1 e) According to this method, due to the characteristics of the circuit, multiple pieces are placed close together, and low melting point solder is used in areas where the heat capacity increases and the temperature is difficult to rise, so it is impossible to forcibly bond the entire printed circuit board. There is no need to raise the temperature of the parts, and there is no deterioration of component characteristics in isolated parts.

{Effects of the Invention} According to the present invention, it is possible to perform reflow soldering of parts in densely arranged parts without deteriorating the characteristics of the isolated parts (for example, aluminum chips).

[Brief explanation of the drawing]

FIG. 1 is a process diagram for explaining implementation of an embodiment of the present invention. Explanation of symbols, 1...Printed circuit board, 2...Round for aluminum chips placed in isolation, 3...Round for aluminum chips placed close together, 4...Round for chip parts, 5...Solder, 6...Low melting point solder,
7, 8... Chip type aluminum electrolytic capacitor (aluminum chip), 9... Chip parts.

Claims (1)

[Claims] 1. Solder with a lower melting point than other rounds is used for rounds in areas where the temperature is difficult to rise due to crowded parts, etc., and melting on the board when parts are mounted on the printed circuit board by reflow soldering is used. A mounting method characterized by soldering while correcting variations. 2. The mounting method according to claim 1, wherein the component is a chip-type aluminum electrolytic capacitor.