JPS63133696A - Vapor phase reflow soldering - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Soldering by vapor reflow is a method in which cream solder is applied to a printed wiring board, electronic components are mounted, and then heating is performed in the order of a preheating step, a main heating step, and a cooling step. By cooling, it is possible to solder without applying thermal stress due to thermal shock to the solder joints of mounted components and printed wiring boards.

[Industrial application field]

The present invention relates to improvements in vapor reflow soldering methods for reflow soldering surface mount components.

There is a well-known vapor reflow soldering method in which cream solder is applied to a printed wiring board, surface mount components are mounted, and the cream solder is melted and bonded by heating reflow. If the liquid is heated and vaporized and suddenly exposed to an atmosphere maintained at the solder melting temperature, it will cause thermal stress due to thermal shock to mounted components, printed wiring boards, solder joints, etc., causing cracks in the components and accumulation of thermal stress. Therefore, there is a demand for a vapor reflow method for soldering without applying heat stress.

[Conventional technology]

Conventionally, as shown in the side sectional views of FIGS. 3 and 4, in the badge type shown in FIG. 3, when the Freon liquid 12a placed in the Freon liquid tank 10 is heated by the heater 12b,
Freon liquid 12a is vaporized to a liquid-specific temperature of approximately 220°C.
When a Freon gas atmosphere 12c of .degree. C. is created and cooled by an upper cooling coil 12d, the vaporized Freon gas condenses and becomes a Freon liquid 12a again, falling downward. This reaction can be repeated to maintain the atmosphere 12c at the above temperature.

Apply cream solder (as shown) and attach the surface mount component 15a.
The printed wiring board 15 equipped with is inserted into this atmosphere 12c, the cream solder is heated and melted, and then taken out.
Soldering is a joining method in which the solder is fixed by cooling to room temperature.

In addition, in the side sectional view of the tunnel type shown in Fig. 4,
This is a method that allows continuous soldering for the badge type, and the Freon liquid 12a'' placed in the Freon liquid tank 10'' is heated with a heater 12b'' in the same way as the badge type, and the Freon liquid 12a'' is vaporized. A Freon gas atmosphere 12c' with a liquid-specific temperature of about 220°C is created, and this is cooled and condensed in the upper cooling coil 12d' in the same way as in the badge type above to form a Freon liquid 12a°, and this reaction is repeated. The atmosphere at the above temperature was maintained at 12c.

Belt conveyor 14 on both sides of Freon liquid tank 10゛
A passage port 12f' is provided, and a cooling corrugated pipe 12e is disposed on the inner periphery of the passage port 12f'' to re-liquefy the Freon gas and prevent it from flowing out.

Apply cream solder (as shown) and attach the surface mount component 15a.
Printed wiring boards 15" loaded with "15" at room temperature are placed one after another on this belt conveyor 14" and passed through the above atmosphere 12". During the passage, cream solder is heated and melted and cooled to room temperature outside the tank 10". Soldering is a joining method in which the solder is fixed by doing this.

[Problem that the invention seeks to solve]

However, according to the above-mentioned method, the printed wiring board on which the mounted components are mounted is suddenly inserted from room temperature into an atmosphere maintained at the melting temperature of the solder, resulting in a large temperature difference. There is a problem in that the thermal stress caused by thermal shock is applied to the solder joints, which may cause cracks in the component or cause the thermal stress to accumulate.

The present invention provides a vapor reflow soldering method that solves the above problems.

[Means for solving problems]

The above problem with the conventional method is that after applying cream solder to a printed wiring board and mounting electronic components, there is a preheating step A in which the board is gradually preheated, a main heating step B in which the solder is melted, and a slow cooling step. This problem can be solved by heating and cooling the solder joint in the order of cooling step C.

[Effect]

The solder joint is gradually heated from room temperature in the preheating step A, the cream solder is melted in the main heating step B, and gradually cooled to room temperature in the cooling step C, which reduces the temperature difference and prevents thermal shock. Soldering is possible without applying any force.

〔Example〕

The gist of the present invention will be explained in detail below based on embodiments shown in the drawings.

As shown in the side sectional view of the tunnel type atmosphere tank in Figure 1,
A heater 2b for heating and vaporizing the Freon liquid 2a is provided at the bottom of the main heating tank 2 containing the Freon liquid 2a, and a cooling pipe 2d for re-liquefying the vaporized Freon gas atmosphere 2c is provided at the top of the vaporized Freon gas atmosphere 2c. A passage port 2f of the belt conveyor 4 is opened, and a cooling corrugated pipe 2e is placed around the inner periphery of the passage port 2f to re-liquefy the Freon gas and prevent it from flowing out.

Adjacent to the main heating tank 2 and on the inlet side, the furnace chamber 1a is partitioned 1c.
A preheating furnace 1 is provided with heaters 1b disposed above and below which are distributed and temperature controlled so as to gradually raise the temperature and preheat. A cooling furnace 3 is installed in which heaters 3b whose temperature is controlled and distributed to provide cooling are arranged above and below, and a belt conveyor 4 is run from an inlet 1d to an outlet 3d.

The preheating furnace 1 controls the temperature of the heater 1b to maintain the temperature from about 50°C on the inlet side to a final temperature of about 150°C for the preheating process, and the main heating tank 2 is heated to about 220°C by the heat of vaporization of the Freon liquid 2a. The main heating step B is performed to melt the solder, and the temperature of the cooling furnace 3 is controlled to about 15
Cooling process C is performed while maintaining the outlet side at about 40°C from 0°C.

That is, when a room-temperature printed wiring board 5 coated with cream solder (the path shown) and mounted with surface mount components 5a is placed on the belt conveyor 4 and passed from the inlet 1d to the outlet 3d, -
As an example, as shown in the temperature curve shown in Figure 2, the temperature is first gradually raised from room temperature in the preheating furnace 1 to about 140°C, and then it enters the main heating tank 2 and soldered at about 210°C. is melted, then enters the cooling furnace 3, where it is gradually cooled to solidify the solder, and the temperature is lowered to about 50° C., and then taken out of the furnace and cooled to room temperature.

According to the above method, the preheating furnace 1 and the cooling furnace 3 provided before and after the main heating tank 2 gradually heat and cool the main heating tank 2, so that the temperature difference between them is kept small and the thermal stress caused by thermal shock is reduced. can be reduced to a small extent.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to perform soldering without cracking components or causing thermal stress, and this invention exhibits an extremely useful effect of improving the reliability of mounted components, printed wiring boards, and solder joints. do.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of an embodiment according to the present invention, Fig. 2 is a temperature curve diagram of this embodiment, Fig. 3 is a side sectional view of a badge type according to the prior art, and Fig. 4 is a side sectional view of a conventional badge type. FIG. In the figure, 1 is a preheating furnace, 1a is a furnace chamber, 1b is a heater, 1c is a partition, 1d is an inlet, 2 is a main heating tank, 2a is a Freon liquid, 2b is a heater, and 2c is an atmosphere. 2d and 2e are cooling corrugated pipes, 2f is a passage port, 3 is a cooling furnace, 3a is a furnace chamber, 3b is a heater, 3c is a partition, 3d is an outlet, 4 is a belt conveyor, 5 is a printed wiring board, 5a is a mounted component , indicates. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] After applying cream solder to a printed wiring board and mounting electronic components, there is a preheating step A in which the electronic components are gradually preheated, a main heating step B in which the solder is melted, and a cooling step C in which the solder is slowly cooled.
A vapor reflow soldering method characterized by heating and cooling a solder joint in the following order.