JPH0399493A - Reflow soldering method - 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] Regarding the improvement of the reflow soldering method for surface-mounted printed circuit board units, the present invention aims to equalize the dispersion in soldering temperature between components with different heat capacities by printing on printed circuit boards. In the reflow soldering method, in which components are mounted on paste-like solder and heated to melt the solder, the printed board on which the components are mounted is cooled in advance by a cooling mechanism before reflow heating. Subsequently, reflow heating is performed to equalize variations in soldering temperature that occur between components having different heat capacities.

[Industrial application field]

The present invention relates to an improvement in a reflow soldering method for surface-mounted printed circuit board units.

[Conventional technology]

In the reflow soldering method, solder paste is printed on the component mounting area of a printed board, the components are placed on top of it, and the solder is heated to melt the solder.Heating is done using infrared heating or solvent vapor. Heating is used.

FIG. 3 is a diagram showing a conventional reflow soldering apparatus using infrared heating. In the figure, 1°1' is a heater, 2 is a conveyor, and 3 is an operation panel.While conveying a printed board 4 on which parts are placed on solder paste in the direction of arrow A by the conveyor 2, the heater 1. 1', the solder can be melted and soldered.

[Problem to be solved by the invention]

In the reflow soldering method using the conventional reflow soldering apparatus described above, as shown in FIG. 4, a temperature difference occurs during heating between components mounted on the same printed board and having different heat capacities. In this figure, the vertical axis shows component temperature and the horizontal axis shows elapsed time. Curve A shows the temperature profile of the printed board, curve B shows the temperature profile of an SOP type 8-pin semiconductor device, and curve C shows the temperature profile of a QFP type 120-pin semiconductor device. The temperature profile of each semiconductor device is shown in FIG. Also, the portion D where each curve is slightly horizontal is a preheating portion. The figure shows that there is a temperature difference of about 40° C. during reflow heating between an SOP type 8-bin semiconductor device with a small heat capacity and a QFP type 120-pin semiconductor device with a large heat capacity.

Due to such causes, components with small heat capacity such as SOP type 8-bin semiconductor devices and transistors may experience excessive temperature rise and thermal breakdown.

As a countermeasure to this problem, there is a method of covering parts with small heat capacity with a heat-resistant mask made of a metal plate such as AjCu and soldering them, but this method has the problem that the work becomes extremely complicated.

SUMMARY OF THE INVENTION In view of the above conventional problems, an object of the present invention is to provide a reflow soldering method that evens out variations in soldering temperature between components having different heat capacities.

[Means to solve the problem]

In order to achieve the above object, in the reflow soldering method of the present invention, components are mounted on paste-like solder printed on a printed board, and the solder is heated to melt the solder. , the printed board 4 on which the above components are mounted is cooled in advance by the cooling mechanism 5 before reflow heating, and then reflow heating is performed to equalize the dispersion in soldering temperature that occurs between components with different heat capacities. shall be.

[For production]

Generally, parts with small heat capacity heat up and cool down easily.

Conversely, parts with a large heat capacity are difficult to heat and cool. Taking advantage of this property, the printed circuit board with components mounted on it is cooled by a cooling mechanism to make components with smaller heat capacity lower than those with larger heat capacity, thereby increasing the temperature difference from the next preheating temperature. As a result, even if the temperature rises quickly during preheating, the temperature will be almost the same as that of a component that has a large heat capacity and whose temperature rises slowly, and it is possible to reduce temperature variations during the next reflow.

〔Example〕

FIG. 1 is a diagram showing a reflow soldering apparatus capable of implementing the method of the present invention.

This device includes a heater 1.1', a heater 1.1',
This device is similar to the conventional example explained in FIG. 3 in that it has a conveyor 2 for conveying a printed board 4 with components mounted inside it, and an operation panel 3.The feature of this device is that it has a cooling mechanism at the entrance of the device. 5 and a conveyor 6 were provided. This cooling mechanism includes a refrigerant pipe 7, a fan 8, and the like. Further, the conveyor 6 is separated from the conveyor 2 for the reflow oven in order to prevent heating by the reflow oven.

Next, a method of the present invention using the apparatus configured as described above will be explained.

First, components are mounted on a printed board 4 on which paste-like solder has been printed and applied to the component mounting portion in advance, and the components are placed on a conveyor 6 in the six directions of arrows and fed into the cooling mechanism 5. In this case, parts with small heat capacity are cooled to below room temperature. For example, in the case of an 8-bottle SOP type semiconductor device, when the preheating temperature is set to 150° C., the device is cooled to a temperature approximately 30° C. lower than room temperature. This cooled printed circuit board 4 is then conveyed by the conveyor 2 into the heater 1.1' and preheated (e.g.
(about 50℃), then reflow heating (for example, about 240℃)
be done.

Figure 2 is a diagram showing the temperature profile in the above case, with elapsed time on the horizontal axis and temperature on the vertical axis, where curve A is the printed board, curve B is the SoP type 8-pin semiconductor device, and curve C is the Q
The temperature profile of an FP type 120-pin semiconductor device is shown. Printed board and SoP as shown in the figure
The 8-pin type semiconductor device has a small heat capacity, so it cools down faster and reaches a lower temperature than the 120-pin QFP type semiconductor device, which has a large heat capacity, but the temperature rises faster during preheating, so
At the end of preheating (indicated by arrow P), all are at approximately the same temperature. This also reduces variations in temperature during reflow heating.

〔Effect of the invention〕

As explained above, according to the present invention, by cooling the printed circuit board on which components are mounted before preheating for reflow soldering, temperature variations among the components at the end of preheating can be reduced, and This makes it possible to reduce temperature variations during reflow heating performed by heating.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a reflow soldering device capable of implementing the method of the present invention, FIG. 2 is a diagram showing a temperature profile obtained by the present invention, and FIG. 3 is a diagram showing a conventional reflow soldering device. FIG. 4 is a diagram showing a temperature profile obtained by a conventional reflow soldering method. In the figure, 1.1' is a heater, 2.6 is a conveyor, 3 is an operation panel, 4 is a printed board, 5 is a cooling mechanism, 7 is a refrigerant pipe, and 8 is a fan. Figure 8: A book showing the temperature feeling obtained by the fan according to the present invention Figure C: A diagram showing a conventional reflow soldering device for a QFP type 120-bin semiconductor device Time (seconds) Conventional reflow soldering Diagram showing the temperature profile obtained by the attachment method

Claims (1)

[Claims] 1. In the reflow soldering method, in which components are mounted on paste-like solder printed on a printed board and heated to melt the solder, before reflow heating the printed board (4) on which the above components are mounted. , A reflow soldering method characterized in that variations in soldering temperature that occur between components with different heat capacities are made uniform by cooling in advance with a cooling mechanism (5) and then performing reflow heating.