JPH0444391A - Reflow soldering - Google Patents

Abstract

PURPOSE:To make uniform the heating temperature of the whole printed board by a method wherein an electronic component is placed on the land of the board via a solder, this component is brought into contact to a liquid heated to a desired temperature to be subjected to heating, the solder is made to melt and the component is jointed to the land. CONSTITUTION:A printed board B is put in a state that a cream solder 5 is fed to a solder land 3 provided on a substrate 2 and an electronic component 4 is placed and is prepared for a soldering and is heated to 220 deg.C with a high- temperature liquid A. Accordingly, when the lower surface of the board B is brought into contact to the liquid A, the solder 5 is heated and melted by a heat conduction of the substrate 2 and leads of the component 4 are jointed to the land 3. As the solder 5 is made to melt via the heat conduction of the substrate 2 in such a way, an abrupt thermal shock is not applied to the component 4. As a result, its effect is hardly inflicted on the component 4. Moreover, even in the case there is a warpage in the substrate 2, the liquid A comes into closely contact to the substrate 2 because the heating unit is a liquid and the soldering is executed without generating an unevenness in heating according to a position.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a reflow soldering method used for surface mounting electronic components and the like.

Conventional technology As a heating method for reflow soldering, various methods have been used to heat the entire printed circuit board at once, and each method has its advantages and disadvantages, but the following three methods are the main ones: It is used.

(1) To solder a board, place cream solder on the land, place the electronic component on it, heat it with a heater from above, and use the radiant heat to melt the cream solder and join the electronic component to the land.

(2) A VPS (vapor face solder link) method in which a printed circuit board prepared for reflow soldering is placed in high-temperature steam and the cream solder is melted and bonded by the heating of the high-temperature steam.

(3) Place the printed circuit board prepared for reflow soldering on the hot plate and heat the board from the bottom.
A method of joining by melting cream solder using heat conduction on the board.

Problems to be Solved by the Invention With reflow soldering, the parts to be connected are not immersed in molten solder, so there is less thermal shock to the parts, and only the necessary parts can be soldered, eliminating the possibility of soldering problems such as bridges. It has the advantage of having less However, the quality of reflow soldering depends on the heating method, so selection of the heating method is important.

In the first conventional example above, variations in heating temperature tend to occur between electronic components with different heat capacities, so it is necessary to increase the heating temperature or increase the heating time. Parts may deteriorate at high temperatures.

In addition, in the second conventional example, the latent heat of the high-temperature steam is large and the solder is rapidly heated. Therefore, if the melting timing of the solder is off, one side of the bonded parts may develop chips, etc. Attachment is likely to cause defects. Furthermore, in order to stabilize the heating conditions, it is necessary to seal the high-temperature steam or to continuously supply high-temperature steam, which results in a problem that the apparatus becomes complicated and the amount of steam consumed increases.

Furthermore, in the third conventional example, since it is affected by the thermal conductivity of the substrate, if the substrate is warped, there will be no gap between the substrate and the hot plate, so the substrate surface cannot be heated uniformly. This becomes difficult.

It is an object of the present invention to provide a reflow soldering method that solves the above-mentioned conventional problems.

Means for Solving the Problems In order to achieve the above object, the present invention places an electronic component on a land of a printed circuit board via solder, and heats it by bringing it into contact with a liquid heated to a predetermined temperature. By this,
Reflow soldering is a method characterized in that the electronic component is bonded to the land by melting the solder.

Further, the second invention of the present application is such that the lower surface of the printed circuit board is brought into contact with the surface of the high-temperature liquid, and the other surface is exposed to the space above the high-temperature liquid, and the solder is melted by heating the printed A board from the lower surface side. Reflow soldering is a method characterized by:

Furthermore, a third invention of the present application is a reflow soldering method characterized by melting the solder by immersing the entire printed circuit board in a high-temperature liquid.

According to the present invention, although the latent heat of liquid is relatively large, it is small compared to gas, so even if adjacent electronic components have different heat capacities, it is possible to equalize the heating temperature of the entire printed circuit board. Since the solder can be melted gently, defects can be reduced when soldering with chips or the like.

Further, according to the second invention of the present application, the lower surface of the printed circuit board can be brought into close contact with the high temperature liquid, so the printed circuit board can be heated uniformly. Also, since the solder is heated from below the printed circuit board, the solder can be heated from below. Even if heat-sensitive electronic components are mounted on the top surface of a printed circuit board, they will not receive direct thermal shock and can avoid high-temperature deterioration.This is a printed circuit board with double-sided mounting. In some cases, even electronic components that tend to fall off the bottom of the printed circuit board are affected by the buoyancy of the high-temperature liquid, making it difficult for them to fall off the printed circuit board.

Further, according to the third invention of the present application, heating is performed from both sides of the printed circuit board simultaneously, thereby reducing the working time required for soldering.

Embodiment FIG. 1 shows an embodiment of the present invention, in which the lower surface of the printed circuit board B is brought into contact with the surface of a high-temperature liquid heated to a high temperature, and the cream solder supplied to the required locations on the printed circuit board B is melted. This is a method for connecting electronic components to printed circuit board B.

The high-temperature liquid A is temperature-controlled by heating Noricone oil, high-boiling-point cutting, etc., to efficiently melt the cream solder, and is set at a temperature that does not cause any damage to the circuit boards or mounted components that make up the printed circuit board. Ru. In this example, the melting point of the cream solder is 183°C, so the high temperature liquid A is
Reflow soldering using liquid heated to 20°C has achieved results suitable for the process.

As shown in FIG. 1, the printed circuit board B has cream solder 5 supplied to the soldering land 3 provided on the board 2, and the soldering land 3 on which the electronic component 4 is placed is in a ready state, and the soldering land 3 provided on the board 2 is in a ready state, and
is heated to 220°C, so when the bottom surface of the printed circuit board B is brought into contact with the heating liquid 1, the cream solder 5 is heated and melted by the heat conduction of the circuit board 2, joining the leads and lands 3 of the electronic component 4. do.

According to the above method, since the cream solder 5 is melted through thermal conduction of the board 2, a sudden thermal shock is not applied to the electronic components 4. It has little effect on parts. Furthermore, even if the substrate 2 is warped, since the heating element is a liquid, the high-temperature liquid A and the substrate 2 come into contact without any gaps, and soldering can be performed without uneven heating depending on the position.

FIG. 2 shows a method of soldering by immersing a printed circuit board B, which has been prepared for reflow soldering, into a high-temperature liquid A. According to this method, the printed circuit board B is heated uniformly regardless of its size, and the heating efficiency is extremely high. Therefore, the time required for the solder to melt is short, so the working time required for soldering can be shortened. .

This method is effective when simultaneously soldering both sides of a double-sided mounting board with electronic components 4 mounted on both sides of the board 2 in order to increase the mounting density of the printed circuit board.
If electronic components that are susceptible to high-temperature deterioration are used, they will be directly affected by the high-temperature liquid A. In such a case, as shown in Fig. 3, the printed circuit board 2 is placed so as to float on the surface of the high-temperature liquid A, and one side of the printed circuit board B is submerged in the high-temperature liquid A, and the other side is exposed to the upper space. Heating methods can be used.

In this way, if only the bottom surface is immersed in high-temperature liquid A with the side on which electronic components that are prone to high-temperature deterioration are placed facing up, the bottom surface will be soldered by direct heating by high-temperature liquid A, and the top surface will be soldered. Soldering is performed by gentle heating through the substrate 2. Therefore, if the side on which electronic components that are prone to high-temperature deterioration are mounted is placed on the top surface, direct thermal shock can be avoided.

The solder supply method in reflow soldering described above has been described as a method using cream solder, but it goes without saying that similar effects can be obtained by methods such as solder precoating.

Effects of the Invention According to the present invention, although the latent heat of liquid is relatively large, it is small compared to gas, so even if adjacent electronic components on the printed circuit board have different heat capacities, the heating temperature of the entire printed circuit board can be made uniform. In addition, since the solder can be melted gently, it is possible to reduce soldering defects such as chipping.

Further, according to the second invention of the present application, one surface of the printed circuit board can be brought into close contact with the high temperature liquid without any gaps, so that the printed circuit board can be heated uniformly. Also, since the solder can be heated from below the printed circuit board, heat-sensitive electronic components can be placed on the other side of the printed circuit board! ! High temperature deterioration can also be avoided even if the If the board is double-sided mounted, electronic components that are easily dropped from the bottom of the printed circuit board can be prevented from falling from the printed circuit board by receiving the buoyancy of the high-temperature liquid.

Furthermore, according to the third aspect of the present invention, the work time required for soldering is shortened by heating the entire printed circuit board from both sides.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment method of the present invention, Fig. 2 is an explanatory diagram of a method of immersing it in a high-temperature liquid, and Fig. 3 is an explanatory diagram of a method of placing a double-sided mounting board on the surface of a high-temperature liquid. be. High temperature liquid printed circuit board/board land/electronic component cream solder

Claims (3)

[Claims] (1) An electronic component is placed on a land of a printed circuit board via solder, and the solder is melted by heating the electronic component by contacting it with a liquid heated to a predetermined temperature and bonding the electronic component to the land. A reflow soldering method characterized by: (2) The lower surface of the printed circuit board is brought into contact with the surface of the high-temperature liquid, and the upper surface thereof is exposed to the space above the high-temperature liquid, and the solder is melted by heating the printed circuit board from the lower surface side. The reflow soldering method according to claim 1. (3) Claim 1, characterized in that the solder is melted by immersing the entire printed circuit board in a high-temperature liquid.
Reflow soldering method as described.