JPH0446671A - Solder reflow method and apparatus thereof - Google Patents

Abstract

PURPOSE:To execute solder reflow having good repeatability by printing cream solder on a substrate, pushing flat-plate type jig for reflow, bringing into close contact, laying to hot plate type heating device and executing the reflow. CONSTITUTION:As the substrate 1 is pushed on the jig 2 having good heat conductivity and both flat surfaces to bring into close contact with these and further, this is heated on the flat hot plate 3, reflow temp. to the substrate 1 can be made to the constant. By this method, the solder reflow having uniform melting condition of the solder in the substrate and good repeatability, can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for strictly controlling the temperature of a substrate, that is, the reflow temperature, when reflowing cream solder printed on a substrate.

[Conventional technology]

In the electronics industry, iron soldering and printed wiring board immersion soldering have long been used as the main soldering methods.

However, in recent years, precision soldering and soldering of minute parts have rapidly developed, and at the same time, high production efficiency for automation and labor saving has been required, and as a result, new soldering technology has been developed to cope with this. , has been put into practical use.

Among these conventional soldering methods, hot plate soldering is a method that uses conduction heat, and convection Methods that use heat include furnace soldering and hot air soldering, methods that use radiant heat include infrared soldering, laser soldering, and light beam soldering, and other special methods include steam condensation. There is a soldering method. Among these methods, the methods that are said to be able to accurately control the temperature are ■ hot air soldering method and ■ steam condensation soldering method. The disadvantage is that the temperature cannot be changed freely, that is, the boiling point of the liquid used cannot be changed. This liquid is a fluorine-based liquid, and Freon is used to prevent the liquid from evaporating and scattering. Freon is also a fluorine-based compound, and in recent years it has become difficult to use it due to environmental issues.

(2) does not have the drawbacks of (2), but in both (2) and (2), the temperature control range is about ±3 to 5°C, making it difficult to use when it is desired to control the temperature with higher precision.

[Problem to be solved by the invention]

When forming a fuse on a board, two conductor circuit terminals separated from each other are formed on the board, and cream solder, that is, solder powder is kneaded with flux and printed in a paste form, spread over both terminals. , this is reflowed to form a fuse. In this case, it is important to note that if the solder is not completely melted, but the surfaces of the solder particles are fused together to form a porous fuse, a fuse that operates stably at a precise temperature can be obtained. The inventors discovered this and filed a separate patent application.

When forming a fuse in this semi-molten state, it is particularly necessary to control the temperature within ±1° C., preferably within ±0.5° C. of the melting temperature of the solder.

Not only in this semi-molten fuse, but also in fuse formation in general, if the temperature rises too high, the IX render will melt, become round, and separate into both terminals, a so-called solder sink. In other words, since the fuse is in an activated state, it is necessary to control the fuse formation temperature within the narrowest possible range.

Furthermore, in general, when mounting components on a board, it is desirable to control the melting temperature of solder within the narrowest possible range in order to prevent damage to the components.

The purpose of the present invention is to print cream solder on a board and, when reflowing it, narrow the temperature variation range around a specified temperature as much as possible, control the temperature with high precision, and also control the temperature holding time with high precision. An object of the present invention is to provide a solder reflow method and an apparatus therefor.

[Means to solve the problem]

The inventors of the present invention conducted extensive research to solve the above-mentioned problem, and as a result, they discovered that the problem could be solved by using a highly thermally conductive flat jig and pressing the substrate against it, and completed the present invention. .

That is, the present invention prints cream solder on a board, presses the board onto a flat jig with good thermal conductivity, and places the jig on a hot plate type heating device. This is a solder reflow method characterized by reflowing the solder.

The device also includes a hot plate type heating means with a temperature control device extending in the longitudinal direction and having a flat top surface, and a moving speed that moves directly above the heating means along the heating means. A solder reflow apparatus for cream solder printed circuit boards, comprising an adjustable endless conveying means and a holding jig placed on the conveying means, the holding jig having good thermal conductivity. This is a /1 reflow apparatus characterized in that a flat plate is provided with a suppressing spring that presses a part of a cream solder printed board onto the flat plate.

When using a hot plate type heating device, the substrate itself is usually placed directly on the hot plate and heated.

However, whether it is a hollow substrate or another substrate, there is generally some co-warpage. When the substrate is warped in this way, a gap is created between the substrate and the hot plate, causing the temperature on the substrate to vary.

In the present invention, a flat jig with a uniform thickness and good thermal conductivity is used, and the board is placed on top of the jig, avoiding the parts of the board where cream solder is printed, parts mounting parts, etc. , the substrate is brought into close contact with the jig by pressing with a pressing means provided on the jig, thereby avoiding variations in the temperature of the substrate.

Therefore, even if the board is warped in either the up or down direction, it is pressed tightly against a jig that has a flat surface with excellent thermal conductivity, so the heat conduction from the jig is good and the heat is not heated. The temperature of the substrate becomes uniform and constant.

Here, both sides of the jig and the surface of the hot plate need to have as good flatness as possible in order to improve heat conduction. In particular, the lower surface of the jig and the surface of the hot plate are important, and it is desirable to have a flatness of 20 μm or less, preferably 10 μm or less for an area of 10100×100.

It is desirable that the top surface of the jig has the same level of flatness, but since this method presses the board from above, if it has a simple curve that will fit tightly when pressed, it can be flattened by about 0.1 mm. good.

The smaller the surface roughness of those surfaces, the better, but it is sufficient to have a JIS fine finish.

The material for the flat plate part of the jig is preferably one with good thermal conductivity, and - for boat fishing, it is better to use metal.

For example, copper, aluminum, and their alloys are preferable. Of course, other materials such as ceramics can also be used as long as they have a certain level of thermal conductivity.

When performing reflow on a large number of substrates within a certain standard temperature range and holding time range, the equipment is equipped with a long hot plate and a jig with the substrates placed on it is moved at a constant speed. If you use a continuous method, you can reflow continuously at high speed.

In this case, it is convenient to use a system in which horizontal bars are provided at regular intervals on an endless driving chain disposed on both sides of the hot plate to push and move a jig such as a sweeper. Of course, the method is not limited to this, and any device may be used as long as it slides the jig over the hot plate at a constant speed.

Covering the top of the hot plate device with heat-resistant glass or the like can prevent the effects of wind and make the temperature more stable.

〔Example〕

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

The invention will be explained with reference to the drawings.

FIG. 1 shows a flat reflow jig 5 used in the method of the present invention placed on a hot plate 3, a substrate 1 on which cream solder is printed on the top surface of the jig 5, and a board 1 on which cream solder is printed. FIG. 4 is a cross-sectional elevational view showing a state in which a substrate is pressed by a substrate pressing spring 4;

Figure 4 shows a copper jig (9) used in the method of the present invention, which has a U-shaped spring made of stainless steel wire on its top surface as a substrate pressing spring.
0x60x4+am) is a perspective view.

2 is a copper flat plate, 4 is a U-shaped stainless wire spring, 7 is a fulcrum, and 6 is a clasp.

5 is a cross-sectional view taken along the line A--A in FIG. 4, and FIG. 6 is a cross-sectional view showing the substrate 1 pressed by a stainless steel spring 4 using 7 as a fulcrum and held down by a clasp 6.

FIG. 2 shows a hot plate 3 in which five hot plates each having a length of 165 mm are arranged in the longitudinal direction and a cooling zone is provided at the end, and a driving chain 8 rotates on both sides of the hot plate 3.
This chain is provided with swirler pars 9 at regular intervals. A board 1 printed with cream solder is placed on a copper flat plate 2, and a stainless steel spring 4 is used to press the board, and a hot plate is heated while controlling the temperature with a PID-controlled temperature control device. The chain 8 was driven, the sweeper 9 was moved to the left, each jig was moved to the left at a constant speed, and the substrate on the jig was heated at a constant temperature for a certain period of time. A cooling zone was provided at the left end.

FIG. 3 is a sectional view taken along the line B--B in FIG. 2.

When we used this jig and reflow equipment to print cream solder on an enamel board and reflow it, we were able to obtain a very stable top surface temperature of the board. When the temperature of the final heating zone (5th zone) is set to 200℃ and the conveyance speed is 381μl/min, the substrate surface temperature is 200±0.
．． We were able to keep the temperature within 5°C.

〔Effect of the invention〕

According to the method of the present invention, the substrate is pressed onto a jig that has good heat conduction and is flat on both sides, and is then heated by placing it on a flat hot plate, so that the temperature of the substrate, that is, the reflow temperature, is kept constant. be able to. Therefore, it is possible to perform solder reflow with good repeatability in which the solder melts uniformly within the board, and high-quality mounting can be performed. Even if the substrate is warped, the temperature can be kept constant.

Furthermore, according to the apparatus of the present invention, the temperature and holding time of the substrate can be automatically controlled with high precision and within an extremely narrow variation range, making it possible to perform solder reflow evenly and with good reproducibility on a large number of substrates. , suitable for mass production.

[Brief explanation of drawings]

Figure 1 shows the method of the present invention in which a flat reflow jig is placed on a hot plate, a board printed with cream solder is placed on the top of the jig, and the board is pressed against the jig by a compression spring to attach it. It is a cross-sectional elevation view showing the state. FIG. 2 is a plan view of the device of the present invention. FIG. 3 is an elevational view of the apparatus of the present invention. FIG. 4 is a perspective view of a reflow jig in which substrate pressing means is provided on the upper surface of a flat plate. FIG. 5 is a side view of a reflow jig consisting of a flat plate and means for pressing the surface thereof. FIG. 6 is a side view showing a state in which a substrate is pressed against the upper surface of a flat plate by a pressing means and attached to a reflow jig. DESCRIPTION OF SYMBOLS 1... Board, 2... Flat plate, 3... Hot plate, 4... Pressing spring, 5... Reflow jig, 6...
... Clasp, 7... Fulcrum, 8... Drive chain, 9... Swivel

Claims (3)

[Claims] (1) Print cream solder on the board, press the board tightly onto a flat reflow jig with good thermal conductivity, and place the jig on a hot plate type heating device. A solder reflow method characterized by reflowing. (2) For the hot plate type heating device,
Claim characterized in that the reflow jig is moved relatively, and other jigs are sequentially placed on a hot plate for reflowing between the time when the jig starts moving and the time when the move ends. 1. The solder reflow method described in 1. (3) A hot plate type heating means with good flatness that can adjust the temperature in the longitudinal direction, and an endless conveying means that moves along the heating means and whose speed can be adjusted. A solder reflow apparatus for cream solder printed boards, comprising a reflow jig placed on the conveying means, wherein the reflow jig is used to transfer cream solder printed boards to a flat plate having good thermal conductivity. 1. A solder reflow apparatus comprising a pressing spring that presses a portion of the flat plate onto the flat plate.