JPH05136555A - Method of soldering printed wiring board - Google Patents

Abstract

PURPOSE:To prevent a printed wiring board from being transformed or deteriorated by heat and to prevent pads from being separated by a method wherein the printed wiring board is placed on a table made of a resin having a specified heat conductivity and a reflow soldering is conducted. CONSTITUTION:Cream solders 14 and 14 are respectively fed on pads 12 and 12 on a printed wiring board 10. A surface mount component 16 is fixed over this board 10. Thus board 10 is placed on a table 20. This table 20 is one made of a resin having a heat conductivity in a range of 6X10<-4> to 18X10<-4>Cal/ cm.sec. deg.C. After that, a current is made to flow through heater chips 22 in a state that leads 18 are pressed by the chips 22 from above. At this time, as the board 10 is placed on the table 20 having a proper heat conductivity and heat of the board 10 is rapidly diffused in the table 20, soldering parts are heated to a proper temperature, the cream solder 14 is molten and the leads 18 are normally soldered to the pads 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering method for a printed wiring board, in which a surface mount type component is reflow-soldered on the upper surface of the printed wiring board by an instantaneous heating method.

[0002]

2. Description of the Related Art As a method for soldering a surface mount type component to a printed wiring board, a reflow soldering method using a reflow furnace has been conventionally known. This reflow soldering method uses solder plating or cream solder to supply solder to the soldering points (hereinafter referred to as "pads") on the printed wiring board in advance, and then fix the parts to the electric furnace or infrared furnace (these are It is called a reflow oven) and is heated to melt the solder.

When solder is supplied here by solder plating, the parts are fixed by an adhesive, and when cream solder is used, the parts are fixed by the viscosity of the cream solder itself. In the reflow furnace used here, usually 1
After preheating at 20 to 150 ° C. for 30 to 60 seconds, this is followed by main heating at 210 to 230 ° C. for about 30 seconds. As described above, the method using the reflow furnace has a problem that it cannot be applied to soldering of components having poor heat resistance because both the printed wiring board and the mounted components are exposed to high temperatures.

Therefore, when the reflow soldering method is applied to such a part having poor heat resistance, an instantaneous heating method has been conventionally used in which a heater chip is pressed against only the soldering part of the part to heat it. With this method, a heater chip made of high-resistance metal such as molybdenum (MO) or tungsten (W) that does not get wet with solder is heated by instantaneously passing an electric current, and this heat is transmitted to the soldering section to melt the solder. To do.

In this instantaneous heating method, a printed wiring board is usually placed on a table of phenol resin having excellent heat resistance for soldering. That is, the heater chip heats while sandwiching the soldering part of the component, the pad of the printed wiring board, and the base material of the printed wiring board between the table and the table. The table used here had very low thermal conductivity and poor heat dissipation.

The heating temperature is detected by a thermocouple mounted near the tip of the heater chip. This heating is 3
It is divided into primary heating (preheating) that is heated at 00 ° C. for 9 seconds and secondary heating (main heating) that is subsequently heated at 450 ° C. for 5 seconds. In this way, the heater chip itself is 45
Even if the temperature becomes higher than 0 ° C, the time is sufficiently short so that the parts are not damaged.

However, when the printed wiring board is thin, for example, about 0.2 mm, the heat of the heater chip quickly raises the temperature of the printed wiring board itself. Generally, a printed wiring board using a typical polyimide resin as a heat resistant resin has a guaranteed range of a heat resistant temperature of 288 ° C. and 10 seconds. Therefore, since the heater chip is heated to 288 ° C. or higher in both the primary and secondary heating during heating, the printed wiring board is soldered under extremely severe conditions. As a result, there is a problem in that the quality of the product becomes unstable because the printed wiring board itself is likely to be deteriorated or deteriorated, or the pad is likely to be peeled off.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and when reflow soldering a surface mount type component by an instantaneous heating method, a printed wiring board may be deteriorated or deteriorated by high heat. It is an object of the present invention to provide a method for soldering a printed wiring board, which can stabilize the quality without causing peeling of the pad.

[0009]

According to the present invention, the object is to position and hold a surface mount type component on the upper surface of a printed wiring board, and press a momentary heating type heater chip from above onto the soldering portion of the component for reflow soldering. Method, the printed wiring board has a thermal conductivity of 6 × 10 ⁻⁴ to 18 × 10 ⁻⁴ C.
It is achieved by a method for soldering a printed wiring board, which is characterized in that the reflow soldering is carried out by placing it on a table made of resin of al / cm · sec · ° C. Here, it is preferable that the heating of the heater chip is performed in two stages of preheating and main heating.

[0010]

FIG. 1 is a process diagram of an embodiment of the present invention, and FIG. 2 is a perspective view of a heater chip and parts. In FIG. 1A, reference numeral 10 is a thin printed wiring board having a thickness of about 0.2 mm. This printed wiring board 10 is obtained by etching a circuit pattern of a copper foil on both surfaces of an insulating laminated board obtained by stacking sheets (prepreg) in which a substrate such as glass fiber is impregnated with a polyimide resin having excellent heat resistance and pressurizing and heating. It was formed. In this figure, 12 and 12 are pads formed by this circuit pattern, that is, soldering portions.

The pads 12 and 12 are shown in FIG.
As shown in, the cream solder 14, 14 is supplied. The cream solders 14 and 14 can be supplied by a printing method by overlaying a metal mask (not shown) on the upper surface of the printed wiring board 10. Alternatively, a computer-controlled dispenser that sequentially supplies a predetermined amount to a prestored supply position may be used.

A surface mount type component 16 such as an IC is fixed to the printed wiring board 10. For example, the flat package type having the surface mounting leads 18 on the opposite two sides or four sides is fixed to the surface of the printed wiring board 10 by fixing the leads 18 to the pad 12 by the viscosity of the cream solder 14 itself. ((C) of FIG. 1).

This printed wiring board 10 is shown in FIG.
It is placed on the table 20 as shown in FIG. This table 20 is 6 × 10 ^-4 to 18 × 10 ^-4 Cal / cm · sec ·
It is made of resin having a thermal conductivity in the range of ° C. For example, a phenol resin plate suitable for protecting the circuit pattern on the lower surface of the printed wiring board 10 can be used. In this case, especially for the thin printed wiring board 10 having a thickness of 0.2 mm, the thermal conductivity is as small as 7.5 to 8.5 in the above range.
× 10 ^-4 Cal / cm · sec · ° C is desirable.

As the table 20, a plate made of asbestos-filled melamine resin, glass fiber-filled silicone resin, cellulose-filled formalin resin or the like can be used in place of the phenol resin plate. Further, it is desirable that the thermal conductivity be selected so as to increase as the thickness of the printed wiring board 10 increases, for example. That is, as the thickness increases, the heat from the heater chip 22 is less likely to escape, and the temperature near the pad 12 is likely to rise.

In this way, the table 20 of the predetermined thermal conductivity is obtained.
After the printed wiring board 10 is placed on, the heater chip 22 is pressed against the lead 18 from above as shown in FIG. As shown in FIG. 2, the heater chip 22 has a pressing portion 22A that presses the leads 18 arranged in a line at a time, and the electrode portions 22B and 22B are provided from both ends of the pressing portion 22A.
Is rising. The electrode parts 22B, 22B are attached to an elevating device (not shown) and move up and down. The temperature of the heater chip 22 is detected by a thermocouple 24 fixed near the center of the pressing portion 22A.

The heater chip 22 generates heat by passing a current between the electrode portions 22B and 22B while pressing the lead 18. This electric current is controlled so that the temperature detected by the thermocouple 24 falls on a predetermined control pattern. Eg 30
After heating at 0 ° C for 9 seconds (primary heating, preheating), immediately start heating at 450 ° C for 5 seconds (secondary heating, main heating), and then stop energization.

At this time, the temperature of the leads 18, the pads 12, and the printed wiring board 10 becomes sufficiently lower than the temperature of 300 ° C. or 450 ° C. This is because the printed wiring board 10 is placed on the table 20 having an appropriate thermal conductivity, and when the heater chip 22 is pressed, the printed wiring board 10 is brought into close contact with the table 20 due to this pressing force.
This is because the heat of is quickly diffused to this table 20.

At this time, the thermal conductivity of the table 20 is set in consideration of the respective temperature gradients inside the leads 18, the pads 12 and the printed wiring board 10, but as a result of the experiment, the above range, that is, 6 × 10 ^-4 to 18 × 10 ^-4 Cal
It has been found that it is desirable to set / cm-sec- ° C.
If the thermal conductivity of the table 20 is too high, the temperature of the soldering portion does not rise sufficiently and the soldering is likely to be incomplete. On the other hand, if the thermal conductivity is too low, the soldered portion becomes too hot, and the peeling of the pad 12 and the alteration and deterioration of the printed wiring board 10 are likely to occur.

When the soldered portion is heated to an appropriate temperature without being overheated or underheated in this way, the cream solder 14 is melted and as shown in FIG. 1 (E). The lead 18 is normally soldered to the pad 12.

In the above embodiment, in the case of the printed wiring board 10 made of polyimide resin having a thickness of 0.2 mm, 7.5 to 8.
Although a phenol resin plate of 5 × 10 ⁻⁴ Cal / cm · sec · ° C. was used as the table 20, it is desirable that the material and thermal conductivity of the table 20 be appropriately changed depending on the thickness and material of the printed wiring board 10. Of course, it is generally desirable to increase the thermal conductivity of the table 20 as the printed wiring board 10 becomes thicker.

Further, it is desirable to change these according to the heating control pattern of the heater chip 22. For example, it is desirable to increase the thermal conductivity of the table 20 within the set range described above as the temperature of the heater chip 22 increases and as the heating time increases. The present invention is generally preferably applied to a thin printed wiring board 10, and is suitable for, for example, one having a thickness of 0.4 mm or less.

[0022]

As described above, according to the present invention, when the surface mount type component is reflow soldered by the instantaneous heating method,
Set the table on which the printed wiring board is placed to 6 × 10 ^-4 to 18
Made of resin with a thermal conductivity of × 10 ^-4 Cal / cm · sec · ° C, the heat of the heater chip is appropriately dissipated from this table, and at this time the soldered part can be kept at an appropriate temperature. .. Therefore, it is possible to prevent problems such as deterioration or deterioration of the thin printed wiring board due to overheating and peeling of the pad.

[Brief description of drawings]

FIG. 1 is a process chart of an embodiment of the present invention.

FIG. 2 is a perspective view of a heater chip and parts.

[Explanation of reference numerals] 10 printed wiring board 12 pad 14 cream solder 16 surface mount type component 18 lead 20 table 22 heater chip

Claims (2)

[Claims] 1. A method of positioning and holding a surface mount type component on an upper surface of a printed wiring board, and pressing a heater chip of an instantaneous heating system from above onto a soldering portion of the component to perform reflow soldering. Thermal conductivity is 6
A method for soldering a printed wiring board, which comprises placing on a table made of a resin having a temperature of × 10 ^-4 to 18 × 10 ^-4 Cal / cm · sec · ° C and performing the reflow soldering. 2. The method for soldering a printed wiring board according to claim 1, wherein the heater chip is temperature-controlled so that the soldering portion is preheated and then main heating is continuously performed.