JP2757743B2 - Manufacturing method of printed wiring board with solder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board used for electronic equipment and electric equipment. More specifically, the present invention relates to a method for immersing an insulated substrate having a copper circuit formed therein in a solder bath. The present invention relates to a method for manufacturing a printed wiring board with solder, in which hot air is blown onto the copper circuit while being drawn from a solder bath.

[0002]

2. Description of the Related Art A printed wiring board used in electronic equipment and electric equipment is manufactured by soldering in advance to a circuit on which components are to be mounted in order to prevent rust of a copper circuit and to improve solder familiarity during mounting. It has been known.

In the above-mentioned manufacturing method, after a flux is applied to an insulating substrate having a circuit formed on its surface, an end of the insulating substrate is gripped by an arm, immersed in a solder bath, and pulled out of the solder bath while being attached to the solder bath. Blow hot air from an air knife to remove excess solder. The thickness of the solder is adjusted by the pressure of the hot air blown. The insulating substrate to which the hot air has been blown is left for 5 seconds or longer, and is taken out when the temperature of the substrate becomes 150 ° C. or lower. However, if post-mounting solder is applied to the printed wiring board that has been soldered in this manner, repelling occurs in which the post-mounting solder does not adhere, and the solder wettability is poor.

[0004] The cause of this is that a copper-tin alloy layer (Cu ₆ Sn ₅ , Cu
_{This is because if} 3Sn) is formed and the thickness of the solder is small, the alloy layer is exposed up to the surface of the solder. As a countermeasure for this, a method of increasing the thickness of the solder by weakening the pressure of the hot air to be blown can be considered. However, if the solder is too thick, as shown in FIG. Solder (2a) could not be removed,
There is a disadvantage that the thickness of the solder (2a) is uneven. If the thickness of the solder (2a) is uneven, bonding failure of the mounted component occurs. Therefore, there is a demand for a printed wiring board having a uniform solder thickness and good solder wettability.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a manufacturing method in which soldering is performed in advance on a circuit on which components are to be mounted. An object of the present invention is to provide a method for manufacturing a printed wiring board with solder having good solder wettability.

[0006]

According to the present invention, there is provided a method for manufacturing a printed wiring board with solder, comprising the steps of:
230-250 immersed in solder ° C., the the insulating substrate
While pulling out from the solder , 200-240
A method for blowing hot air at a temperature of ° C., characterized by rapidly cooling within 2 seconds after blowing the hot air.

[0007]

The amount of the alloy layer of copper and tin formed between the copper circuit and the solder increases as the high-temperature holding time increases. In the present invention, after blowing hot air,
When quenched within 2 seconds, the alloy layer of copper and tin is not formed on the surface of the solder, and the solder wettability can be improved. .

Hereinafter, the present invention will be described in detail. The present invention uses an insulating substrate on which a copper circuit is formed. Examples of the insulating substrate include an organic insulating substrate obtained by curing a prepreg resin obtained by impregnating and drying a base material with a resin, or a ceramic insulating substrate such as alumina. As the resin of the organic insulating substrate, an epoxy resin, a polyimide resin, a fluororesin, a phenol resin, an unsaturated polyester resin, a PPO resin, or the like alone, a modified product, a mixture, or the like is used. As the base material of the organic insulating plate, for example, glass, inorganic fibers such as asbestos, polyester, polyamide, polyvinyl alcohol, organic synthetic fibers such as acrylics, woven fabrics, nonwoven fabrics, mats made of natural fibers such as cotton,
Paper and combinations of these substrates are used. The copper circuit formed on the surface of the insulating substrate is not limited, for example, a circuit formed by etching a copper foil disposed on the surface of the insulating substrate, or a circuit formed by copper plating. Furthermore, through hole copper plating is applied to the insulating substrate as needed,
A copper circuit is formed in the through hole.

In the present invention, soldering is performed in advance on the insulating substrate on which the copper circuit is formed. This soldering method will be described with reference to the drawings. First, after the insulating substrate on which the copper circuit is formed is immersed in a water-soluble flux at 20 to 40 ° C., as shown in FIG. ), And immersed in the solder (2) in the solder bath (5). Next, FIG.
As shown in (b), hot air is blown onto the insulating substrate (4) from an air knife (6) provided on the solder tank (5) while pulling out from the solder (2) in the solder tank (5), Excess solder (2) is removed, and as shown in FIG. 2, a printed circuit board in which solder (2) is applied to copper circuit (3) is obtained. The thickness of the solder (2) applied to the copper circuit (3) is 1
５5 μm. The thickness of the solder (2) is controlled by appropriately adjusting the pressure of hot air blown from the air knife (6). If the pressure of the hot air is low and the thickness of the solder (2) exceeds 5 μm at the maximum, the thickness of the solder (2) will be uneven, resulting in poor connection of the mounted components. If the thickness of the solder (2) is less than 1 μm, an alloy layer of copper and tin generated between the copper and the solder will
The surface of the solder (2) is easily exposed. In addition, the insulating substrate
The temperature of the solder (2) into which (4) is immersed is 230 to 250.
° C. The temperature of the hot air blown from the air knife (6) is to 200-240 ° C.
Limited. If the temperature of the hot air is lower than 200 ° C., the solder (2) starts to solidify and is difficult to remove.

In the present invention, the hot air is rapidly cooled within two seconds after the blowing. The above-mentioned quenching method includes, for example, a method of immersion in a water tank. If quenched within 2 seconds, even if the solder thickness is as thin as 1 to 5 μm, the copper and tin alloy layer is not formed on the surface of the solder, and the solder wettability can be improved.

[0011]

EXAMPLE 1 A 1.6 m thick copper foil was placed on both sides as an insulating substrate.
m, a glass base epoxy resin laminate having a size of 260 × 260 mm was used. A copper circuit was formed on the surface of the insulating substrate by etching. The insulating substrate on which the copper circuit is formed is treated with a 30 ° C. water-soluble flux (W-
2304) for 10 seconds. Next, the end of the insulating substrate is gripped by an arm, immersed in a solder bath filled with 240 ° C. solder for 10 seconds, and pulled out from the solder bath while being placed on the solder bath. Hot air of 220 ° C from the air knife at a pressure of 3.0 kg / c
It was sprayed in m ^2. The distance between the air knife and the insulating substrate was 0.35 mm.

After blowing the hot air on the insulating substrate, the substrate was removed from the arm in 2 seconds, put into a water tank, and cooled to obtain a printed wiring board with solder.

The uniformity of solder thickness and solder wettability of the obtained printed wiring board were evaluated. For the evaluation of the uniformity of the solder thickness, the thickness of the solder was determined from the thickness of the copper circuit measured in advance with a micrometer and the thickness of the copper circuit after soldering. When the difference between the maximum and the minimum of the thickness of the solder was 4 μm or less, it was evaluated as ○, when it exceeded 4 μm, when it was less than 6 μm, Δ, and when it was 6 μm or more, ×.

For evaluation of solder wettability, a wave solder device was used. After applying post flux (MH-820V manufactured by Tamura Corporation) to the obtained printed wiring board with solder and floating it for 5 seconds at 240 ° C., the external appearance was visually observed. A circuit having no solder attached to the circuit and having repelling was rejected, and a circuit having no repelling was passed.

As shown in Table 2, the uniformity of the solder thickness was good and the solder wettability was good. Examples 2 to 4 The same insulating substrates as in Example 1 were used. The procedure was performed under the same conditions as in Example 1 except that the pressure of the hot air and the time from when the hot air was sprayed to when the hot air was injected into the water tank were as shown in Table 1, to obtain a printed wiring board with solder. The obtained printed wiring board with solder was evaluated for uniformity of solder thickness and solder wettability in the same manner as in Example 1.

As shown in Table 2, the uniformity of the solder thickness was good and the solder wettability was good. Comparative Examples 1 to 5 The same insulating substrates as in Example 1 were used. The procedure was performed under the same conditions as in Example 1 except that the pressure of the hot air and the time from when the hot air was sprayed to when the hot air was injected into the water tank were as shown in Table 1, to obtain a printed wiring board with solder. The obtained printed wiring board with solder was evaluated for uniformity of solder thickness and solder wettability in the same manner as in Example 1. The results were as shown in Table 2.

[0017]

[Table 1]

[0018]

[Table 2]

The printed wiring board with solder, which has been rapidly cooled within 2 seconds after blowing the hot air, has uniformity of solder thickness,
And the solder wettability was good.

[0020]

According to the manufacturing method of the present invention, a printed wiring board with solder having a uniform solder thickness and good solder wettability can be obtained.

[Brief description of the drawings]

FIG. 1 shows a solder bath used to carry out the method of the present invention;
It is the schematic which shows the front and back of the state which immersed the insulating substrate.

FIG. 2 is a sectional view of a principal part of a printed wiring board with solder obtained by the present invention.

FIG. 3 is a sectional view of a main part of a conventional printed wiring board with solder.

[Explanation of symbols]

 2 Solder 3 Copper circuit 4 Insulating board 5 Solder tank 6 Air knife 7 Arm

Claims (1)

(57) [Claims] 1. A 230 to the insulating substrate copper circuit is formed
A method of blowing hot air at 200 to 240 ° C. onto the copper circuit while immersing the substrate in the solder at 250 ° C. and pulling out the insulating substrate from the solder. A method for producing a printed wiring board with solder, characterized by rapidly cooling within the range.