JPS60182191A - Printed circuit board for soldering laser - 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 [Technical Field] The present invention relates to printed wiring boards to which smear components are soldered by radar heating.

[Prior art]

A method of soldering electronic components to a printed wiring board using a laser heat source is already known in JP-A-54-63371 and JP-A-55-30895. In addition, as a problem with this laser soldering, Japanese Patent Application Laid-Open No. 57-841
93 states that if the laser beam directly hits a part of the board that does not need to be heated within the radar irradiation part, the board material will be burnt out.As a means to prevent this, through holes are made in the part of the board that does not need to be heated. It is disclosed that the laser beam is allowed to pass through the laser beam.

Further, Japanese Patent Laid-Open No. 58-64782 discloses a method for soldering by operating an insulating substrate at a constant speed and continuously irradiating it with laser light for the purpose of improving production efficiency. As a problem in this case, it has been reported that the board burns out, and in order to prevent this, a burnout prevention plate made of a material with a high reflectance of laser light is placed between the laser beam and the soldering area. A method is disclosed.

On the other hand, the conventionally used CO2 laser (wavelength 1O
In recent years, YAG radar (wavelength 1.0
The reason why 6μ) has come to be frequently used as a heat source for soldering is that the YAG laser, which has a shorter wavelength, has a lower CO2
It has a higher absorption rate for gold-flexible phase materials than a laser, and a higher transmittance for substrates made of epoxy resin, etc.
This is because there will be fewer burnout accidents. However, on the other hand, in order to perform high-speed soldering and fine soldering that take advantage of the original characteristics of laser soldering, the trend is to use high-energy density lasers in the future, and measures to prevent board burnout will continue in the future. This is likely to become a more important technical issue.

However, the above-mentioned Japanese Patent Application Laid-Open No. 57-84193. Japanese Patent Application Publication No. 5
Applying the content disclosed in JP-A-8-64782 to the case where a large number of electronic components and printed wiring boards are soldered together, the method of JP-A-57-84193 can be used to solder a large number of electronic components and printed wiring boards. The number of through-holes increases, and when there are many types of component parts, it is necessary to vary the shape and position of the through-holes, and extremely complicated drilling requires expensive work or punching. A mold is required. Also, if you think about JP-A-58-64782, if there are many types of parts used and a large number of parts used, it is necessary to prepare a complicated burnout prevention plate corresponding to each type, and in the case of actual work, it is necessary to prevent burnout. It requires precise alignment between the board and the printed wiring board.

[Purpose of the invention]

The present invention solves the above-mentioned drawbacks of the conventional technology, and eliminates the need for many man-hours and expensive molds and jigs in laser soldering between electronic components and printed wiring boards, which are used in large quantities. The purpose of the present invention is to provide a printed wiring board that can easily prevent burnout. Laser soldering is accomplished with printed wiring boards that are coated with a solder resist that is more reflective than the wiring board.

[Real ellipse mode]

Hereinafter, the implementation of the present invention will be explained with reference to the accompanying drawings.

1 to 3 are diagrams for explaining one embodiment of the present invention, in which 1 (d: electronic components, 2-digit electrode parts, 3-digit wiring formed on the upper part of the printed wiring board 4). Pattern 5 is a laser beam.

As shown in FIG. 1 and FIG.
The laser beam 5 is attached to one side of the fallen wiring pattern 3, and the laser beam 5 is applied to the shaded area in FIG. 1 and 2 in FIG. 2.
When irradiating the area indicated by two arrows, wiring pattern 3
If the laser beam hits the part 6 of the board that has come loose (the part painted black in Figure 1), this part will be burnt out. (The blacked out area in Figure 2) Therefore, as shown in Figure 3, the wiring board surface, including at least this area 6, has a high reflectivity for the radar beam 5, as well as the wiring board base material. By applying the solder resist 7, the irradiation range of the temporary beam is wide, and even if the irradiation position is slightly shifted, the wiring board will not be burnt out. In addition, since printing solder resist has been conventionally done, there is no need for additional steps in terms of work. Not needed at all.

Next, the structure of the solder resist used in the present invention, such as the solder resist 7, will be explained.

Figure 4 shows the infrared absorption bands of epoxy resins described in the Handbook of Analytical Chemistry edited by the Japanese Society of Analytical Chemistry. Although wavelengths below 2μ do not appear in the diagram, it is generally said that there is no absorption band. As can be seen from this figure, the transmittance of the epoxy resin to the YAG laser having a wavelength of about 1 μm is about 90%. Therefore, if you use a commercially available epoxy resin solder resist material, it will hardly prevent the board from burning out, and it is possible that the full dare nost material itself may be burned out due to the added pigments and other contaminants. .

Generally, in order to improve the reflectance of such materials, a method is used in which the binder material is filled with a substance that has a good reflectance for laser light.
slcs, Hand Book I 957 f'-ta indicates the reflectance of light on a metal surface. Pb-8n solder is commonly used as a solder material, and Pb
, Sn M YAG laser (1,06/4 wavelength) has a much lower reflectance than a CO2 laser (10,6μ wavelength). However, even in YAG lasers, Ag+Cu, AA, etc. have higher reflectance than Pb+Sn, so it is necessary to fill these materials into a polymer binder such as epoxy resin or butadiene rubber to form a solder resist material with high laser reflection efficiency. I can do it. Needless to say, if the reflectance is high, the above-mentioned oxide or other insulating material is more preferable as the material constituting the solder resist.

In addition, when performing continuous large amounts of soldering by moving the printed wiring board at a constant speed and continuously irradiating laser light,
It is preferable to apply the solder resist according to the present invention to the surface of the printed wiring board or to the electronic components other than the parts that do not require heating in the laser irradiation part of the printed wiring board.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the printed wiring board from being burnt out by the laser only by applying the solder paste with high laser reflectance as described above, so it is possible to prevent the printed wiring board from being burnt out by the laser. Therefore, it is particularly suitable when laser soldering is performed one after another. Further, in this case, soldering can be said to be an extremely advantageous method in terms of cost since it does not require expensive molds or jigs.

[Brief explanation of the drawing]

FIGS. 1 to 3 are diagrams for explaining one embodiment of the method of the present invention, and FIGS. 4(a) and 4(b) show liquid Nyxy resin (molecular weight approximately 355) and solid epoxy resin (molecular weight approximately 355), respectively. FIG. 5 is an infrared absorption spectrum diagram of the molecular weight of about 1400), and FIG. 5 is a diagram showing the reflectance of infrared rays on the metal surface. ■...Electronic parts, 2...City, polar part, 3...Wiring/turn, 4...Printed wiring board, 5...Laser beam, 6...Part not requiring machining, 7...・Nrugurenost ・
Figure 3

Claims (4)

[Claims] (1) In printed wiring boards to which laser-heated parts are soldered, at least the part of the printed wiring board that does not require heating in the laser irradiation area has a reflectance of the printed wiring board base material in the laser wavelength range. Laser soldering is for printed wiring boards characterized by a high solder resist being applied. (2) A printed wiring board for laser soldering according to claim 11, wherein the solder resist is made of a polymeric material filled with laser reflective material powder. (3) A printed wiring board for laser soldering according to claim (2), wherein the laser reflective material powder is a metal powder. (4) The printed wiring board for laser soldering according to claim (2), wherein the metal powder is Ag, Cu, or At powder.