JPH0575196B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention [Field of Industrial Application] The present invention relates to a printed wiring board suitable for laser soldering.

[Conventional technology]

In the past, the so-called flow method was generally used as an efficient method for attaching various electrical elements such as IC chips, resistors, capacitors, and other components to the required parts of the wiring pattern of a printed wiring board by soldering. ing.

The reflow method allows for mass production since it is possible to solder a plurality of components at once, and the soldering conditions of individual components are generally highly reliable. Moreover, due to the technique, a considerable amount of heat is applied to all the parts to be attached, so in practice, only heat-resistant parts are soldered using the reflow method, and then heat-sensitive parts are soldered by hand as retrofitted parts in two steps. Installation of all parts has been completed during processing. It is inefficient to manually solder heat-sensitive parts as retrofitted parts, and the reliability of the product varies depending on the level of skill of the operator. Therefore, the advantages of the reflow method are not fully utilized.

Also, due to the arrangement of other parts previously attached in the reflow process, the tip of the soldering iron may not fit in, making it impossible to solder later parts by hand.
Furthermore, it has been impossible to reflow a product that has been reflow-treated once again as necessary.

Therefore, a soldering process using laser beam scanning is recommended as a method for rationally and mass-producing soldering of multiple components to each required part of the wiring pattern of a printed wiring board without the above-mentioned problems. .

That is, as the substrate 1 (base board, FIG. 2) of the printed wiring board, a material plate substantially transparent to laser light (non-laser light absorbing), such as glass epoxy, polyimide, ceramic, etc., is used. A required printed wiring pattern 2 (metal pattern such as copper foil) is formed on one surface of the substrate to form a printed wiring board. Reference numerals 2a and 2b are a line pattern portion of the wiring pattern 2 and a pad pattern portion serving as a soldering seat for a terminal of a component to be attached. Place an appropriate amount of cream solder 3 on the surface of each pad pattern portion 2b. A predetermined part to be attached 5 is placed between a predetermined pad pattern portion or between predetermined pad pattern portions.
By placing the component terminals 5a in contact with the cream solder 3 on the pad pattern portion, all required components 5 to be mounted are placed on the printed wiring board.

Next, the printed wiring board surface portion along the irradiation path 6 is scanned with a laser beam 7 having a predetermined beam diameter d (the laser beam device is omitted from the figure), using the line connecting the pad pattern portions 2b to each other as an irradiation path 6. The intensity, scanning speed, beam diameter d, etc. of the scanning laser beam 7 are determined by taking into account the size of each pad pattern 2b, the amount of cream solder 3 placed on it, the size of the terminal 5a of the attached part 5, etc. Appropriate settings are made in advance. 7a is the scanning start position of the laser beam 7 on the printed wiring board (laser beam 7
(warming-up position).

Since it takes a certain amount of time for the output of the laser beam device to rise to a predetermined level and become stable, the output laser beam during the warming-up period of the device is irradiated onto the surface of the printed wiring board at the scanning start position 7a. After the output stabilizes, the position 7a
Laser beam scanning along the irradiation path 6 is started.

Of the printed wiring board surface portions subjected to laser beam scanning along the irradiation path 6, each pad pattern portion 2b of the printed wiring 2
In the area A where the irradiated laser beam exists, the energy of the irradiated laser beam is absorbed by the pad pattern 2b, the cream solder 3 thereon, and the terminal 5a of the mounted component 5, which are non-transparent to the laser beam, and generate heat, causing The cream solder 3 is melted and the pad pattern portion 2b and the component terminal 5a are properly soldered. Solder 3 once melted
begins to solidify when the laser beam 7 passes through it.

The area portion B where the line pattern portion 2a of the printed wiring 2 exists is also the line pattern portion 2a.
Since it is not laser beam transparent, it absorbs the energy of the irradiated laser beam and generates heat.

Since the substrate 1 is transparent to the laser, substantially no heat is generated in the area C of the printed wiring board 1 where neither the pad pattern portion 2b nor the line pattern portion 2a is present.

Thus, according to the laser soldering method as described above, all the parts 5 to be soldered and attached to the printed wiring board, including the heat-sensitive parts, can be soldered at once, which improves workability and mass production. The soldering conditions of the individual parts 5 are also highly reliable overall. It is also possible to solder a product that has already been soldered once again if necessary. When retrofitting a specific component as necessary, it is possible to solder in a narrow area where the tip of a soldering iron cannot fit, in the case of related attachment such as an arrangement of neighboring components that have already been soldered. be.

[Problem that the invention seeks to solve]

By the way, in the laser soldering method as described above, area portion B of the printed wiring board surface portion (the wiring board surface irradiation path area of the laser beam) that receives laser beam scanning along the laser beam irradiation path 6, that is, the printed wiring 2 track pattern part 2a
The area B where B exists has nothing to do with soldering and does not need to generate heat; however, as described above, due to the presence of the line pattern portion 2a that does not transmit laser light, the energy of the laser beam is absorbed in the portion 2a. Heat is generated by the absorption of

The intensity and scanning speed of the scanning laser beam 7 are set to be suitable for properly soldering the pad pattern portion 2b and the component terminal 5a in each area A to be soldered, and the scanning laser beam 7 is When the printed wiring board is scanned with a laser beam along the printed wiring board, the energy of the laser beam 7 irradiated on the area A is applied to the pad pattern portion 2b existing there.
The energy of the irradiated laser beam 7 is absorbed in the solder cream 3 and the component terminal 5a in a predetermined temperature range to achieve good soldering overall. It is intensively absorbed only in the existing line pattern portion 2a,
As for only the line pattern portion 2a, the amount of action energy of the irradiated laser beam 7 is excessive, and as a result, the line pattern portion 2a may overheat and burn out of the pattern portion.

In the laser beam scanning process along the irradiation path 6, during the scanning process of each area A, the strength is adjusted to be suitable for soldering the pad pattern part 2b of that area and the component terminal 5a, and other areas. It is conceivable to control the intensity of the output laser beam 7 so that it becomes weaker during the scanning process of parts B and C, but each time the output is changed, there must be time for the beam output to stabilize. As a result, the overall scanning processing speed is significantly reduced, making it practically impractical.

The present invention adds a device to the aspect of the wiring pattern 2 formed on the printed wiring board side for laser soldering,
The purpose of this invention is to strictly prevent the occurrence of the above-mentioned burnout trouble in the line pattern portion 2a of the wiring pattern 2, and to improve the reliability of efficient and mass-produced soldering processing using the laser beam scanning method.

B. Structure of the Invention [Means for Solving Problems] The present invention provides a printed wiring board for laser soldering in which a printed wiring pattern on a board surface is scanned with a laser beam for soldering processing of terminals of components to be attached. The object of the present invention is to provide a printed wiring board characterized in that a pattern part other than the pattern part is formed so as to be located outside the wiring board surface irradiation path area of a scanning laser beam.

[Effect]

That is, by forming the printed wiring pattern on the board surface in advance in the pattern form described above, the parts of the printed wiring pattern other than the part of the printed wiring pattern that is subjected to laser beam scanning for soldering processing of the parts to be attached are It is not irradiated with a laser beam, and therefore, the above-mentioned burning problem of the pattern portion due to unnecessary laser beam irradiation on the pattern portion is strictly prevented.

〔Example〕

FIG. 1 shows one embodiment, and members and portions common to those in the example shown in FIG.

2c indicates the existence of a line pattern portion 2a in the area irradiated by the laser beam on the wiring board surface in the example shown in FIG. area portion B and the line pattern portion 2a
is a portion formed as a detour line pattern outside the laser beam irradiation path on the wiring board surface by avoiding this area according to the present invention. Therefore, the region B in the example of FIG. 2 becomes the region C of only the printed wiring board 1 in which neither the pad pattern portion 2b nor the line pattern portion 2a exists in the example of FIG.

Then, as in the past, cream solder 3 is placed on each pad pattern portion 2a of the wiring pattern 2, and a predetermined component 5 to be mounted is connected between the predetermined pad pattern portions in a predetermined pad pattern region by connecting the component terminal 5a with the pad pattern. All the required components 5 to be mounted are placed on the printed wiring board by placing them in contact with the cream solder 3 on the parts, and the lines connecting the pad pattern parts 2b to each other are set as the irradiation path 6 and are placed in the irradiation path. A laser beam 7 is scanned along the printed wiring board surface.

As a result, in each pad pattern portion 2b, the cream solder 3 that is left on the pad pattern portion 2b is melted, thereby achieving good soldering between the pad pattern portion 2b and the component terminal 5a.

Further, since there is no printed wiring pattern portion such as the line pattern 2a other than the pad pattern 2b which is a soldering point within the irradiation area of the wiring board surface of the laser beam 7, there is no possibility that the pattern portion will be burned out by the laser beam.

C. Effects of the Invention As described above, according to the present invention, the strength of the laser beam output can be controlled to prevent the problem of burnout of the printed wiring pattern portion 2a unrelated to soldering caused by irradiation of the laser beam to the pattern portion 2a. This can be strictly prevented with a simple and unnecessary treatment structure. Since it is possible to make the laser beam irradiation path (scanning path) on the wiring board surface a simple path connecting each soldering point in the shortest possible time, the soldering speed can be increased, and printed wiring boards using the laser beam scanning method can be used. The soldering process can be performed reliably in mass production at low cost, and the intended purpose is well achieved.

[Brief explanation of the drawing]

FIG. 1a is a plan view of a part of the wiring board according to the present invention, FIG. 1b is a sectional view taken along the line b-b of FIG. 1a, and FIG. FIG. 2b is a plan view of a part of the wiring board with a printed wiring pattern that may occur, and FIG. 2b is a sectional view taken along the line bb--b of FIG. 2a. 1 is a printed wiring board, 2a to c are printed wiring patterns, 3 is cream solder, 5 is a mounted component, 5a is a component terminal, 6 is a laser beam irradiation path,
7 is a laser beam.

Claims (1)

[Claims] 1 In printed wiring boards for laser soldering,
The printed wiring pattern on the board surface is formed in such a manner that the pattern part other than the pattern part that is scanned by the laser beam for the soldering process of the terminal of the component to be mounted is located outside the irradiation path area of the wiring board surface of the scanning laser beam, A printed wiring board characterized by: