JP2001291950A - Conductor surface treatment for circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductor surface treatment for circuit board, with which wet spreading of lead-free solder is improved, when fusing the solder. SOLUTION: An electroless plating layer 5 is formed on a conductor exposing surface 4 of a circuit board, the lead-free solder is stuck on this electroless plating layer 5, and a lead-free solder layer 6 is formed by fusing that lead-free solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a conductor surface of a circuit board, which improves the wettability and spreadability of the solder when the lead-free solder is melted.

[0002]

2. Description of the Related Art At present, as a method of surface-treating a conductor such as copper comprising a connection pad and a wiring pattern on a circuit board, a cream solder is printed in addition to plating means. Preliminary solder for melting the solder is generally known.

[0003] As a pre-treatment before the surface treatment of the conductor with preliminary soldering, pickling of the conductor surface for removing an oxide film and pre-flux coating as a rust preventive in addition to this pickling are performed. After the pre-processing, pre-soldering is performed,
The most commonly used solder at present is tin-lead alloy, that is, tin-lead eutectic solder.

[0004] The pre-soldered solder spreads on the surface of a conductor such as copper when the temperature is higher than the melting point in the melting furnace, and when the temperature is lower than the melting point, the center is hardened with the center slightly raised.
This is because tin-lead eutectic solder, which is most frequently used at present, is an alloy having a very good wettability to a conductor such as copper.

However, in recent years, lead is a harmful substance that causes pernicious anemia and knowledge impairment, and has been regarded as a problem as a substance that causes environmental pollution. Many solders used in electronic devices are tin-lead alloys. When water comes in contact with the lead, the lead is dissolved, but when the water is acidic, the amount of the lead dissolved out is extremely large. In the future, there is a possibility that the use of lead will be regulated in each country.Many industries, such as manufacturers, have started studying the use of lead-free solder, and the applicant has been evaluating lead-free solder as a spare solder. Was.

As a result, it has been confirmed that lead-free solder has very poor wettability as compared with tin-lead eutectic solder, and the solder is formed unevenly or there are places where the solder is not placed on the conductor surface. . Therefore, an attempt was made to improve the flux of lead-free solder and to improve the wettability using a nitrogen furnace, but no significant effect was obtained.

Therefore, the present invention has been made to solve the above problem.
An object of the present invention is to provide a method for treating the surface of a conductor of a circuit board, which improves the spreadability of the solder when the lead-free solder is melted.

[0008]

For this purpose, a method for treating a conductor surface of a circuit board according to the present invention comprises forming an electroless plating layer of silver or tin on the exposed conductor surface of the circuit board, After the cream-like lead-free solder is attached to the plating layer by printing or the like, the lead-free solder is melted.

Here, since the metal such as silver or tin forming the electroless plating layer is a metal used for lead-free solder, a special alloy layer is not formed on a conductor such as copper. It diffuses into the solder during the melting process.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in further detail with reference to the illustrated embodiments. FIG. 1 is a process chart of a method for treating a conductor surface of a circuit board according to the present invention, as shown in FIG.
First, a required conductor layer 2 consisting of connection pads and wiring patterns required as a circuit board is formed on a suitable insulating base material 1 in accordance with a conventional method. A surface protective layer such as a film or a resist layer 3 is formed, and thereby a conductor pad exposed surface 4 of a connection pad or a wiring pattern portion is formed at a predetermined position of the conductor layer 2.

The exposed conductor surface 4 may be subjected to a pickling treatment as a pretreatment if necessary, and then a metal such as silver or tin is used for the exposed conductor surface 4 as shown in FIG. The electroless plating layer 5 is formed by the electroless plating means.

Since the metal such as silver or tin forming the electroless plating layer 5 is a metal used for lead-free solder, a special alloy layer is not formed on the conductor layer 2 such as copper. Are diffused into the solder during the melting process.

Therefore, a lead-free cream solder is adhered on the electroless plating layer 5 by printing means, and the solder is melted to form a lead-free cream solder as shown in FIG. The lead-free solder layer 6 in which the metal of the electrolytic plating layer 5 is suitably diffused can be formed.

Since the lead-free solder layer 6 has good wettability with respect to the conductor layer 2, its appearance is as good as that of a conventional tin-lead alloy solder containing a lot of tin-lead eutectic solder.

[0015]

In the method for treating the conductor surface of a circuit board according to the present invention, the plating layer for improving the wettability of the lead-free solder to the conductor layer can be formed by electroless plating means. There is no need to provide a node.

Further, since the existing atmospheric melting furnace can be used as a means for melting the lead-free solder, it is unnecessary to newly invest in equipment such as a nitrogen furnace.

Since the metal such as silver or tin forming the electroless plating layer is a metal used for lead-free solder, no special alloy layer is formed on the conductor layer such as copper. It is suitable because it diffuses into the solder during the melting process.

Therefore, the present invention is most suitable as a conductor surface treatment means for forming lead-free solder as spare solder for connection pads and wiring pattern portions on a circuit board.

[Brief description of the drawings]

FIG. 1 is a process diagram of a method for treating a conductor surface of a circuit board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation base material 2 Conductive layer 3 Surface protective layer or resist layer 4 Conductor exposed surface 5 Electroless plating layer 6 Lead-free solder layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Osamu Mizuguchi 757 Tenhoki, Kusazaki-cho, Inashiki-gun, Ibaraki Pref. BB24 BB25 BB34 BB71 DD33 FF16 GG18

Claims (3)

[Claims] An electroless plating layer is formed on an exposed conductor surface of a circuit board, and a lead-free solder is adhered on the electroless plating layer, and then the lead-free solder is melted. Conductor surface treatment method for circuit boards. 2. The electroless plating layer according to claim 1, wherein the electroless plating layer is formed of silver or tin metal used for the lead-free solder.
Surface treatment method for circuit boards. 3. The method according to claim 1, wherein the lead-free solder adhered on the electroless plating layer is applied in a creamy state by printing means.