JPS626795A - Flux for soldering - Google Patents

Abstract

PURPOSE:To decrease the defect in a solder coater treatment by adding a specific amt. of a thixotropic property applying material to a flux to be used for a surface packaging substrate. CONSTITUTION:The thixotropic property applying material is added at 1-50g/l to the flux in the case of subjecting a printed circuit board to the solder coating treatment. The material which applies the thixotropic property to the flux for soldering is exemplified by pulverous powder silica and besides said powder, various silicates, calcium carbonate, etc. are also used. The base resin of the flux is a polyalkylene glycol and the deriv. thereof, glycerol deriv. resin, etc. The flux is thus held to a prescribed thickness on the circuit board and the defects in the solder coater treatment are decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a soldering flux used in the manufacture of printed circuit boards, and more specifically to a soldering flux for soldering to printed circuit boards using a solder coater (solder repeller). Regarding the flux of r! be.

(Prior art) Normally, soldering with a solder coater is carried out as follows in step 1 - that is, a small amount of flux heated to room temperature to 40°C is applied to a printed circuit board whose copper surface has been pretreated and cleaned. Both are applied to a thickness of 0.1 mm or more, and 20
Immerse in a solder bath at 0 to 270°C for 1 to 10 seconds. When this board is pulled up from the solder bath, excess solder is removed from the printed board by blowing heated air at 180 to 230°C, and then the board is washed with water and dried to complete the soldering process.

In the past, most of the boards to be soldered were copper through-hole boards with many conductive holes, but recently advances in surface mounting methods have made it possible to create boards without null-holes and with a smaller net area. The number of boards that have a large number of very small parts (about 1 m x 1 ms) is increasing. Chips are often mounted on the surface of such boards, and it is expected that the number of boards will continue to increase in the future.

(Problem to be Solved by the Invention) When such a board is soldered using a solder coater, the 7 lux adhering to the board is brought into a solder bath and then heated air is blown through it. A board with holes allows the flux to escape properly and uniform soldering is achieved, but a board without through holes has no place for the flux to escape, and there are areas where the solder and copper cannot make sufficient contact within a given period of time. I can do it.

Particularly for substrates where most of the area is coated with solder resist and there are many small exposed copper areas,
It has the disadvantage that it tends to have parts where solder does not stick, parts where the solder is extremely thin even if solder is applied, and parts where the solder becomes wavy (a mixture of thick and thin parts).

In order to improve the solderability of such a board, the above-mentioned drawbacks can be overcome to some extent by adding a solvent to the flux, lowering the viscosity of the flux, and applying a thin coat of siflux. However, the coating was too thin, resulting in copper areas that were not completely covered by 7 lux.

New causes of defects occur, such as poor soldering and formation of solder durl on the solder resist.

(Means for Solving the Problems and Effects) The present invention is to impart thixotropic properties to the flux used for such surface mount boards. Ru.

This will be explained in detail below.

When solder coating a printed circuit board, the thickness of the flux is usually 0.1 or more, and if it is less than that, the solder finish will be poor and solder gel will form on the solder resist. Product is unusable.

The flux used for surface mounting boards has a 7.
The thickness of the flux is maintained at 0.1u or more, and the low viscosity flux is removed in a short time during soldering.
It is desirable to use something that makes good contact between the solder and the copper.

In order to satisfy this condition, the present inventors gave the flux thixotropic properties and maintained a predetermined thickness when applying the flux to the substrate.

The present invention was completed by successfully lowering the viscosity during soldering.

Finely powdered silica such as Erosil (manufactured by Degussa, West Germany) is a typical material that imparts such thixotropic properties to 7Lux for soldering, but in addition to this, various silicates, calcium carbonate, Thickeners such as bentonite-organic bentonite, talc, cellulose derivatives, polyvinyl alcohol, etc. can also be used. In addition, water, methanol, and ethanol are used as the solvent for the present invention.

Alcohols such as n-pronozonol, isopronol, n-butanol, isositanol, t-sitanol, ketones, glycols or their derivatives etc.
, a combination of one or more of these solvents is used. Base resins for the flux used in the present invention include polyalkylene glycols and derivatives thereof, glycerin derivative resins, water-soluble phenol derivative resins, etc. Examples of activators include amino acid hydrochlorides, amine hydrochlorides, and organic acids.

The addition amount of the thixotropic property imparting substance is difficult to numerically control the thixotropic property.

After actually treating a board with a solder coater and examining the solder adhesion failure rate, it was found that the following amount is preferable.

In other words, the amount of these thixotropic property-imparting substances added to the flux is preferably 1 to 50 g/l, and if it is less than 50 g/l, there is not much thixotropic property, and if it exceeds 509 g/l, no further effect can be expected. It is uneconomical in practical terms.

The present invention will now be explained in more detail with reference to Examples.O Examples A flux consisting of the ingredients of Prescription Examples 1 and 2 below was prepared.

Formulation example 1: 1 molecule of copolymer z6soo)s
s% deethylamine hydrochloride
5% water
20% Petyl Cello Sorzo
20% formulation example 2: Added 6% Erosil (manufactured by Degussa) to the flux of the above composition. 0.5 wx on one side of a printed circuit board manufactured by Matsushita Electric Works Co., Ltd.
Solder resist printing is performed so that there are 1000 copper surfaces of X1 bead corners.

Each of the fluxes according to the above prescriptions was applied to the substrate made in this way at 0.0%. Apply to a thickness of gIIj+ or more and use a solder coater (H3C-) manufactured by Inu Nippon Screen Manufacturing Co., Ltd.
224D), and the number of defective soldering of 1000 hook parts was measured.

We conducted an experiment 10 times with the same flux to check the solder adhesion failure rate, and found that the fluff of prescription example 1 had an average of 3.
The defective rate was 0%, but in the case of the flux of Prescription Example 2 according to the present invention, the defective rate was 0%.

(2 others)

Claims (1)

[Claims] A flux for soldering, characterized in that a thixotropic property imparting agent is added in an amount of 1 to 50 g/l.