Peelable glue performance and quality control of aluminum substrate, circuit board, PCB

During the hot air leveling process for circuit boards, aluminum substrates, and circuit boards, some boards have gold-plated parts, such as gold fingers. When tin-plating, protect the gold fingers to prevent the gold fingers from being tin-plated. So how to do it? At this time, peelable glue is used, and covered with peelable glue in the gold-plated place. In addition, there is another method is to use high temperature resistant glue to cover and cover. , Peelable rubber has considerable technical and economic advantages. If it is suitable for mass production, it saves time; it is easy to peel without adhesive; suitable for high-precision boards, which can better cover and protect difficult areas; therefore, high-precision boards are generally peelable. But high temperature resistance Glue has the advantages of simple process and does not need screen making, so some boards with low precision requirements can be used. The following is a brief introduction to the performance of peelable glue and the issues to be noticed.

Peelable, as the name suggests, is a temporary coating. When the specified plating or tinning is completed, it can be easily stripped. A qualified strippable adhesive can be completely stripped from the board without leaving marks or stains on the plated through holes or surfaces. It is a one-component screen printing ink.

The common problems of peelable glue in the operation process are mainly the difficulty of peeling or unclean peeling, incomplete covering and excessive covering.

Difficult peeling or poor peeling is caused by over-baking or insufficient printing thickness. Incomplete cover is caused by inaccurate registration during printing, and excessive cover is caused by inaccurate registration, too low screen mesh, excessive pressure, and excessive printing times. So to solve these problems, we must start from these aspects.

The temperature of the peelable drying shackle is generally controlled at about 150 ° C, and the time is about half an hour. Excessive temperature or time will cause peeling difficulties or uncleanness. The printing thickness depends on the specific situation, but generally should not be less than 300um, and the thickness of the thicker film layer when the copper surface is thicker, such as 2oZ The board is thicker than the 1oZ board when printing peelable. The thickness of a 2oz board is generally 700um.

Thickness control can be realized through the selection of screen mesh number, printing times and scraper angle. If you want to get a thicker film layer, you can choose a lower mesh screen and increase the number of printings. However, these two methods can easily cause too many missed prints, and the edges are not smooth, which will eventually lead to excessive covering. And sometimes adjusting the scraper angle can achieve twice the result with half the effort. We received such a complaint in July that the peelable adhesive we provided was not cleanly stripped. We went to the site for observation and analysis and thought that it was caused by insufficient printing thickness, because they printed 2oZ boards. After listening to the other engineer's introduction to their measures. We adopted adjusting the angle of the scraper to make the scraper more inclined, and printed twice based on this (not two scrapes at the same time, but a short baking of the first printing and then printing again). In this way, the printed film thickness can meet the requirements, and the edges are relatively smooth, without side effects such as excessive cover. After baking and tin spraying, it can be completely peeled and cleaned, which successfully solves the problem.

There is another principle that must be grasped when carrying out peelable printing, that is: the place to be covered must be covered, and the place that should not be covered must not be covered. Sometimes when printing on some high-precision boards, there will be over-covering. This problem can be improved by increasing the screen mesh number, reducing pressure and reducing the number of printing. Screen is generally selected between 10-24T / cm. Experience tells us that plain weave is more oily and smoother than twill.

I believe that as long as the above properties of the peelable rubber are mastered and controlled in operation, satisfactory results will be achieved.