In this paper, a strippable adhesive is used instead of a special tape as a protective layer for gold plating and hot air leveling, and a process using strippable rubber is studied.

Keywords: peelable adhesive porosity

I. Introduction

Pin gold plating and hot air leveling are two important processes in the production of printed boards, and some parts that do not need to be processed need to be protected. In the past, special tape was used as a protective layer for plating and hot air leveling. However, this method has the disadvantages of high cost, long production cycle (for mass production), residual glue residue, influence on the appearance of the board surface, and the like. At present, some companies in the coastal area have used peelable adhesive instead of adhesive tape. It has a protective function of special adhesive tape in gold plating and hot air leveling. The peelable adhesive also has the following advantages: the cost is greatly reduced, the operation is simple, there are no residual marks and stains, and it is convenient for mass production. The cost has already been placed in a very important position for each PCB industry, and reducing costs is a concern for everyone. Therefore, peelable adhesives must have certain application prospects. Our factory has also started some exchanges.

Second, some features of peelable rubber

Peelable adhesive is a one-component screen printing protection ink with a solid content of 100% and a blue, viscous liquid. It can be used as a protective layer in electroplating to protect parts from electroplating and solder lead. The role of peelable glue is to replace tape as a protective layer. Because it is a temporary coating, it is completely peeled off at the end.

Third, the process

Use strippable process:

Fourth, the operating point

To make peeling easier, the printed board is cleaned prior to coating to remove grease and stains. Use a special cleaning agent when cleaning.

Since the peelable adhesive is a viscous liquid with a certain viscosity, it is generally coated with screen printing. The use of screens below 18T and 60-degree round polyurethane blades ensure that the peelables have a certain thickness to facilitate stripping.

Generally, no diluent is used for coating. In order to make the glue have a certain thickness, it is required that the angle of attack of the blade be 45-55 degrees during coating. In order to ensure a one-hundredth percent hole-closing rate, the speed of the knife is required to be slower than usual, or it will not be able to protect it.

The coating has to achieve the following effects: the peelable glue on the board surface is even and must have a certain thickness; the portion of the glue that flows into the hole is two-thirds to one-third of the hole depth, and it must be remembered when printing the first side. Flow into the other side to form a "rivet." Otherwise it will be difficult to peel off.

The degree of drying and curing has a great influence on the peeling. Generally, it is cured in a hot air circulating oven at 140° C. for 20-30 minutes. After curing, the peelable rubber should have high internal stress and elasticity. Over-curing and under-curing can not achieve the best peeling effect.

V. Conclusion

Through many tests, we found that the strippable performance is very stable and has good adhesion with the solder mask. For the difficult problem of stripping, we have played a very good role by changing the screen printing method, changing the screen of different meshes, using different hardness scrapers, and adjusting the curing time, and the stripping effect has been improved.

In the gold plating process of the pin, the protective effect of the peelable glue on the hole and the part that does not need to be electroplated can be found, no penetration of the gold plating liquid is found, and the gold-plated pin part can be protected during the hot air leveling process, and no peelable glue can be peeled off at a high temperature. At the same time, there is no tin-lead adhered to the gold foot. It can be seen that the peelable adhesive can withstand high temperatures.

The cost of peelable adhesives is greatly reduced compared to the use of special protective tapes, as well as their own good performance, so their application is also quite extensive.