Solder mask

Solder mask, solder mask, soldermask or soldermask met on a circuit board for electronic circuits different functions. It serves to protect the circuit board from corrosion, mechanical damage, and prevent the wetting of the solder -coated with it on surfaces of the circuit board. Furthermore, improved solder electrical properties such as dielectric strength. He was especially developed for wave soldering to prevent solder bridges and to reduce the Lötzinnverbrauch. The most common color is green, but many other colors are possible. As a material for solder comes as epoxy resin in question.

The solder resist should harmonize with the flux and cleaning agents used.

Application process

The application process will be determined by the nature of the solder resist. There are two major groups of solder resists.

  • Photostructurable solder resists (LPI, liquid photo imageable soldermask )
  • Not photostructurable solder resists

The non photostructurable solder resists are cured either thermally or by UV light. They are applied by screen printing method using structured sieves.

The photostructurable solder resists are viscous liquids or photopolymer films in the form of a dry film. All photostructurable solder resists are negative-working. After the application, they must be dried, exposed and developed.

The photopolymer films are applied by lamination. Their importance is presently fallen sharply.

In practice, the following methods are applied to printed circuit boards to be coated with solder mask:

  • Screen printing ( screen printing )
  • Spraying ( spraying )
  • Curtain coating ( curtain coating )
  • Roller application ( roller coating)

From each of these methods, there are different variants and versions with advantages and disadvantages, so it is not possible to speak of an optimal coating process.

Screen printing

In screen printing, the solder resist is pressed by the doctor through a sieve. Here, vertical and horizontal screen printing systems can be distinguished.

Screen printing is performed horizontally or vertically sided double-sided. On one needle bed, it is also possible to coat on both sides horizontally at screen printing.

Spraying

Spraying will also be divided into vertical and horizontal alignment process according to the circuit board. It also distinguishes between electrostatic spraying and conventional spraying.

Inkjet technology

A novel method for the application of solder resist, the ink jet technology. This procedure is still in development.

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