1. Liquid ink imageable solder resists
This is also known as a liquid imaging solder resist (LPSM). It is a type of solder resist made from an ink formulation.
The following points define how LPSM or LPI solder resists work:
Application process
There are three (3) different ways to maximise the use of the LPI process for solder resist application. The first method is through silkscreen printing. As well as being one of the most affordable processes, it requires the liquid component to be mixed prior to application, as this extends the shelf life.
The second method is to spray the solder resist ink onto the surface of the circuit board. As inexpensive as this method is, it also requires exposure of the pattern prior to development.
A third application process for the LPI solder resist method is through the use of a photolithography process. This is an advanced method which has the benefit of helping to define or standardise solder mask openings for mounting holes, pads and through-holes.
UV exposure
The LPSM or LPI solder mask application method is sensitive to ultraviolet (UV) light. For this reason, care must be taken when performing exposures.
2. Liquid Epoxy Solder Resists
Also known as liquid epoxy solder resists/masks, they are solder resist types that require an epoxy imprint on the board using a screen printing process.
When working with epoxy resin liquid solder resist inks, the following measures must be observed in order to obtain optimum results:
The process should be carried out using an epoxy resin liquid. It is a thermosetting polymer which hardens when the PCB is subjected to heat curing.
To obtain the best possible colour, the solder mask dye should be mixed into the liquid epoxy.
3. Dry Film Solder Resist
This is also known as dry film solder resist (DFSM). It refers to the process of using a dry film.
Here are some things you need to know about the dry film solder resist process:
Vacuum Lamination Process
Dry solder resist films support the use of a vacuum lamination process. This process supports the application of dry films in the form of solder resist lamination.
Soldering and layering
The completion of the exposure and development process leads to the soldering and delamination process. In this stage, holes are made in the pattern of the PCB. These holes are the channels through which components or parts are soldered to the copper pad.
Delamination is done using an electrochemical process. To work effectively, copper will be layered in the holes and trace areas on the board.
The protection of the copper circuit is enhanced by the application of tin.
Curing process
Before curing begins, the dry film is removed and the etch marks on the copper are exposed. Heat curing is often used to finalise this process.
4. Top and bottom solder resist
This refers to the type of solder resist used to identify or confirm the openings in the green solder resist.
Here are some key points to note about this method:
The solder resist can be placed on the top or bottom of the PCB.
Either the film or epoxy method can be used to pre-add the green solder resist.
Openings registered or created with a mask are used for soldering component pins.
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