Solder Mask is a mixture of chemicals that prevent molten solder from running over the areas that have been cured with Solder Mask.
The Solder Mask is made up of two components that are used in a 1-5 ratio depending on what colour and type you are using. The 1st component is the paste, which is the main part of the mixture, this comprises of the pigment and the chemical properties that resist the solder. The smaller 1/5th part is the hardener which is combined with the paste, to enable the Solder Mask to be cured by heat or UV processes.
The normal and most commonly recognised colour for PCBs is green. The green colour is given to the PCB by the Solder Mask. The popularity of the colour green is the result of a number of factors but the two main ones are as follows:
- Inspection: It is widely accepted that any manufacturing imperfections will be spotted more easily by the human eye if presented against the colour green. Following this discovery it has become the colour of choice although many engineers and designers will specify this as habit without the understanding of the true reason behind their selection.
- Processing: not only is it quicker and more efficient to produce and use green Solder Mask but it is also considered the most affordable. This is purely due to the fact that most PCB suppliers stock green in large quantities bringing the overall price of the ink down dramatically.
Recent Developments in PCB manufacture technology have resulted in the need for a new type of Solder Mask and consequently there are now two different types of generic ink available on the market. Firstly the standard Solder Mask as described above, and now a new standard of LED White Solder Mask. The key driver for the introduction of this type of mask has been the growing popularity of LED lighting. The key difference between the inks can be found in their reflective properties. The LED White ink is used to enhance the brightness of the LED’s due to a reflective background dispersing more light. Additionally the ink does not lose its bright white surface after heat treatment – something which is crucial for LED manufacturers.
Some Manufacturing Notes:
Typically a standard pot of ink is measured in 1kg increments; each kilogram will last for approximately 40 manufacturing panels sized 18 inches by 12 inches, depending on what ink is being used. For an LED White based ink 1 kilogramme may only last for as little as 10 manufacturing panels due to the thickness of the ink. Here at Ragworm we have cupboards full of Solder Mask in a rainbow assortment of colours due to the many different customer requirements. We are always on the lookout for new projects that will push the boundaries of what is ‘normal’.