The Impact of Soldermask Processing on ENIG/ENEPIG Deposit Quality

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Soldermask (SM) is a permanent insulating coating designed to protect the PCB. The mask creates a barrier to contamination, corrosion and handling defects, and it also prevents solder bridging during assembly. The most common type in use today is a liquid photoimageable soldermask (LPISM). The successful application of SM involves multiple processing steps; following vendor recommendations and proper process control could preclude many problems downstream.

The ENIG/ENEPIG deposition also involves multiple processing steps that require the same attention to detail. For best results and the highest solder joint reliability, the product coming to the ENIG/ENEPIG line must have uncontaminated clean copper on which to plate, with perfectly defined and cured SM.

LPISM processing involves the following process steps:

• Surface pre-treatment;
• Application of LIPSM to PCB;.
• Evaporation of solvent (tack dry);
• UV photo exposure (imaging);
• Development of exposed board; and
• Thermal final cure.

Process control of the different steps involved in SM applications is paramount to the success of the ENIG/ENEPIG deposit. Out-of-control processing could lead to skip plating, and/or nickel corrosion; the former results in failure to deliver the desired nickel thickness and the later leads to problems with soldering and solder joint reliability.

The following is a discussion of each process step and its impact on the quality of the ENIG/ENEPIG deposit.Read the full column here.Editor's Note: This column was originally published in the July 20136 issue of The PCB Magazine.