This question deliberately used the term ‘costs’, in order that you should consider process complexity, material cost and yield. On all three counts, the tighter the tolerance, the smaller the clearance between solder mask and underlying tracks and pads, and the more expensive the solution will be. For example, using pocket solder mask windows will automatically rule out the cheap screen printing option.
The criticality of dimensions will also affect the quality of the assembly – the solder mask needs to cover conductors under the solder resist, without interfering in any way with pads or fiducials.
The design will affect the process, and the process will determine the thickness and evenness of the solder mask coat. Excessively thick solder mask can cause problems such as drawbridging.
If tented vias are used, these should be within the guide lines of IPC-2221, otherwise the integrity of the tent may be compromised.
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