SIPAD Soldermask Recommendations
The design and application of the soldermask coating on a SIPAD board is critical. Without the proper soldermask application, it may be impossible to process certain printed circuits with SIPAD ssd.
There are 2 soldermask recommendations:
- Isolate each smd pad within the footprint. Soldermask dams between pads.
- Isolate all holes from smd pads including via holes as well as component holes.
Tooling Hole Requirements
Soldermask Design, Isolating smd pads
It is very important that the soldermask completely isolate every surface mount land from other smd pads as well as through holes and vias. There should be a soldermask dam between pads even at .4mm (.0157) pitch components. These dams should be well registered and strong.
Click photo for a larger view.
• Soldermask design does not provide dams between smd pads
• Broken soldermask dams can be worse than missing dams
Soldermask Design, Isolating holes from smd pads
• Holes open to surface mount pads can rob solder from smd.
• BGA's require solder mask touch up before processing.
The soldermask on SIPAD boards is the same a standard technology boards. When via holes
are tented, the mask cannot be applied so thick as to create an off contact printing situation.
This can result in scrap, rework, or additional stencils.
Potential Processing Problems
• Damaged pads, shop debris, and soldermask debris can lead to rejects.
Surface Finish Issues - Solderabilty
The SIPAD ssd process depends on a good solderable surface finish from the printed circuit board vendor. Because the SIPAD board is reflowed without components it is very easy to see if the surface finish is wetting to the solder paste. If the surface finish is contaminated or not properly applied the SIPAD ssd finish will not be successful. Potential surface finish issues are listed below.
• Poor HASL Finish.
• Solder paste will not wet properly to HASL finish.
• Flattened SIPAD ssd's will not wet to contaminated HASL finish.
Excess Solder in Via Holes, Nodules
Excess solder in via holes can create an issue during SIPAD processing. Solder in via holes can flow out during flattening creating a solder deposit that could cause quality issues after final assembly. Nodules can also cause printing issues, preventing the stencil from forming a gasket during the printing process.
• Solder in via holes can flow out to cause quality issues.
• Nodules will cause printing problems.
Packing and Shipping
• Warp and twist creates scrap.
• Boards should be packed properly for transport to SIPAD Systems as well as the end user.
• Eraser debris on boards from manufacturing