|Ask the Experts|
June 18, 2021
Recommended Fiducial Shape
I have tried a "donut" shape but the fab house still has low but significant fall-out.
|Expert Panel Responses|
This defect is not the result of the fiducial shape. All fiducial designs work fine with a normal HASL process. This looks like a touch mark prior to solder solidification.
S T and S Testing and Analysis
What type of equipment is rejecting this as a fiducial? Possibly a plus symbol (+) would work if your equipment will accept.
Director of Corporate Quality Assurance
Delta Group Electronics Inc.
The IPC SMEMA design standard for fiducial marks is a solid filled circle. Ge the standard from IPC.
North America Sales Manager
I recommend using a full circle instead of the donut.
Senior Manufacturing Engineer
In making some assumptions about your board design.... we can only speculate from this photo/question.
The PCB should not be "pooling" solder on the fiducial (or anywhere), this is a PCB house related issue and usually occurs with low cost pattern plating. That said, your board should be checked for cleanliness and if it's more than a Class 2 board this could be a long term problem for the product.
In most PCBA Designs, I would allow LPI solder mask over the fiducial mark. Our camera's were capable of seeing the image with Soldermask over the top of the fiducial. Soldermask is less reflective, and would ensure my camera lighting etc was more robust.
You may try masking over fiducial mark, to avoid variation of HASL on the pad. They call it HASL for a reason.
Capital Equipment Operations Manager
Specialty Coating Systems
The HASL process tends to create thicker "bumps" of solder on small pads and thinner more flat deposits on large pads. Decreasing the copper area of the fiducials from a circle to a donut might have aggravated the issue, creating larger bumps.
We suggest increasing the size / copper area of the fiducials if possible. Then the HASL process might be able to blow the solder a little more flat in that area.
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