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HASL surface finish

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HASL surface finish | 12 June, 2020

Has anyone had an issue with changing from a HASL surface finish to a LF HASL finish if it is still being used in a leaded process?

Also we are having issues with the planarity on the fiducials with the HASL finish. Are there any suggestions or changes to suggest to our board house to help? ENIG Gold is not an option due to the cost and we do not go through our panels fast enough to look at OSP.

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HASL surface finish | 14 June, 2020

We did a batch of boards with lead free HASL that we thought was leaded. Using standard leaded paste worked, but we did have some wetting issues. The issues were resolved when switching back to leaded HASL.

Can't speak to your specific fiducial issue, but HASL is always a pain for our camera compared to ENIG. It's just so uneven in how it reflects light.

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HASL surface finish | 15 June, 2020

You may find some wetting issues running LF HASL with 63/37, as your reflow temperatures will be significantly below the LF reflow.

On fiducials...if you don't have a quote for your boards with ENIG, I would recommend at least checking it out. It's likely to be less expensive than anyone thinks.

If ENIG is still not an option, then, as Kyle mentioned, optical recognition of HASL fids can be a pain due to shadowing. You can try playing with the parameters of the optics to see if you can get a consistent read. One solution I've used in the past, if available, is to read a negative image instead of a positive image (the lighter areas would show up dark on the negative, and might smooth out the inconsistency of the solder on the fid). Finally, you could try sticking a white dot over the fiducial to smooth the edges; but, this can lead to centering issues depending on the accuracy of the person putting down the dot, and the size of components on the board.

Cheers, ..rob

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HASL surface finish | 15 June, 2020

Tin/Lead has 183C melting point and probably around 220 peak temperature at reflow. Tin has 232C melting point. I would assume that based on this information you would understand why intermetallic joint is questionable. Go to any flat finish. HASL will always give you problems in production, because of uneven deposit.

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HASL surface finish | 15 June, 2020

Try sending your boards to rework before SMT and have them remove the excess solder from the fiducials. It usually works great until someone accidentally removes the entire fiducial.

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HASL surface finish | 16 June, 2020

for the fiducials, try a donut shape instead of a disc. The HASL solder seems to settle more evenly on a donut than it does on a dic.

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HASL surface finish | 24 June, 2020

Hi. Taking this from a total different angle - why not use ENIG to avoid this issue but find more competitive suppliers? We source from offshore all the time and finding that due to this dreaded virus - the market pricing is soft. Many are willing to reduce their resales on the ROHS and/or Halogen free PCBs with high quality to win new business. Share the details of how many layers and will post more details on firms we recommend and have used in the past 30+ years of PCB sourcing. Our mix is typically 4L with a few 6L FR4; ENIG in ROHS and Halogen Free (we supply Foxconn and other tier 1 firms who require HF laminate). Now getting into buried and blind vias. Openly, we saw HASL finish one time and did not want it again in our building.

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