Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


CuOSP and IMM Silver versus HASL

mike weekes

#3129

CuOSP and IMM Silver versus HASL | 31 August, 2000

We are considering alternative Board Finishes to our existing HASL process. The HASL effects opens on 25 and 20 mil packages after reflow and we know if the advantages of CuOSP and other alternatives.

OUR Concern:

Is there a shelf life and handling issue with CuOSP and others? Can you estimate the life of a CuOSP board, as compared to HASL? Any tests you would recommend as part of validation the new finish? Do you take any special precautions in handling the boards on the floor? Do you use either? Can you take a few moments to share your experience? We'd like to switch over to CuOSP and/or immersion silver, but we want to identify and address and NEW Risks these finished present. Can you help?

thanks, Mike Weekes

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Brian W.

#3130

Re: CuOSP and IMM Silver versus HASL | 31 August, 2000

Our customers use OSP, HASL, immersion tin and immersion gold as board finishes. If I recommend a finish to the customer, it is one of the immersion finishes or OSP. Those finishes have the advantage of a flat surface to deposit paste. HASL has variation between pads and on pads, resulting in problems, especially if you micro-reduce your fine pitch apertures. The HASL process usually has a low Cp/Cpk as a process at board houses. Using an OSP, you want to follow good handling procures; ie, do not touch solderable surfaces with your bare hands. Wear gloves or finger cots. You have 3-5 heat cycles, depending on the OSP. I have not had a problem with shelf life, but we have a high inventory turn. Some folks I know store boards for several months and have hadd no problem with OSP. My experience has also been that OSP is usually cheaper than HASL. With the immersion finises, you may have to adjust your profiles slightly.

I much prefer immersion finises or OSP when doing fine pitch. I get a more consistent paste volume, and less problem with lead coplanarity. I have solder defects back to the HASL plating (causing coplanarity issues, poor paste deposistion, etc).

Hope this helps, Brian

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#3131

Re: CuOSP and IMM Silver versus HASL | 31 August, 2000

From the SMTnet Library try: http://www.merix.com/resourcecntr/papers/osp.doc http://www.merix.com/resourcecntr/papers/hasl_alt.doc http://www.itm-smt.com/articles.html * "Organic Solderability Preservatives" * "OSPs - Better Living Through Modern Chemistry"

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