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

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OSP and SIR | 21 August, 2002

We are using OSP coated boards and no-clean solder paste. In a few instances, we are seeing increased distortion in an audio circuit. Has anybody seen or heard of surface insulation resistance (SIR) decreasing after reflow on OSP boards? Is it possible that the remnants of the OSP are combining with the flux residue and changing the flux residue SIR characteristic?

Thanks for responses.


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OSP and SIR | 21 August, 2002

Splitting hairs, I expect SIR of all solderability protection, including OSP, to decrease after reflow. What�s more, I expect the SIR of all solderability protection to pretty much decrease over time.

The �comb pattern� test specimens meet requirements concerning surface insulation resistance ANSI/J-STD-004 after 96 h and 168 h conditioning in the humidity chamber SIR value is at least 100 MW. log Surface Insulation Resistance (SIR) ||Conditioning time in humidity chamber [hour] ||0||24||48||72||96||168 Cu any coating||12.0||11.2||11.3||11.3||11.0||11.0 Sn-Pb HASL||11.4||11.3||10.5||10.2||10.2||10.3 Electroless Ni /Immersion Au||11.9||11.0||11.2||11.2||11.4||11.4 Electroless Sn OrmeconTM CSN||10.4||9.7||10.7||10.7||10.5||10.1 OSP EnthoneTM Entek Plus||12.0||10.4||10.7||11.2||11.0||10.8 [�Lead - Free Solderability Preservative Coatings of PCBs� Zofia Morawska, Grazyna Koziol, Tele & Radio Research Institute, 03-450 Warsaw, Poland, phone (48-22) 619 22 41 X 263, fax (48-22) 619 25 10; IMAPS Advancing Microelectronics, Volume 28, No. 3, May/June 2001]

Given that it does decrease, it still is within specification [final insulation resistance greater than 5 x 10^8]. So, a straight-up decrease in SIR might not be the angle to take on this problem.

What�s your thinking about: * In-bound res on boards and parts? * Heavy handed application of yer NC? * That, er maybe it�s not so NC?

Or you could get a bit more specific, maybe?

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OSP and SIR | 21 August, 2002

Splitting hairs is putting it mildly. I�m just trying to rule out all variables. It doesn�t appear that we have an SIR problem, but since the newest variable is OSP (blame the new guy for all the problems), I have to consider it.

I�ve seen this before and it usually goes away after the rework techs go home and have a good night sleep.

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OSP and SIR | 22 August, 2002

Did the techs have a restful night?

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