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Wetting Issues - Humidity Related

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Wetting Issues - Humidity Related | 9 May, 2011

Hi, We have been struggling with an issue of non wetting on a QFP (Renesas - 256, Sn90Pb10) but the issue "desapears" sometimes for a while and then back again suddenly. This is the scenario:

Component: QFP 256 / Renesas / Sn90Pb10 / 0.5 mm pitch

Solder paste: Indium NC-SMQ92J Sn63Pb37 / Proflow Cassette

Profile Used: Ramp To Spike - N2 environment.

PCB: HASL finish, 3 ounces copper.

Same component is placed in a different PCB without having this issue, both PCBs are from the same MFG house and both HASL but the other is 2 Oz copper, Both assys run on the same line.

We have been playin with reflow profile on peak temperature, TAL, initial ramp with no success. recently I plotted Defects related to this specific issue with average temperature and relative humidity and there's an evident defect increase when RH increases. Have you seen a sumilar issue before? or how can I contain the it.

thanks in advance!

Ps. Attached are an image of solder profile and defect plot


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Wetting Issues - Humidity Related | 10 May, 2011

Do you have pictures and/or cross-sections of the non-wet? Is the HASL SnPb or SN100?

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Wetting Issues - Humidity Related | 10 May, 2011

From your graph, we just don't see the the relationship between failures and relative humidity. Questions are: * What is the correlation between failures and RH? [We'd bet that the correlation between failures/RH and failures/temperature are 'similar.'] * What is the connection between the two reflow oven thermal runs and the failure rate charting?

Further, RH is a flawed measure. We prefer dew point. For more, look here:

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