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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Contamination

Views: 2345

T. Oaks

#43279

Contamination | 11 August, 2006

Hi, We have a issue with current leakage between pins on an SSOP 28 in a low frequency RF application and there is a suspicion that it is being caused by something in the flux residue. We have had the bad boards analyzed and a 'high' Chloride level was found. Does anyone have some data on what level causes what type of issues? I can see the chloride causing long term problems but not immediate leakage problems. Any info on studies or experience with this type of problem would be appreciated.

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#43285

Contamination | 13 August, 2006

ANSI-J-STD-001, MIL-P-28809, MIL-STD-2000: LT 10.07 �gm/in^2 NaCl equivalent

Electrochemical failures are the result of contaminants residing on the surface of the laminate and/or components of an assembly. To create the reverse plating cell that produces electromigration, required components are: * Bias voltage * Moisture * Active ionic material.

For more reading, Google => electrochemical migration

What flux are you using?

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T. Oaks

#43329

Contamination | 15 August, 2006

We are using Alpha UP78, which has generally good SIR values. We are seeing current jump from around 6 micro amps to 60 micro amps in a very small percentage. This does not seem to be likely with just ions immediately after reflow. The current would revert to normal after cleaning with IPA. Any thoughts on this?

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#43349

Contamination | 15 August, 2006

Alpha UP78 was a modern solder paste. Check with your supplier for recommendations.

You're are cleaning some flux residue with the IPA and reducing the leakage current.

We're not wild about using IPA. Problems with IPA are: * IPA / material being 'cleaned' combination still needs to be removed from the board. * IPA and empty containers are a hazardous material by RCRA criteria (40CFR 261) * Flash point (~12*C TCC) of IPA is low enough that all electrical equipment within a couple yards of the bath must be flameproofed or intrinsically safe to prevent a fire. * IPA is harmful to people, requiring personal protective equipment including: skin protection [chemical resistant glove, not some pourous butt examination gloves], eye & face protection, and respiratory protection. * IPA is a volatile organic compound (VOC) that forms ozone when mixed with Nox, primarily from automobile exhaust, on warm, sunny days.

Look here: http://www.tsi.com/documents/1080546d.pdf

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blnorman

#43510

Contamination | 23 August, 2006

We have seen leakage currents around parts that have high impedance. Evidently with a small amount of moisture, weak organic acids present in the flux residue can cause a low leakage.

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Non-heated dispensing system

SMT in-printer dispensing