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May 2014

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Subject:
From:
Greg Munie <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Greg Munie <[log in to unmask]>
Date:
Fri, 9 May 2014 15:17:07 +0000
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Do you know where the failure is located, e.g. is it a low impedance caused by corrosion products under the QFN? (May be hard to find under the low standoff.)

I have seen something like this before. The "short" was under the QFN. Removing the part, cleaning and replacing the part using a Telecordia approved flux without cleaning the flux residue restored the board functionality.

May not apply here but my 2 cents.

Greg

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rivera, Raye
Sent: Thursday, May 08, 2014 7:04 PM
To: Technet
Subject: [TN] Appropriate coating for mixed gas airborne contaminant test failure?

Hello Technetters,

We are qualifying a new product to telecom standards, and had an unexpected failure during an indoor airborne-contaminant test. The test is 10 days exposure to 10 ppb Chlorine, 10 ppb Hydrogen Sulfide, 200 ppb Nitrogen Dioxide, 200 ppb Sulfur Dioxide.  (Test procedure is from GR-63-CORE  5.5.2.2 and according to ASTM B-827-05-2009.)

One specific component failed, at two out of five placements on the board.  It is a 3 mm x 3 mm  QFN. Both parts still function marginally but with a reduced output voltage that brings down the board. The two locations that failed are directly in the path of the DUT's cooling fan which runs throughout the test. We are still doing the device level failure analysis.

At this early stage, we are considering conformal coating to protect this part. Does anyone have a suggestion for what kind of conformal coating would be appropriate for this mix of corrosive gasses?

This is a bit out of my experience, so I'd appreciate any tips or warnings for a situation like this.


Best regards,
Raye Rivera

QA Manager * Canoga Perkins
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