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April 2006

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Subject:
From:
Andre LeClair <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Andre LeClair <[log in to unmask]>
Date:
Wed, 5 Apr 2006 15:16:00 -0400
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Jim

The circuit actually is from ERG incorporated into our customer's design.
The failure is usually the transformer burning up (over heating) or if a
winding goes open the input transistors blow (smoke fire ect.). Our Test
Eng. is thinking there may be some small leakage across the cap (or PCB).
The backlight is 6mA typical and the driver is also 6mA, so his thinking
that any increase in the load current and the transformer fails. Then the
question was raised about n0-clean potentially contributing to this.

We have only seen a couple boards that had any sign of possible arching at
the cap.  The cap is an 18pf 4000v 5% COG from NovaCap.

I did manage to get a hold of a PCB layout recommendation for the circuit
which suggests a slot between the cap pads and to conformal coat. (The
customer did not do this)



_____________________________
Andre Leclair
Process Engineer
Ansen Corporation
315-393-3325 ext 293
315-393-7638 FAX

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, April 05, 2006 2:28 PM
To: [log in to unmask]; [log in to unmask]
Cc: [log in to unmask]
Subject: Re: [TN] Arching or Current Leakage



Andre,

What is the failure mode of the circuitry - leaky capacitors on the output
of the backlight driver?  What type and voltage rating are the capacitors?
Are there any external signs of the failure mode, ie burn marks,
electro-migration paths, etc?

Jim Carlson
Sr Quality Assurance/Reliability Engineer
Rockwell Collins EW-SIGINT
Phone 443-489-9121
Fax 443-489-9290



Andre Leclair <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>


04/05/2006 02:11 PM


Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Andre Leclair <[log in to unmask]>



To
[log in to unmask]

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Subject
[TN] Arching or Current Leakage






We have a customer that has a portion of a circuit which randomly fails.
The circuit is a backlight driver (500volt 6mA). The output caps are 0.100
spacing of the terminals.  The process used is No-clean.  Can the No-clean
contribute to failures of the circuit (ie promote arching or current
leakage across the body of the output caps). ???

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