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July 2008

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Subject:
From:
Leland Woodall <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Leland Woodall <[log in to unmask]>
Date:
Thu, 31 Jul 2008 15:59:29 -0400
Content-Type:
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text/plain (154 lines)
Good info, Guy.  This gives me something I can submit for consideration
by our executive management staff.

Thanks, everyone, for your help.  I can always depend upon this board to
help me through my week!

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Thursday, July 31, 2008 3:52 PM
To: [log in to unmask]
Subject: Re: [TN] Repair Need for Inverted Chip Resistors

The IPC standards committees had long discussions on this topic. A group
was
tasked to evaluate your concerns and others, like vertical versus
horizontal
alignment of the plates in multilayer ceramic capacitors. 

No manufacturer voiced concern over reliability or performance of either
resistors or capacitors. One member attempted the quantify the
performance
of capacitors in RF applications and found no difference. The committee
voted to relax the workmanship requirements in response. 

Since that time, I used a thin film precision resistor where the maker
recommend mounting with the resistive element down. I asked about this
and
the response was "it provides and measure of protection for the thin
resistive element."

  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Thursday, July 31, 2008 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] Repair Need for Inverted Chip Resistors

Dewey and others,

I've been told the concern lies with the resistive element being on top
of
the component.  With it being mounted upside down, the hottest portion
of
the part when under power is in direct contact with the board.  Would
this
lead to shortened life or cause any type of a premature failure?

Are we being over-cautious about this, or is there some truth to what
I'm
being told?

Leland

-----Original Message-----
From: Whittaker, Dewey (EHCOE) [mailto:[log in to unmask]]
Sent: Thursday, July 31, 2008 2:00 PM
To: TechNet E-Mail Forum; Leland Woodall
Subject: RE: [TN] Repair Need for Inverted Chip Resistors

I'll try to be discreet. If there is no functional impact, then a "let
the
chips fall where they may" approach is acceptable. If the part markings
are
not visible or the vision recognition algorithm of an AOI machine is
impaired, then they may be a problem.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Thursday, July 31, 2008 10:12 AM
To: [log in to unmask]
Subject: [TN] Repair Need for Inverted Chip Resistors

TechPros,

Can anyone tell me if there's a reliability concern with allowing chip
resistors to be mounted upside down?  Our current policy requires that
we
repair these, and I feel that to be unnecessary.

IPC-A-610D shows this to be an acceptable condition on all classes of
product, and our customer has no specific contractual requirement.

I'd like to try to change this policy at our facility, and welcome any
commentary you might have on the subject.

Thanks in advance for your help,

Leland Woodall

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