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April 2005

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dehoyos, Ramon
Date:
Mon, 25 Apr 2005 09:14:39 -0400
Content-Type:
text/plain
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        Some people are still inspecting to mil specs and see the J Stds as weak and troublesome. There are defects and there are process indicators.  A process indicator tells that a process or training needs to be looked at and perhaps adjusted or changed and do not need to be reworked. Concentrate on the real important problems, such as missings, shorts and so on.
        Regards,
        Ramon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ofer Cohen
Sent: Monday, April 25, 2005 8:16 AM
To: [log in to unmask]
Subject: Re: [TN] Inspection and touch-up of visual defects


Daan,
On one hand, I think that the visual inspection is important. Our
process calls for 100% inspection during the touch up, then two
different stages of sampling with AQL=1%.

On the other hand, I am fighting my QC and touch operators on a daily
basis to avoid unnecessary repairs. 

Meaning: I want to know what is the process quality, but not necessarily
to repair it.

Regards
Ofer Cohen
Manager
Quality Assurance, Reliability and Production Technologies
Seabridge Ltd. - A Siemens Company
Siemens COM FN A SB TQM


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Daan Terstegge
Sent: Monday, April 25, 2005 12:22 PM
To: [log in to unmask]
Subject: [TN] Inspection and touch-up of visual defects

Hi Technet,

I have a question about inspection, touch-up, and how far you need to
go to get a product that meets the required IPC-spec.
According to some reports (i.e. "New Study Reveals Component Defect
Levels" by Stig Oresjo of Agilent) the average defect level in PCB
assembly is around 1100 dpmo. Even with much better dpmo-figures it is
easy to see that except for very simple boards almost every one of them
will have one or more defects before touch-up. A significant portion of
these defects will be visual defects like an isolated spot of flux
residue, overhang of an occasional bent lead, micro-solderballs, an
occasional insufficient solder, an overlooked spike from handsoldering,
etcetera. Although these are all actual defects according to
IPC-A-610,the chance that they will cause the product to fail during
their service-life is minimal.

Now the point of this posting is: how much effort do you need to put
into finding and correcting visual defects.

You could argue that every board that still has a visual defect simply
does not meet the IPC-requirement, and therefore every boards needs to
be 100% visually inspected until you can be sure that you have found and
reworked all visual defects. Subsequent to the 100% touch-up inspection,
another 100% inspection by quality control might be needed to achieve
this. The result is a nice-looking product which meets all the
inspection requirements of IPC-A-610, but unfortunately it will be an
expensive board.
Another approach is to visually inspect the boards mainly for the
purpose of feedback to the assembly process (on sample basis), and rely
on electrical tests for finding defects to be reworked. Quick and
effective, but only some of the visual defects will be found and thus,
formally, the product (or at least some of them) will not meet the
inspection requirements of IPC-A-610.

I try to convince others that we spend more time on inspecting than we
should, but so far every visual defect that is found is seen as proof
that I am wrong. I am interested to hear how others are coping with this
issue.

Best Regards,

Daan Terstegge
Production Engineering
Thales Land&Joint Systems

Tel:     +31(0)35 524 8297
Fax:    +31(0)35 524 8181
Unclassified Email

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