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February 2000

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Subject:
From:
Nancy Trumbull <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 3 Feb 2000 08:53:50 -0500
Content-Type:
text/plain
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text/plain (235 lines)
Rick,
"Thanks for letting me know I was wrong.
I think the mistake was a good one for me because look at all the information I have gotten.  So let me say that I'm sorry for miss reading your mail. Then say thanks to all the netters for the very informative replies.
May I say that I talk about the technet  to others here and how if I need information I know where I can get it.  
We are the lucky ones.
Well I don't what any netters head to exploded.
I'm sure I well need to pick  their mines later.
Have a Great Day and I hope you got your answer.
I'm sure I've upset some with my apology.
So before you get started I'm going to say 
S   O  R  R   Y 
Nancy T.
>>> "Howieson, Rick" <[log in to unmask]> 02/02/00 01:35PM >>>
Nancy,
Sorry I was not clear. Measling prior to assembly (bare board).
Rick

>-----Original Message-----
>From:  Nancy Trumbull [SMTP:[log in to unmask]] 
>Sent:  Wednesday, February 02, 2000 7:41 AM
>To:    [log in to unmask] 
>Subject:       Re: [TN] Measling
>
>Hi Again,
>  I wish to be enlightened.  My understanding of the original problem was
>measling during  hand soldering process.  Sorry if I read it wrong and took
>off on  soldering process.
>
>All that I have been reading sounds right and about the same.
>Therefore I agree with just about everyone.
>But now All of you have me wondering.
>So here it is another statement and question from me.
>Statement:
>From past experience MY understanding of PROCESS MEASLING CAN  FROM reflow
>soldering,  hand soldering or any type of thermal induce process.
>
>My understanding has always been that measling as an inherent or assembly
>condition is acceptable.
>
>QUESTION:
>How done  assembly process measling occur.
>
>Oh by the way I want to thank all of you for putting up with me and to let
>you know that I have been a technetter for one year and my knowledge has
>grown greatly.
>I do off and on put in my two cents and love it went you give me back a dime.
> Waiting to hear from any and all.
>Have a great day
>Nancy T.
>
>>>> Brian Ellis <[log in to unmask]> 02/02/00 06:58AM >>>
>Kelly,
>
>I'm 100% with you on this. Measling is due essentially to too little resin at
>the fibre
>"bumps", because either it was squeezed out too much during pressing or there
>has been
>a chemical attack of the resin, baring the fibres. The real problem with real
>measles
>is that chemicals can enter the fibre structure by capillary action, after
>which
>anything can (and does) happen. Overheating pads is not a cause for measles
>but, sure
>as God made little green apples, it can cause one helluva lot of other
>problems. This
>is why we put thermal breaks in ground and power planes, just to reduce this
>risk.
>
>Brian
>
>"Kelly M. Schriver" wrote:
>
>> Whoops!!  Help me with this one, guys!!   Measling, by definition, occurs
>> only at the intersection of two fiber bundles within the lamina.
>> Accordingly, it cannot occur in the same plane as the metal foil of that
>> laminate layer.   The size of a measle is self limiting by the structure of
>> the glass (or fiber) bundles.  Further, one measle cannot join with an
>> adjacent measle or become a running fault in the laminate.
>>
>> Crazing and delamination, however, can occur in the same plane as the metal
>> foil, and can become large running or bridging faults.  I've seen numerous
>> cases of crazing which were misdiagnosed as measling.
>>
>> Many of the publications, such as WS6536, MIL-STD-2000 and others failed to
>> recognize this charactaristic about measles vs other internal laminate
>> faults, leading to a few misconceptions.  I have seen no indication of test
>> data, other than some specialized high power applications which suggests
>> that real bona fide measles are a reliability problem.
>>
>> Regards - Kelly
>>
>> -----Original Message-----
>> From: rampinc <[log in to unmask]>
>> To: [log in to unmask] <[log in to unmask]>
>> Date: Tuesday, February 01, 2000 6:39 PM
>> Subject: Re: [TN] Measling
>>
>> >Rick,
>> >
>> >Be careful. Measling can be a source of reliability problem when it
>>bridges
>> two
>> >conductors. Measling becomes 'A' type defect ( Critical function -causing
>> rejection)
>> >when two conductors of different polarity are bridges. If glass fibers
>> become visible
>> >in a measled spot, that is also a cause for concern.
>> >
>> >Send  pictures of measled board for further discussion if you like.
>> >
>> >"Howieson, Rick" wrote:
>> >
>> >> IPC states measling is not cause for rejection. Anyone out there know
>> >> where I can get supporting data that documents testing performed to come
>> >> to this conclusion? All help is appreciated.
>> >>
>> >> Rick Howieson
>> >> http://www.gt-corp.com 
>> >>
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