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April 2003

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Subject:
From:
"Crepeau, Phil" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 24 Apr 2003 07:26:15 -0700
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hi,

i agree with this conclusion.  some time back we were getting boards that warped to an hyperbolic paraboloid shape (you know; like a saddle).  burning out the resin showed that warp and fill directions of the glass cloth ran one way in one layer and another in a second layer.  those boards that didn't warp had all warp and fill running in the same direction.  this might explain the sudden increase in warp problems with a vendor. so...burn out the resin in a warped board and count the weave in each direction.  do the same with a non-warped board.

phil

-----Original Message-----
From: Franklin D Asbell [mailto:[log in to unmask]]
Sent: Thursday, April 24, 2003 6:27 AM
To: [log in to unmask]
Subject: Re: [TN] Warped boards


Sounds like to issues...

1) From your board description, with everything being balanced I am assuming
it is a multilayer board, when we see warpage in otherwise balanced layup it
often is cross-weave/ply in the prepreg, if this were the case there is
probably no way to remedy it, other than use as is...somehow...

2) Regarding meeting IPC requirements...the hard approach would be, did you
ask them to meet it? Yes? the you got what you asked for...now learn from
it... If they exceed the specification then you have a strong position...use
it to achieve a better product next time.

Often we recieve purchase order requirements from customers that are boxed,
or generic, and then when a condition may get to the customer they want to
reject for this condition, even though it is well within the "documented
requirements"...so what's a board shop to do...

The problem is often this...designers are sometimes unfamiliar with the IPC
requirements, but place them on drawings nonetheless, buyers are often even
more unfamiliar, and add these additional requirements to the purchase
order, it is only after the boards are received and processed that a company
learns they may have been to lax in some areas...i.e. bow and twist...and
the stuff hits the fan...

Even though the customer orders certain criteria does not necessarily mean
they can use that product (form-fit-function...etc etc) and bow and twist is
a fine example, especially with the tighter and tighter product emerging
(all you spec committess take note) the 1.5% and .75% may not be accurate
with some product...

Bottom line, it is up to the customer to be aware of what they are ordering,
or specifying, to the board shop, it is up to both the customer and board
shop to work towards a consensus on what is achieveable (in fabricating and
assembly) and write product specific specifications or tolerances...because
even if IPC updates the specification, this still will not cover all
eventuality...

In closing, we have also "battled" with customers in regards to warpage;
however, as part of these interesting discussions on meeting
specification -versus- meeting assembly or end use requirements we offer to
assist in revising product specific tolerances as well as give price
reduction, on occasion, for replacement boards in a good faith effort to
help them through this learning opportunity.

...okay, now that I'm behind in my work...I'll let you all ponder that...

Franklin



----- Original Message -----
From: "Grant Emandien" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, April 24, 2003 1:20 AM
Subject: [TN] Warped boards


> T'netters,
>
> On the matter of warped boards we are currently experiencing this problem
> (warpage appears to be in either direction i.e. to the solder or component
> side, sometimes exhibits and S-curve),  - we do not bake these boards to
> remedy but rather reject and return, hence the stand-off with the pcb
> fabricator who is insistent that it is within acceptable IPC stds. PCB
> details are:
>
> *       PCBs are approx. 300mm x 135mm in area,
> *       made of std. Duraver E-Cu 104 (Tg of 135degC) from Isola (no
further
> details),
> *       exhibits relatively good copper balance on both sides, only about
> 20% of the surface  is coppe,.
> *       is only exposed to wave solder heat - it appears that the wave
heat
> may also worsen the problem, so it may appear that stress is already
present
> (on good boards) in the material before wave.
>
> Any experience of this material, what the fabricator's process may be
> inducing and any other possible contributary factors?
>
> Advice graciously received, TIA
> Grant
>
>
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