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November 1998

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Subject:
From:
Paul Klasek <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 4 Nov 1998 08:40:49 +1100
Content-Type:
text/plain
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text/plain (122 lines)
Oups, Ian ; by the sound of it you're in a jam ;
don't get crossed if I see in my crystal ball (one) something what does
not agree with your hard facts :
1)
Somewhere; I think in one of Werner's papers I've read anything less
than 6mm of ceramic on FR4 stands the dilatation's .
That should not be it ; I presume the "problem" is plain crack ; even
without reliability cycling .
2)
Circular cutter ( CAB in V ?) ; or more so still the handling is more
likely ( as you've guessed as well = 0.6 mm end of pad from blade is
highly inconsiderate to the senior cap in question ; I have to say ; you
design fellow likely does not know the blade diagonal stresses in travel
; levered by the size of that thing is sure recipe for crack .
You have my sympathy > hey ; keeps us in job !
3)
The remedy would likely be :
a]
Abandon the circular blade ; it will stress the "design" even if your
operator will feed the panel through on feathers .
Or change the design = move the cap in ; the corner is A brutal place .
b]
If (likely) you can not do anything about design ; than shear ( yes, a
very good guillotine ) will help .
AND feather support ; obviously ;
terrified gentle gender is much more suitable than "confident" handy man
.
May I suggest subsequent use of the French Instrument consequently
utilizing design lad's voluntary cooperation .
c]
break the biscuits PRIOR assembly .



See you Ian


Paul Klasek
colleague on the other side
http://www.resmed.com

> ----------
> From:         Ian Squires[SMTP:[log in to unmask]]
> Sent:         Wednesday, 4 November 1998 5:34
> To:   [log in to unmask]
> Subject:      [TN] 2220 ceramic cap failure
>
> All
> Well here it is! my monthly poser for the forum.
> This is one that has come back to haunt me a little, in my first few
> weeks with my current employer i was asked to look at a Small gating
> circuit with a production 'eye'.
> I was unhappy about several of the design features and said so.....but
> being 'johnny come lately' was largely ignored.
> So....we have a board 28mm x 9mm x 0.9mm, populated both sides with
> 0805's, 0603's, SOT23's and a ceramic cap 2220.
> guess what the problem is??? yep the LARGE cap
>
> Cte mismatch between the ceramic and the FR4 in my opinion is too
> much.....agree/disagree?
> The component has one pad running parallel with the long side of the
> PCB 2mm inboard. The other pad runs parallel with the other long side
> of the PCB....0.6mm inboard.
> The boards (50 to a panel) are populated, reflowed both sides and then
> cut out using a circular cutter.
> Pad distance from edge and likely vibration damage are surely
> wrong...agree/disagree???
> Any other possible problems or areas of note would also be appreciated
> as design are still refusing to accept any of this (assuming i am on
> the right track), hard evidence or IPC related docs would be
> appreciated.
> Meanwhile we have a line stoppage and our subcontractor is being
> blamed for poor manufacture. Anyone want to fight their corner with
> me???
>
>
> Regards
> Ian Squires
> Senior Production Engineer
> -------------------------------------------------------
>
> Graseby Dynamics Ltd
> A Smiths Industries Company
> Park Avenue, Bushey, Watford, Herts, WD2 2BW
> Web Site: www.gradyn.co.uk
> Phone:    01923-228566 xt 295
> Fax:      01923-221361
> E-mail:   [log in to unmask]
>
> Registered in England no. 480992
> Registered office:
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