Ian:
Try cross-sectioning one of the devices and identifying the fracture
nucleation and nature. John Maxwell and Dean Beckley at AVX have
published several excellent industry papers (available from your local
AVX sales rep) on the nature of these.
Thermal (tensile fracturing) board depanelization (stress-strain
fracturing), and board bed/design orientation (compression fracturing)
all have different artifacts and relational causes.
It sounds like you may just want to change dielectric types if only a
few are fracturing (as opposed to a 80% kind of number), and if the
design allows for a widening of tolerances. The reason I say this is the
porosity of the ceramic varies with the dielectric processing; generally
speaking, the more porous ceramics require higher levels of energies to
cause them to fail from mechanical means (fracturing). The down side is
they generally have very wide tolerances and once a fracture has
initiated, it takes less mechanical or electrical energy to metastacize
the failure.
> Bill Davis, Ph.D.
> Diamond Multimedia Systems
> Senior Scientist
> Tel. 408.325.7868
> Cell. 408.888.5650
> e-mail: [log in to unmask]
>
>
>
>
> -----Original Message-----
> From: Ian Squires [SMTP:[log in to unmask]]
> Sent: Tuesday, November 03, 1998 10:35 AM
> 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
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