I would consider getting some more quotes and engineering input.
Tombstoning is an indicator of the production techniques, more than layout.
However, his statement isn't totally incorrect and if there was no reason for
having heavy tracks on one end then it would be better to have smaller,
even ones.

To get a tombstone, you need to have the solder melt or wet only one end
of a part and not the other. That indicates either a difference in temperature
(too fast through the oven) or poor paste quality and/or application.

When you consider that the whole PCB (parts, pads, tracks, paste) is going
through the oven, how can a pad be at a different temperature and bleed off
heat ?

Steve.

===========================================

On 3 Mar 2004 at 11:24, Damien Cahill wrote:

> Hi List,
>
> I recently sent away a surface mount PCB for manufacturing quotation.
> The head engineer there sent it back saying I shouldn't run large
> tracks through chip capacitor pads as they will suck away heat and
> lead to component tombstoning.  My problem however is that the large
> tracks I am referring to are microstrip lines carrying RF signals.
> The thickness was calculated to give a 50 ohm impedance to the
> frequencies of interest.  Can I just neck down these tracks at the
> pads to avoid the potential problems identified by the manufacturer or
> will this significantly alter the transmission line impedance?  Has
> anyone come across this problem before and even better can anyone
> suggest a solution.  Thanks in advance.
>
> Regards,
> Damien Cahill.
>
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==========================================
Steve Baldwin                          Electronic Product Design
TLA Microsystems Ltd             Microcontroller Specialists
PO Box 15-680, New Lynn                http://www.tla.co.nz
Auckland, New Zealand                     ph  +64 9 820-2221
email: steve@tla.co.nz                      fax +64 9 820-1929
=========================================

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