In response to previous postings with regards to internal registration, I
have always raised the concern that if breakout is allowed, the resulting
minimum dielectric between the pad with internal breakout and adjascent
conductors is compromised. The concerns that you have raised with regards to
wicking accentuates even further the need to maintain not only internal pad
registration, but also minimum dielectric spacing by design INCLUDING
allowances for wicking. 

An example:
If the product exhibits a 0.005 inch dielectric space by design, assuming a
minimum 0.001 inch of annular ring is maintained, should wicking be present
to a maximum of 0.003 inch, then the resulting dielectric between the
termination of the wicking and the adjascent conductor would be 0.003 inch.
This violates the minimum dielectric for (the now obsolete) IPC-RB-276 para.
3.9.2.6 which states a minimum dielectric of 0.0035 inch EVEN WITH NO PAD
BREAKOUT!

Wicking needs to be assessed in context of the total product characteristics
including, as a minimum, design rules used, internal registration and
customer requirements.

Comments????

Dave Rooke
Circo Craft - Pointe Claire
_________
>I received a call from a member inquiring whether there is any IPC 
>activity taking place on wicking.  With PWB designs becoming increasingly 
>dense, spacings on internal layers can be at risk with minor 
>misregistration and solder wicking.
>
>I know that ITRI is working the registration issue.  Is anyone actively 
>working to study wicking. Looking at:
>
>o  Material differences
>o  Alternate metallization techniques
>o  Different glass styles
>o  Other?
>
>Anything will help.
>
>Best Regards
>
>__________________________________________________
>
>David W. Bergman, V.P. of Technical Programs
>IPC
>2215 Sanders Road
>Northbrook, IL  60062-6135
>847-509-9700 x340 Phone
>847-509-9798 Fax
>email  [log in to unmask]
>www  http://www.ipc.org
>faxback support 800-646-0089
>---------------------------------------------------

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************