Hi Nicholas,
In order for a circuit trace with a nick to completely fracture during IR 
reflow or wave soldering, the nick has to be very severe (=>50% of trace 
width) and you have to have a very resin-rich MLB. However, if the nick is 
close to the PTH barrel, full fracture occurs easier because of the thermal 
expansion of the resin around the PTH barrel during soldering. If you get 
full fracture it is best to do the E-test after your soldering operations 
with the MLB at some elevated temperature; at room temperature the fracture 
surfaces are likely to touch and the E-test will not show anything. 
"Dish down", actually rotating of the land (land rotation) outwards from the 
MLB, results from very high thermal expansion loads during the thermal 
expansion of the resin in the MLB. You get more land rotation with thicker 
MLBs and larger PTH diameters with thick Cu plating ion the PTH barrel.
I give workshops on this subject matter— the next at IPC Expo 2000.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################