First thing that comes to my mind is copper thickness of the through holes.
Extended dwell times will increase the amount of copper etched by the molten 
solder. The amount of etch per second of dwell time will vary from HASL line 
to HASL line. Some vertical lines have a localized turbulent zone which can 
quickly etch the copper plating reducing the overall plating thickness. Most 
horizontal lines have a more even distribution of solder flow. The fabricator 
should have an idea the amount of etch, for a given dwell time, their 
equipment produces.
I am sure there are many other factors, but this one came to mind first for 
me.

Jim Kenny
Merix Corp
503-359-9300


[log in to unmask] Wrote:
| 
| 
| From:  Stephen Ayotte
|        EM Quality Engineering
|        Bldg. 14-3 Col F5 5-1537
| Subject: Fabrication
| 
| Does anybody have any reliability data on the affect of 
| processing
| boards through HASL a number of times, specifically until 
| the board
| material changes color?
| 
| 
| Thanks.
| 
| **** IBM MD Product Quality Engineer       ****
| ****       OEM Quality Engineer            ****
| **** Interenterprise Address: USIB6CEF     ****
| **** Internet Address: [log in to unmask] ****
| 
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