Hi Charming,

Two points:

1. The extra thermal excursion at lead free reflow temperatures is a
reliability concern. It is one more thermal cycle that is degrading the
dielectric and the copper. I have seen one extra lead free thermal cycle
have a significant influence on reliability. The quality of fabrication
including copper quality (thickness, distribution etc.), dielectric
robustness and design influences, like grid size, all conspire to
establish the reliability in lead free applications.  

2. A nickel finish usually extends reliability by protecting the PTH
from producing significant barrel crack. So expect the reliability of
the PTH to be reduced by not having nickel protection.

The most conservative approach is to do thermal cycle testing to confirm
or refute reliability of you product in your application.

Sincerely,

Paul Reid

Program Coordinator

PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1

613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Charming Chan
Sent: Monday, November 03, 2008 10:45 PM
To: [log in to unmask]
Subject: [TN] Build backplane with lead free HASL surface finish?

Hello TechNet experts, 

On our master fabrication drawing, the surface finish for backplane is
specified as ENIG, but the fabrication shop ask for waiver to build with
lead free HASL. Is it reliable enough? Any other concerns should be
taken into consideration? Thanks a lot.

Best Regards
Charming Chan
PCBA Engineer

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