Agreed the limiting factor is likely to be pad adhesion: did some work in
this area a while ago which indicated you could rework the pads or at least
copper foil same thickness as the pads >8 times, but that in real world
unsupported pads (i.e. no though connection etc) would consistently unstick
after around 4-5 goes. This was very much a pragmatic exercise just to
determine an order of size, too many real world variables with arbitrary
numbers to give a scientific answer. These numbers would be lower now as pad
sizes have decreased

Best regards

Mike Fenner
Applications Engineer, European Operations
Indium Corporation
 T: + 44 1908 580 400
M: + 44 7810 526 317
 F: + 44 1908 580 411
 E: [log in to unmask]
W: www.indium.com
Leadfree: http://Pb-Free.com



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Graham Collins
Sent: Tuesday, October 09, 2001 4:17 PM
To: [log in to unmask]
Subject: Re: [TN] # of rework cycle for SMT gullwing component


Moonman - when I worked for Celestica (Toronto) we only allowed 2 for any
surface finish.  I worked both HASL and OSP.  I believe there was more
concern with pads lifting than intermetallic layer.  Besides - if you have
to replace a part 3 times you have some serious issues to work.

regards

Graham Collins
Process Engineer,
Northrop Grumman
Atlantic Facility of Litton Systems Canada
(902) 873-2000 ext 6215

>>> [log in to unmask] 10/08/01 03:53PM >>>
For fine pitch and BGA, HP and Celestica used to allow two cycles for HASL
(ring a ding) and three for OSP and ENIG. Why is that?

MoonMan

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