Werner
Have you written a TM on this Chisel/Screwdriver test???
:-))
Seriously, I've seen better results with extended reflow times (not
necessarily higher temperature) for Palladium finish components for many of
the same reasons you mention.
Best Regards, Mel
Mel Parrish
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier
Sent: Tuesday, May 13, 2003 11:37 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG reflow profile vs HASL
Hi,
Part of the confusion results from sloppy language.
(1) the settings of reflow machines are reflow soldering recipes, not reflow
soldering profiles. Different reflow soldering profiles will result from the
same recipe at different locations on an PCA and will depend on the thermal
masses and access of the heat transfer media involved.
(2) solder "wetting" is not just getting the solder liquid and touching the
surface to be "wetted;" wetting includes all of that, but also the
dissolution of the base metal [different base metals require rather
different
amounts of heat because of thier wastly different dissolution rates in tin]
to form intermetallic compounds (IMCs) which give you the desired
metallurgical bond.
Chris,
ENIG boards require higher temperatures than HASL boards.
When you solder to a HASL PCA, you are soldering to an already existing
solder joint with the IMC in place and all you have to do is melt the solder
volumes. Given todays reflow machines and belt speeds, the peak reflow
temperature for the slowest heating solder joint should be Liquidus
temperature for the solder used plus 20°C [thus, for 63Sn/37Pb the minimum
peak reflow temperature is 203°C and should be held for about 5 sec to
assure
consistent high quality solder joints to copper with OSP.
When soldering to nickel, you need Liquidus temperature for the solder used
plus 35 to 40°C [thus, for 63Sn/37Pb the minimum peak reflow temperature is
218 to 223°C, because Ni dissolves so much slower in Sn than Cu. You can
easily test whether you have achieved proper solder joints--prying a solder
component off [chisel or screw driver test], will result in the soldering
pads coming off the PCB or component or the SJs fractuing in the solder
volume for stress-concentration geometries. If the separation results in the
solder and the soldering pads separating at the interface, no metallurgical
bond has been formed either because of insufficient heat or sme
solderability
deficiency.
The Au on the Ni protects the underlying Ni from oxydation, and actually
promotes a slightly faster spreading of the liquid solder over the Ni
surface
because of the high dissolution rate of Au in Sn.
Mike's advice makes practical sense; it presupposes that you actually
measure
solder reflow profiles --as you should so you know what they really are.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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