To begin with, get educated as to what happens when there is no lead alloyed with tin
See http://nepp.nasa.gov/whisker/
And this document
http://www.hlinstruments.com/RoHS_articles/USAF%20AW%20Advisory%20AA-05-01%20Lead-Free%20Solder.pdf
Which states
"NASA's policy states, "Pure tin plating is prohibited as a final finish on EEE parts and associated hardware." NASA Parts Advisories NA-044 and NA-044A address this topic and contain extensive lists of specifications, a large number of which prohibit pure tin; many specify a minimum inclusion of 3% lead content. The Defense Logistics Agency3 has provided a sample list of defense specifications which preclude the use of pure tin: for Monolithic microcircuits, MIL-PRF-38535 Para A.3.5.6.3; Hybrid microcircuits, MIL-PRF-38534 Para E.4.2.7; Semiconductors, MIL-PRF-19500 Para H.4.1; Film resistors, MIL-PRF-55182 Para 3.5.3.4; Chip film resistors, MIL-PRF-55342 Para 3.5.3; Chip tantalum capacitors, MIL-PRF-55365 Para 3.5.2.3; Ceramic capacitors, MIL-PRF-39014 Para 3.5.1.1; and Relays, MIL-PRF-39016 Para 3.4.1.a.4 "
Read this draft statement by the Dept of Defense, 23 Nov 2009
http://www.hlinstruments.com/RoHS_articles/DoD%20Lead%20Free%20Policy%2023%20Nov%2009.doc
MEMORANDUM FOR SECRETARY OF THE ARMY
SECRETARY OF THE NAVY
SECRETARY OF THE AIR FORCE
DEPUTY UNDER SECRETARY OF DEFENSE
(ACQUISITION & TECHNOLOGY)
DEPUTY UNDER SECRETARY OF DEFENSE
(LOGISTICS & MATERIEL READINESS)
DIRECTOR, DEFENSE RESEARCH AND
ENGINEERING
DIRECTORS OF THE DEFENSE AGENCIES
SUBJECT: Policy on Lead-Free Solders and Finishes in Defense Materiel
Many companies are phasing out traditional tin-lead solders and piece part finishes, following the European Union legislation on Restriction of Hazardous Substances, related legislation, and the global shift it instigated. Although excluded from such legislation, military systems are nonetheless affected. As a result, DoD programs are experiencing effects that add risk and cost to the development, acquisition, and sustainment of military electronic systems. Because of the need for safe and reliable systems, some programs have opted to continue using traditional tin-lead solders and finishes. This option is not viable for all DoD programs, particularly those using commercial piece parts and assemblies. Unfortunately, even those systems not allowing any use of lead-free materials are challenged to implement configuration control strategies to ensure that unwanted commercial-off-the-shelf materials are not mixed into the supply chain.
Each Component shall require its systems and programs minimize the effects due to the global transition to lead-free electronics processes and products. Each program, regardless of acquisition category, shall document its lead free control plan and associated risk management activities in its Systems Engineering Plan and Life Cycle Sustainment Plan. A lead free control plan documents processes that assure stakeholders that electronics systems will continue to be reliable, safe, producible, affordable, and supportable. Guidance on this can be found in GEIA-STD-0005-1, Performance Standard for Aerospace and High Performance Electronic Systems Containing Lead-Free Solder and GEIA-HB-0005-1, Program Manager's Handbook for Managing the Transition to Lead-Free Electronics in Aerospace and Military Systems.
My point of contact for this policy is Mr. Nicholas Torelli, Director of Mission Assurance, Office of the Director, Defense Research and Engineering, [log in to unmask]
This document re solder joint reliability of SAC BGAs in tin/lead assembly process
http://www.hlinstruments.com/RoHS_articles/Solder%20Joint%20Reliability%20of%20Pb-free%20Sn-Ag-Cu%20BGA%20in%20SnPb.pdf
This document
http://www.hlinstruments.com/RoHS_articles/Lead%20Free%20Electronics%20Impact%20on%20DoD%20Programs.pdf
This USAF document
http://www.hlinstruments.com/RoHS_articles/USAF%20AA_08_02%20Airwothiness%20Advisory%20Combined.pdf
http://www.hlinstruments.com/RoHS_articles/Solder%20Joint%20Reliability%20of%20Pb-free%20Sn-Ag-Cu%20BGA%20in%20SnPb.pdf
In your spare time read my collection of documents (a small sampling of over 18,000 documemts on the subject0 !
http://www.hlinstruments.com/RoHS_articles/
Were it my product being used in an aerospace or military application, I'd reball the devices with tin/lead and use tin/lead solder to attach all components then coat with a conformal coating after plating any remaining tin with an electroless nickel coating using our patent pending process (currently the only commercially available process to suppress tin whiskers).
FYI, there have been studies done indicating that soldering SCA BGAs with tin/lead solder is not a good idea.
Bob Landman
Managing Partner
LDF Coatings, LLC
www.ldfcoatings.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Poh KH
Sent: Monday, August 27, 2012 10:11 AM
To: [log in to unmask]
Subject: Re: [TN] Leadfree process on Military and Aerospace.
Hi Technetters,
I am wandering if leadfree process is allowed to use on Military and Aerospace product.
Today, most BGAs' spheres or balls are lead free.
If it is required to remove and reball with leaded balls ?
Thanks.
KH Poh
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