Dave:

Marc isn't the only one with questions about the preheat parameters. Can
you spell out where the temperature is measured and how it was
determined that 125°C is the temperature that a component "sees" during
processing? For that matter, what does "sees" mean?

I think Marc's question is very clear. If the solder will melt at 225°C
or more, there's a 100°C delta between preheat and melting temperature.
Why such a huge difference between "preheat" and ultimate reflow
temperature?

Many thanks.

Jim Smith
Cambridge Management Sciences, Inc.
4285 45th St. S.
St. Petersburg, FL 33711-4431
Tel: (727)866-6502 ext. 21
Fax: (727)867-7890
eMail: [log in to unmask]

David Hillman wrote:
> 
> Hi Marc! Our focus group is following the test procedures as prescribed by the
> ANSIJ-STD-020A specification which is the specification the component
> fabricators follow. The 020A spec contains the different conditioning parameters
> which correspond to the different MRT levels (e.g. 1-6) and the reflow profile
> parameters of temperatures/ramp/dwell. The MRT testing is designed to simulate
> the temperature a component "sees" during processing. I am a bit confused on
> your T-difference question - can you please expand on the question.
> 
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
> 
> Dittes Marc <[log in to unmask]> on 04/20/2000 02:51:17 AM
> 
> Please respond to "Leadfree Electronics Assembly E-Mail Forum."
>       <[log in to unmask]>; Please respond to Dittes Marc
>       <[log in to unmask]>
> 
> To:   [log in to unmask]
> cc:
> 
> Subject:  [LF] AW: [LF] DTI update report
> 
>   ------------------------------------------------------------------------
> 
> Hello Dave,
> on of the most important questions on the MSL testing is (beneath the peak
> temperature) that for the temperature for preheating. According to the
> NEMI-proposal on MSL testing for Pb-free solutions the preheat-temperature
> is 125 °C. This doesn´t match the demand for small T-difference on the pcb
> in the peak zone. Hence my question. Do You know anything about the profile
> used in these tests you mentionend?
> 
> Marc Dittes
> 
> -----Ursprüngliche Nachricht-----
> Von: David Hillman [mailto:[log in to unmask]]
> Gesendet am: Donnerstag, 20. April 2000 01:22
> An: [log in to unmask]
> Betreff: Re: [LF] DTI update report
> 
> Hi folks! Just an FYI - there is a group this working on addressing the
> issue of
> lead free component finishes - the Lead Free Component Finishes Focus Group.
> This is a small group of component fabricators and assemblers that have put
> together a "skunkworks" effort to develop some data concerning the following
> issues:
> 
> 1) What happens to current component moisture sensitivity ratings on
> components
> (per IPC-JSTD-020A) if a test temperature of 260 C is used instead of 230C?
> 
> 2) What are the solderability aspects?
> 
> 3) What are the visual quality assessment impact on assembly?
> 
> 4) What is the thermal cycle reliability?
> 
> The group is looking at the following lead finishes: SnPb, PdNi, SnCu, Sn,;
> the
> following pwb finishes: HASL, AuNi, OSP; the following solder alloys: SnPb,
> SnAgCu, SnAg; for both through hole and surface mount technologies. The
> group
> will be presenting their test data at the IPC Fall meeting in September at
> Miami
> Florida as part of D. Fritz's IPC  Alternative Final Finishes committee
> paper
> session.
> 
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
> 
> David Gowlett <[log in to unmask]> on 04/15/2000 05:28:58 AM
> 
> Please respond to [log in to unmask]
> 
> To:   [log in to unmask]
> cc:
> 
> Subject:  Re: [LF] DTI update report
> 
> Hello Mike,
> 
> Thanks for the reply; I still believe that the myths and legends of tin
> whiskers need to be dealt with.
> 
> Many technical papers still claim that whiskers are a serious problem. I
> have read an alarming report from the Department of Health, Education and
> Welfare issued on March 14, 1986 dealing with failure of heart pacemakers
> due to tin whiskers this problem caused a Food and Drug Administration Class
> 1 recall.
> 
> http://www.satellitetoday.com/viaonline/backissues/1998/1098dollars.htm
> 
> The above web site contains details on the failure of satellites which was
> attributed to tin whiskers
> 
> I have read a lot of technical paper about the elimination of tin whiskers.
> They mostly claim that the risk of whiskers can be reduced by reducing the
> organic content of the tin and by not subjecting the plated deposit to
> stress.
> No one has ever stated that whiskers can be eliminated!
> If the plated component is subjected to any forming after plating the
> resulting stress can increase the risk of whiskering, unless this stress is
> removed by either annealing or reflowing the tin. The vast majority of
> components and wires that we plate are subjected to subsequent forming and
> in a lot of cases cannot be reflowed.
> 
> The main problem that exists is that there is no standard test for whiskers
> on tin although I understand that Ms. Kay Nimmo from ITRI is co-ordinating a
> test program, aiming at coming up with a standard method.
> 
> I will not recommend pure tin as a replacement for tin/lead until we can at
> least test the risk. If any of our customers ask for pure tin I will supply
> it but only after making them aware of the risk.
> 
> We need a decision on the risk of whiskers from a Government level.
> 
> Best regards,
> David Gowlett
> Technical Director
> Palmer Plating Ltd
> Cirencester
> England