In a message dated 03/26/97 6:36:10 PM, you wrote:

> Back in January I saw your informative message on the TechNet 
>     regarding the soldering issues w/alloy 42.  I archived it for future 
>     reference, and had occasion to pull it out today, since we're having 
>     some difficulties soldering an alloy 42 component (a 10BASE-T part 
>     made in China).  
>     
>     My question is this...what is the manufacturer's advantage in using 
>     this alloy?  From a contract assembler's perspective, it seems to have 
>     little to recommend it.  Profiles must increased, inspection stepped 
>     up, etc.
>     
>     I suppose that it must be cheaper than a standard tin dipped copper 
>     lead, but is that all there is to it?  Is the use of this alloy 
>     decreasing with time, remaining about the same, or increasing?
>     
>     
>                                                    Bruce Tostevin
>                                           Lockheed Commercial Electronics

Hi Bruce, 
The reason some component manufacturers use Alloy 42 as a lead frame material
is because it makes the attachment of the die easier. The die has a CTE of
about 2.8 and the Alloy 42 has a CTE of about 4.5; so die attach is easily
accomplished with a thin rigid adhesive. Using a copper aloy lead frame
requires a thicker more compliant adhesive to prevent die cracking.
Alloy 42 is more difficult to solder to than copper; however, there is Alloy
42-- apparently coming from a South Korean mill--that is not solderable no
matter what you do. HP ran into this material, and went public with their
experience, as have others who chose not to publisize their experience. I do
not know which mill produces this non-solderable Alloy 42, nor do i know
whether the non-solderability comes in batches or affects all their output. 
The published experience of HP (Engelmaier, W., and B. Fuentes, "Alloy 42: A
Material to be Avoided for Surface Mount Solder Component Leads and Lead
Frames," Proc. Surface Mount International Conf., San Jose, CA, August-Septemb
er 1994, pp. 644-655; also in Proc. Int. Electronics Packaging Conf. (IEPS),
Atlanta, September 1994, pp. 503-516; also in Proc. 19th Ann. Electronics
Manufacturing Sem., Naval Air Warfare Center, China Lake, CA, February 1995,
pp. 5-20; also in Proc. NEPCON West '95, Anaheim, CA, February-March 1995,
pp. 385-395; also in Soldering & Surface Mount Technology, No. 21, October
1995, pp. 20-25) has put some pressure on component manufacturers to change
to copper-based leadframes, but not enough pressure.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************