Gold embrittlement is well understood, but not widely understood. The good news is, the risk of gold embrittlement has been quantified. It is a function of the solder density and the allowable (maximum) percent gold. The maximum ratio of gold finish thickness to solder alloy thickness can be calculated, to help prevent a problem from excessive gold-tin (i.e., AuSn4) compound. For the equation and its derivation, please refer to a paper of mine, "The Use of Capillary Action Measurements for Solderability Improvement," Soldering and Surface Mount Technology, No. 9, Oct., 1991, Wela Publications, Ayr, Scotland, Table 5. It is interesting to note, The Embrittlement culprit, AuSn4 is 29 weight percent gold. So even if one had 100% tin as the solder alloy and 10% gold were dissolved into the solder, then about a third of the solder joint would be rocks (i.e., compound) and the remainder would be soft solder. Do not count on the rocks to bond to the solderable surface. Hence most recommendations I have seen have been in the 3 to 5 weight % gold range for the maximum allowable percent. Gold is dissolved by molten tin based solder, but the gold does not go into solution (i.e., the result is not a solid solution). For more details on the mechanism and explanation, please refer to a paper of mine: "Understanding Gold Embrittlement in Surface-Mount Soldering," ISHM's 1st Joint Technology Conference, San Diego, March, 1990 (//WWW.ISHM.EE.VT.EDU). Incidentally, ISHM changed its name to IMAPS, (703) 758-1060. The above represents my own view, and not necessarily that of my employer. --------------------------------------------------- Mike Wolverton Texas Instruments [log in to unmask] ------------------ Original text From: "ddhillma" <[log in to unmask]>, on 3/20/97 5:50 PM: To: [log in to unmask] Cc: [log in to unmask] Hi Tom - The words gold embrittlement really mean job security for metallurgists! You would think that as well researched and investigated the gold embrittlement mechanics of failure has been over the last 20 years we would stop making the same mistakes. Two rules of thumb to follow: a) Is there enough solder volume to allow the gold to uniformly go into solution? b) Is the soldering operation of sufficient temperature and time to allow (a) to occur? The thickness of the gold finish isn't the only deciding factor of having a solder joint embrittled by gold/tin intermetallics - the process is equally important. Also, you can avoid the whole gold embrittlement issue by keeping the gold below 10 microinches but you then have to deal with poor solderability on the components if this thin gold plating is of poor quality (and plating a quality gold finish below 20 microinches requires good control and knowledge of one's plating system). Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Gold Embrittlement Author: [log in to unmask] at ccmgw1 Date: 3/19/97 3:17 PM To those who have heard enough of this subject I send my deepest apologies, but to those who still have some energy left to help a double 'E', who has found himself doing a lot of PCB design lately, I need to try to obtain some information on Gold Embrittlement. My question is: Can SMT components be attached to PCB's, which are fabricated using 50 micro inch 'Hard Cobalt Gold' over 200 micro inch low stress nickle, without having to worry about Gold Embrittlement, and if so, are there any special process steps which need to performed or monitored. We are using a mixed bag of SMT packages with 1mm pitch being the finest. I have encountered conflicting data on this subject so far. Thank you Tom Guerriere Staff Engineer Controlotron Corporation (516) 231-3600 x81 [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] * *************************************************************************** *************************************************************************** * 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] * *************************************************************************** *************************************************************************** * 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] * ***************************************************************************