Hi Ian! I am keeping my fingers crossed. I also talked with my buddies at the Rockwell Science Center (our old think tank) and we have another phenomena working in our favor. The aluminum oxide should impact the galvanic couple "connectivity" by impeding the current flow. Dr. Tench felt that the Al2O3 and the anode-to-cathode ratio may be enough to inhibit a galvanic reaction for many use environments. I am going to have Dr. Tench also create the finish polarization curves which should help demonstrate that we are in a passive and not active region of the electrochemical reactions. Lots of fun - I haven't studied this much galvanic science since my junior year in college. It is also a nice data point to see that my test results are in agreement with what you experience in real life. I'll let ya know who the salf fog testing progresses. Dave "FOX, Ian (York Rd)" To: [log in to unmask] <Ian.FOX@GOODRICH cc: .COM> Subject: Re: [TN] Heat transfer from ENIG board to aluminium casing Sent by: TechNet <[log in to unmask]> 03/18/2003 08:44 AM Please respond to "TechNet E-Mail Forum."; Please respond to "FOX, Ian (York Rd)" Dave, glad to see your testing so far mirrors what I found, i.e. no corrosion with ENIG and conversion coated Al. Good point about the anode/cathode relationship though. To contribute to answering Daan's question, I agree with both yourself and Brian, contact area is the key to thermal performance. Provided that the Al surface finish is reasonable there should be no practical difference between either of the two finishes. If you have a rough cast finish for instance you might argue that the HASL finish would couple better with the Al due to its ability to deform, but I suspect any difference would be marginal. Ian Fox Goodrich Engine Control Systems -----Original Message----- From: Dave Hillman [mailto:[log in to unmask]] Sent: 18 March 2003 13:47 To: [log in to unmask] Subject: Re: [TN] Heat transfer from ENIG board to aluminium casing Hi folks! Let's look at some numbers! The thermal conductivity (in W/ m K in the 0-100C range) is 237 for Al, 318 for Au and 66.8 for Sn. You should have better heat transfer by going way from Sn - but as Brian described the thermal transfer game is ruled by surface contact. Brian also mentioned the issue/question of galvanic compatibility, the same question I queried the TechNet community on several weeks back. I received a number of good information leads but nothing as definitive as I was looking to obtain. Here is an update to that question - I began a series of tests: the silver/aluminum and gold/aluminum galvanic couples test vehicles (circuit boards with the appropriate finishes coupled to Al casings by Al standoffs and having a 5 volt bias) have completed 250 hours of 85C/85%RH with no issues of galvanic compatibility! The salt fog tests begin next week and I'll keep everyone updated as those tests progress. It appears that the anode-to-cathode relationship is a key parameter in equation. Dave Hillman Rockwell Collins [log in to unmask] Brian Ellis <b_ellis@PROTONIQ To: [log in to unmask] UE.COM> cc: Sent by: TechNet Subject: Re: [TN] Heat transfer from ENIG board to aluminium casing <[log in to unmask]> 03/18/2003 06:54 AM Please respond to "TechNet E-Mail Forum."; Please respond to Brian Ellis Daan I would have thought exactly the opposite! An uneven HASL surface will have fewer contact points to the aluminium than a flat ENIG surface. That having been said, I would have thought that both would be bad, electrochemically speaking, if subjected to humidity. From very poor memory, the Al-Au couple is somewhere about 4 V, roughly double that of Al-Sn/Pb. Brian d. terstegge wrote: > Hi Technet, > > We are in the process of converting some of our boarddesigns from HASL > to ENIG conductor finishing. Now one of our designers is worried about > the effect that this change may have on heat transfer from the plated > board-edges to the aluminium casing on which the board is mounted. He > feels that the heattransfer from leadtin to aluminium is better that > for nickel/gold to aluminium, possibly resulting in heat problems in > the end product. > > Any ideas on this ? > > Daan Terstegge > Thales Communications > Unclassified mail > Personal Website: http://www.smtinfo.net > > --------------------------------------------------- > Technet Mail List provided as a free service by IPC using LISTSERV > 1.8e To unsubscribe, send a message to [log in to unmask] with following > text in the BODY (NOT the subject field): SIGNOFF Technet To > temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/archives > Please visit IPC web site http://www.ipc.org/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or > 847-509-9700 ext.5315 > ----------------------------------------------------- > > > --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------