hi, so maybe eric found a way to keep the intermetallic from oxidizing. phil -----Original Message----- From: Wenger, George M. [mailto:[log in to unmask]] Sent: Tuesday, November 13, 2001 10:07 AM To: [log in to unmask] Subject: Re: [TN] Intermetallic Layers Dave, Right on! That is our experience also. That's one reason Lucent has an internal specification for surface finishes. This specification lists exceptions to industrial specs like IPC. We are not comfortable with a "minimum coverage" spec for SnPb HASL because we've had many experiences where 50 microinches or less of solder has caused severe soldering problems. The failure have almost always been linked to oxidized copper-tin intermetallic. Boards with thin solder (i.e., exposed and oxidized copper-tin intermetallic) have successfully been re-used by re-hasling with agressive water-soluble-fusing fluids which removes the oxide and allows fress SnPb to "stick" to the IMC. Regards, George George M. Wenger (908)-546-4531 [log in to unmask] Celiant Corporation 40 Technology Drive Warren, New Jersey 07059 -----Original Message----- From: David Hillman [mailto:[log in to unmask]] Sent: Tuesday, November 13, 2001 12:25 PM To: [log in to unmask] Subject: Re: [TN] Intermetallic Layers Hi Eric! Sorry but I humbly disagree. There is an abundance of published industry data which shows that oxidized Sn/Cu intermetallic is one of the more unsolderable surfaces encountered on an assembly. Problems with poor plated thru hole fill due to "weak knees" (thin solder causes the Sn/Cu intermetallic at the hole rim to become oxidized) and thin HASL coatings are just two examples of everyday industry solderability issues associated with Sn/Cu IMCs. What type of flux did you use in your testing? Very aggressive flux chemistries will allow the soldering of Sn/Cu IMCs but a fair majority of the industry is moving away from these types of flux formulations. With all that being said, without the Sn/Cu IMC we would have no solder joints so it is a critical part of a solder joint. Dave Hillman Rockwell Collins [log in to unmask] Eric Dawson <[log in to unmask]>@ipc.org> on 11/12/2001 07:49:56 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]> Sent by: TechNet <[log in to unmask]> To: [log in to unmask] cc: Subject: [TN] Intermetallic Layers Hi All, I notice that a few new references have been made to the above subject and thought I would share some of my early work with you. In my first post as a graduate, I researched the causes of dewetting on circuit boards. I came across a solution, the make-up of which I have since lost, which dissolved the tin lead alloy but left the two intermetallic layers. I produced a number of one inch square coupons which I soldered using 63/37 alloy, RMA flux and a Tri Moore Rotary Dip Tester. These were divided into three categories: 1 Control 2 Remove tin lead and re test in the Rotary Dip. 3 Remove tin lead, Several hours steam ageing and re test. Microsections showed that I had taken off the alloy successfully and left the IMC.s. All of the re tested coupons soldered successfully, including the steam aged ones. This was some years ago so I cannot remember the etchant nor the hours and conditions in the steam ageing equipment. I do remember that the IMC soldered very well so I am always dubious when somebody blames the intermetallic for poor soldering. I seem to be alone in my faith that the IMC solders but this was the result of my very own work and I stand by it. Regards Eric Dawson, Defender of the IMC. ------------------------------------------------------------------------ --------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------