Whatever and to whomever interested, whohaw is supposed to be wohaw to get away from the film in which what's her name got naked and starred. Demi? Anyway, the following is what ended up this way - partly. Whohaw Guenter, Your're fine and your messages are all received well. I just never knew you had to remove the intermetallics, and with a glass brush. That's all I meant. I'm the one who's been on holiday. Even though only a few weeks, I must have missed something during that time. You're helping me see more things than ever before. Thanks a million times over. And you know I like stirring the pot. Hell, I just can't help it. Please enjoy and thanks again, MoonMan ----- Original Message ----- From: "Guenter Grossmann" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, October 25, 2001 8:14 AM Subject: Re: [TN] AW: [TN] Antw: [TN] exposing intermetallic on BGApads... Hey Moon Man What bomb? Do you mean my comment about intermetallics? Well, gotta rub my eyes, I never meant doing something wrong and I even didn't get the irony in your comment. Seems as if I am still in a holiday mood. You hoped to see something more from me. Hmmmm. What should I say? - Every soldering process produces an intermetallic layer - Intermetallics don't wet to my knowledge and I mean to know that this is due to the formation of very stable oxides that won't solder either. If you desolder and remove the remaining solder there is a real chance that you expose intermetallics. More likely if you remove the solder thoroughly. I had a case this summer that had nothing to do with rework but with repeated reflow solder operations. The solder joints didn't look bad, but on the pads that where not printed dewetting of the HASL could be seen. When we made microsections we saw that the solder joints had areas where the solder was touching the IMC but we observed a thin dark line. I wasn't sure whether I see a preparation artefact or a real thing. However, 2 joints we looked at had a clear separation between the IMC and the solder some um long and I believe this was due to exposed intermetallics before the printing took place. In the dewetted regions no solder was present on the copper only intermetallics. Sorry, that I upset you, I didn't mean to but I stand to my point: If you repair and remove the remaining solder there is a good chance to expose intermetallics, maybe only partially, and no soldering takes place in the spots where the IMC was exposed. Best regards Guenter Guenter Grossmann Swiss Federal Institute for Materials Testing and Research EMPA Centre for Reliability 8600 Duebendorf Switzerland Phone: xx41 1 823 4279 Fax : xx41 1823 4054 mail: [log in to unmask] Never a bother. Love the joke and say hi to the kids. Besides the glass brush, my biggest concerns are about fine pitch and BGA device types and the solder termination area topography they require (flat) to effect placement, continued alignment, and subsequent reflow and "acceptable" solder joint formation. As you know and have observed many times, once device removal is effected, the solder left is very uneven, to say the least. This, again as you know, is why we wick off the solder left after the removal process. This, then, is the dilemma as I see it. In your terms, we now expose an IMC layer, to whatever extent, preventing solder "wetting" in some areas. I guess, this is a random occurrence (where and how much IMC) is left. Therefore, doesn't this point to sh luck to again effect "acceptable solder joints? Enjoy your kiddy romp, Earl ----- Original Message ----- From: "Guenter Grossmann" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, October 25, 2001 8:37 AM Subject: Rework Sorry for bothering you again but I just had a thought: 1) Someone doing a job thoroughly an clean does his / her job good 2) Doing a job only partially is bad workmanship 3) Thoroughly removing solder exposes IMC and produces bad solder joints 4) Partially removing the remaining solder protects the IMC and leads to acceptable solder joints according to MIL and ESA standards ERGO: MIL and ESA standards support bad workmanship ( just a joke that came to my mind before I go of to play with my kids) Have a great day Guenter --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------