For some of you, the following will be a little humorous and to others scary. Last month one of our CMs called me and asked if I knew of an engineer (who will remain anonymous to protect the guilty) that works in my building. I said yes, why do you ask? Well, he says, she sent me some pictures of three capacitors that had what looked like whiskers. She was claiming that these whiskers caused a short on her board. (Of course implying that the whiskers had something to do with the board assembly.) Looking at the pictures I was amazed at the growth of whiskers on the capacitors. It looked like something from a 1950s sci-fi movie. So I asked if an analysis of the board had been done. Yes, she replied; it is contaminated with chlorides. Well, looking at the SEM report there was something very strange. Not only was there chlorine on the board, there was a witch's brew (no pun intended) of elements present. Na (sodium), Mg (magnesium), Al (aluminum), Si (silicon), P (phosphorus), S (sulfur), Cl (chlorine), Ti (titanium), Sn (tin), N (nitrogen), O (oxygen), Zn (zinc), Pb (lead) After reading the report, I needed to see the board for my self. Wow, the first thing that I saw was a visible dendrite TREE that was about an inch and a half long (~38 mm for the rest of the world) headed for ground. Under the microscope I found evidence of oxidation and etching of the solder joints and leads on some I.C.s and passives. The board was a prototype and as such there had been many wires and components soldered on and off since the board was received three months ago. There was evidence of flux on the board that was dried but the Alpha 711 flux that we use couldn't etch away copper. I needed to figure out what was this contamination and how it occurred. I had noticed a few weeks ago that a tech was using a grinder in the lab. This would probably account for the aluminum, silicon, titanium and magnesium. And maybe the sodium was from someone's snack. But the chlorine and zinc were puzzling. I was back at my desk when one of the techs came by with an almost empty bottle of Eutecsol 682 flux to show me. Yes, what's your point? He said that this bottle of flux was full last year and that the engineer that bought it had never used any. Really, what is it used for? He said, it's for soldering to stainless steels. Wow! I looked up the MSDS and found that the flux contained the following. Ethylene Glycol Zinc Chloride Hydrochloric Acid Ammonium Chloride Well now, that explains it. Although no one would admit to it, it seems that someone ran out of the Alpha 711 flux and finding the Eutecsol 682 discovered that it cleaned the solder pads much better and faster. Not wanting to settle for the slow reacting Alpha 711, Mister-Nobody filled the empty 711 flux bottles with Eutecsol 682. I was thinking, had the whiskers not grown across and shorted the capacitors the failure mode might have been the disappearance of the circuit board. (Heee) Donald Kyle C.I.D.+ --------------------------------------------------------------------------------- DesignerCouncil 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 DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------------