Cristina, The cracking of solder joints on electroless nickel and immersion gold finish is being more often reported as more people are using it and multiple soldering operations are being employed. The problem is probably not the gold which is only about 5 microinches thick, but an interaction of the nickel and tin in the solder. In a study that I am familiar with, they determined that boards that were plated with electroless nickel and immersion gold, soldered and then underwent a burn-in cycle of about a week at 150 deg C experienced considerable solder joint cracking. The joints failed at the solder/nickel interface leaving a clean land with no solder retained. The metallurgical mechanism indicated that as the board was thermally aged, the nickel moved into the solder forming tin/nickel intermetallics, and left all the phosphorus behind. The layer underneath the solder jont was initially about 6-8% by weight phosphorous or about 25 % by volume and after aging the immediate layer jumped to about 16-20 percent phosphorous by weight or about 60% by volume and the joint became very weak and the parts fell of during shake, rattle, and roll. Multiple solder operations without the benefit of the burn-in also produced the same cracxking but it was considerably more random and some did not fall off after five solderings. The tin/nickel intermetallic grows in solid state and increases as temperature increases, this intermetallic growth also increases as more time at soldering temperature is added by more soldering operations. It must be noted that the intermetallic growth itself probably is not a bad thing, but what is left behind is probably the culprit. A comparison test with electrolytic nickel gold of similar thicknesses did not produce the same joint failure. The study was unpublished and I can not send you a copy. Above is one scenario or the nickel/gold solder failure. Another is fairly common wherein the supplier found that all of the lands did not plate in the electroless nickel process and so he gave it light scrub, and replated it, the adhesion between the multiple plates is not great. The joints having double plating will often crack after a little stress and often exhibit gold at the crack. A microsection of the joint will determine if this is the cause of failure. A third failure system that I have seen with EN/IG is that there is too short of a dwell time at the peak in the soldering profile. The failed joints will often exhibit a gold color on the cracked joint, and it appears that the solder soldered to the gold but not the nickel and it peeled off of the electroless nickel A small increase in peak soldering temperature or a longer dwell time can eliminate the problem. There are some out there who have decided that the profile for HASL coated boards must be used for all finishes, I and some others do not agree with this. Hope this has some relevance to you questions about nickel/gold solder joiints. Phil Hinton ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################