Pdf lead free solder and flex cracking failures in. I have worked with many lead free solder wires at work and although they are all different, the end result is always a dull looking solder joint. Ray prasad troubleshooting smt yield problems in a lead free world 1. The surface of cold joints appears dull, lumpy and pockmarked. Apply heat evenly to the part wire and the solder pad just for the time it takes for the soldering tin to flow around the part. It would not take much force to bend that lead over to touch an adjacent trace. Soldering is a process in which two or more items are joined together by melting and putting a. Lead free soldering and bad looking joints electrical.
Reflow profile has significant impact on leadfree solder joint performance also because it influences. The flux will burnup if you solder to the iron and not close to where you are soldering on the actual joint itself. Conventional solders contain lead, which is poisonous. Common soldering problems adafruit guide to excellent. A solder joint like that is a self destruction joint which will loose electrical connection sooner or later. The flux core in the wire and lead free fluxes contain harsh reducing agents that are highly irritatating to wet membranes like the sinuses and the eyes the flux used in lead free soldering has a shelf life.
If it gets all burntup on the iron, you will notice the solder not look as shiny and smooth the more it gets burnt away. Cold solder joint the definitive guide to soldering. Leadfree solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc. The newer solder formulation, of 95 percent tin and five percent antimony, is the most widely used replacement for lead solder. Pdf solidification shrinkage defects in electronic solders. Changwoon han and byeongsuk song, development of life prediction model for lead free solder at chip resistor, 2006 electronics packaging technology conference. Therefore, in this study two leadfree solder alloys sn96. Cold solder joints are dull and sometimes cracked or pockmarked. Using a magnifying glass youll see the solder spot filled with little craters which make the joint look dull. A solder joint failure could be caused by crack initiation and growth or by macroscopic solder facture.
Acceptable leadfree and tinlead connections may exhibit similar. All leadfree sections are highlighted in green to speed lead. Solder is a fusible metal alloy used to create a permanent bond between metal workpieces. Why arent my solder connnections shiny and perfect. Some people said about this solder, that it contains 4% of silver ag, so the joints are shiny and indistinguishable to normal sn60pb40 joints. Cold solder joints often appear dull and make convex mounting on the pins and the board flex areas. Lead free joints have a dull surface and higher wetting angles. The flux is important in cleaning the surface you are putting solder to and is activated by heat. Hi, some days ago, i tried to solder lead free the first time in my life. It remains shiny in appearance and may dip slightly where the pipe. Solder crack countermeasures in mlccs multilayer ceramic. Lead free solder, which started to be used due to environmental considerations, has properties of being rigid and fragile, and has a higher risk of solder cracks compared to conventional eutectic solder.
Unfortunately, most leadfree solders are not eutectic formulations, melting at around 250 c 482 f, making it more difficult to create reliable joints with. The solder bond will be poor and the cracks may develop in the joint over time. As companies start to implement lead free soldering processes, hand soldering and. What you are seeing is a change in surface texture. As already noted, a cold solder joint is a solder joint problem that often occurs during soldering when the solder fails to melt entirely and flow to form an ideal solder joint. Liu and yihsin pao, fatiguecreep crack propagation path in solder joints under thermal cycling, journal of electronic materials, v 26, n 9, 1997. Dull grainy solder joints insufficient solder reflow. Images of a disturbed snpb solder joint defects and b striated acceptable leadfree solder joint normal. This occurs when the solder transitions from liquid to solid. If not properly rectified, cracks will be more likely to form over time, leading to eventual failure.
169 964 1212 470 476 785 1290 424 698 813 1100 1388 1072 508 322 565 686 1306 640 1139 618 1601 1341 1248 33 385 193 1597 1228 1556 991 1361 1184 627 1295 897 998 1454 63 47 39 535 1182 123 1397 1363