![]() All kinds of input, both personal reflections and/or links to relevant documents are highly appreciated. Personally I doubt that and my gut feeling is that they are clueless and are in a state of total denial. Our PCB assembler claims that they can use approx 225'C and compensate the lower temperature with longer time above the liquidous temperature of the solder paste (183'C). Both Murata and Diodes points out in datasheets and appnotes that Matte Tin finished components must be soldered with a peak temperature above the melting point of Tin (232'C). The SMC package is on of the larger components on the PCB, so it could be related to temperature. Oxidation due to unproper storage conditions has been discussed but the actual shelf time at the assembly house is less than a month and in a sealed plastic bag. We have also seen signs of poor wetting on SMC diode packages where in one case only half of the soldering terminal had a nice solder slope. The two different metal alloys in the joints will have different thermal properties and cause mechanical stresses and cracks during thermal cycling. As pure Tin melts at 232'C, the surface material on the components is not melted by the solder paste, thus they will not form a fully mixed soldering joint. ![]() Automotive application -40'C to +85'C ambient and locally up to 110'C on the PCB surface Lead free components, mostly with matte Tin finish on the solder terminals Leaded solder paste, SnPb 60/40 or SnPbAg 60/37/3 (Demand from some customers) SMD packages 0402, 0603, 1206, SMB, SMC, SOT23, QFP44, pin header 2x2 Dual side assembly, ie two runs through the assembly and soldering line 6 layer PCB, FR4, gold plating on all solder pads, RoHS compatible All copper plane solder pads have thermal relief Peak temperature during reflow is just reaching 230'C for a single panel My idea, so far, is that the peak temperature during reflow is a bit too low. I think I have found a possible root cause to the issue, but I lack someone to ask for a second opinion and look with "fresh eyes and mind". Presently i'm investigating an issue with broken soldering joints on a PCB that has been thermo cycle tested.
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