Sehr geehrter Herr Englmaier,
ich möchte mich gerne für die kompetente und unbürokratische Hilfe bei unserem SMT-Fertigungsproblem bedanken. Bei ihrem Besuch in unserem Hause haben sie sehr gezielt die möglichen Ursachen durch eine ganzheitliche Analyse des Istzustandes herausgearbeitet. Unsicherheiten die bis Dato bei uns vorhanden waren sind beseitigt worden und wir können nun gezielt an die Umsetzung ihrer Vorschläge gehen!
- The issue you have with some passive components not being soldered properly and thus showing cold joints (Ablieger) is due to a failure referred to as “Backward compatibility” issue.This is when a lead-free component is soldered with a SnPb solder paste. The melting point of the solder paste is at 179°C-189°C and peak temperature around 220°C (board depending). The component metallization is Pb-free but is not specified. This can be Sn, SnCu, SnCuAg, …, fact is that the melting point will be above 217°C with a required peak temperature of at least 235°C.
Current profile is therefore too cold and time above reflow too short to create proper solder joint formation.
We also suspect that due to board layout some areas of the board will absorb more heat because of inner copper layer and will thus require more heat imput to come to the required temperature status.
We therefore advise to increase the reflow profile with at least 5°C and 15 seconds above reflow.
We also have contacted company ….. in order to assess if removing the 4 protective plates form the nozzles in the peak zone will increase the temperature output of the …. oven. We have not yet received any feedback on this subject.
It is however clear that the reflow oven has reached its technical limits and will only allow for very minor adjustments towards reaching higher peak temperatures and longer times above reflow.
- It is also clear that the … oven will not be able to solder lead-free components with lead-free solder paste at acceptable conveyor speeds.
- We also have seen that placement of chip components is not 100% to the center between the two pads. This can easily lead to tombstoning or “Manhattan” effect, especially when one side of the component will be sitting on a bigger volume of paste. This side will be pulled down more by the melting solder paste during reflow and cause (minor) lift of the component resulting in a cold joint (Ablieger) or in worse case in tombstoning.
- I have attached a few papers on backward compatibility for your reference.