Reflow temperature setting

Hi,

I use convection reflow and both top & bottom settings are the same.

Is the part too heavy to rely on surface tension? there is an equation that can determine this (aswell as real test i.e. part falling off) We have some SIM Card holders on bottom of boards which we have to glue to prevent it from dropping off on the second pass.

aj...

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Hi First I think you have to analize your PCB design. Heavy weight components should be gathered on one side of PCB. As I think, if you want to reflow both sides simultaneously there might be a problem. A chance that large components will drop off the bottom is very big. The largest package which can almost 100% avoid dropping is S08. So if you have big components on one side and smaller on another you can try to reflow the PCB (heavy side up). Better way is two stages of reflowing. First you reflow "light" side of PCB, then turn it upside down and solder the "heavy" side. It's more reliable. The reflowing of solder joints and dropping components from the bottom side (with light components)during second stage is unlikely. Solder paste embraces the flux which helps to transfer heat during soldering. When you reflow first side of PCB flux helps to reflowing and evapourates. Then you reflow second side (already reflowed side is in the bottom). During second stage you will reflow only solder paste and not reflow solder joints on the bottom (because there is almost no flux/heat transfer). In this case you can use the same temperature profile for both sides. Anyway you should check for PCB design. Hope it helps Sorry for my English

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EC - I hope you don't mind that I add to your question... We are running lead free assemblies now and parts that normally hang on upside down are falling off. Any advice on this from others new to lead free?

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