Transcript
Phil
Welcome to Board Talk. This is Jim Hall and Phil Zarrow of ITM, also known as Pick and Place, the Assembly Brothers, here to attempt to answer your assembly and process questions regarding SMT.
Jim
Today's question comes from D.L.
What can cause a 0603 passive component to blow off the circuit board during reflow as if a firecracker was put underneath? That's a pretty graphic description.
Phil
That's radical. Well, the first thing that comes to mind is a firecracker under the component? Maybe you have some prankster in your assembly department. A couple thoughts on this. The question we want to know is if it is accompanied by splattered solder paste?
Jim
I am curious why this person would choose to use the words "as if a firecracker blew off" because I'm thinking of how you're going to know this. The board goes into the reflow. It comes out. The part is missing. Why would you describe it as a firecracker unless there was some evidence of some sort of explosion, which would lead us to believe that it would be solder paste-related.
Phil
Generally, we think of solder paste-related violence - eruptions of a volcanic nature. Typically, we find this is similar to out-gassing and that's usually due to too rapid a preheat.
Jim
Preheat slope too high.
Phil
Now, what if there isn't any solder paste there? The component's is gone.
Jim
My experience as a former oven manufacturer, listening to complaining customers, is that many displaced components relate from oven problems. Conveyor vibration has always been the biggest.
Align your conveyors, lubricate your conveyors, because if they're vibrating during the reflow cycle, during the ramp-up and before you actually start wetting, those components can move.
Phil
The key word here being "blow off" is improperly set or maladjusted convection. Either the blower's set too high, somebody's tooled around with the buffers and some of the other stuff, or since a number of machines have adjustable convection levels, somebody cranked it up too high.
Jim
Or a more benign maintenance issue is you've got some flux or materials blocking up some of your hole pattern causing a high-velocity jet or an improperly directed jet in one part of the furnace. So, your 0603 goes under there, gets hit by this blast of air and, whoosh, it's gone.
Make sure you're really profiling the actual board you're running. Put a thermo-couple on the area; the type of chip that you see being blown off; measure what the real, actual preheat slope is.
If you've got conveyor vibration, you can usually feel it by just observing it. Air flow issues are a little more subtle to diagnose.
Phil
We hope that helps. This is Phil and Jim, the Assembly Brothers. So, again, in the meantime, I can highly recommend - don't solder like my brother.
Jim
And don't solder like my brother.
Phil
And don't let the kids fool around with the convection controls on your oven.
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