|Ask the Experts|
February 19, 2007
Wave solder and reflow 0805 capacitors and resistors
We will need to expose some 0805 SMT caps and resistors to both a reflow oven and a wave (lead free) to accomplish the soldering on this 2 sided dual technology board. Are we overexposing the parts to too much heat by doing this? Will we be impairing life of the parts? The parts will be glued in place as they are pick and placed on the board, and the wire looms will be hand inserted before waving the board to solder the wires into place. Can you offer advice?
|Expert Panel Responses|
What you will find in SMT is that there is basically one rule: there are no "rules". What I mean by that is that every application is different. So pastes are different for different applications. And components are different, etc, etc. In this case the "general" answer is: of course, people have been wave soldering R's and C's on the bottom side of boards for years. But your application could be one where the particular parts being used can't stand the heat. Best recommendation is to contact the component vendor and get the specs on the parts themselves to make sure they can withstand the two thermal excursions. Your issue is especially poignant and appropriate right now as we are transitioning to Lead Free processing. With Lead Free, the reflow profiles are getting hotter. So you may be in spec right now for wave and a eutectic reflow profile. However, the lead free profile adds 30 deg C to the peak temp and this could take you out of the comfort zone for the part. Suggest you put this back in the vendor's lap to figure out and you will be in good shape. (Vendors give free consulting! ) Thanks! If there are any questions or if additional information is needed, please feel free to ask.
Heller Industries Inc.
Can you select a pallet to prevent the SMT parts from being hit by the wave solder? The resistors should be fine with the double exposure, but there is a slight risk with the ceramic capacitors. What is the thickness of the ceramic caps and the dielectric? This plays an important in assessing your risk. If the caps are C0G/NPO and relatively thin, no problems. If the caps are X5R and 0.8 mm thick or greater, you could have issues.
CEO & Managing Partner
As long as you are careful with the preheat zone so that you do not ramp up too quickly you components will be fine.
Regional Sales Manager
OK International Inc.
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