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Mixed Technology - Which First
We have just put in place our first assembly line and are assembling a mixed technology circuit board. We assemble the through hole section first using our wave system, then the SMT parts using a reflow process.
Is it always done in this order? Can the order be reversed?
S. S.


You could potentially run the through hole first. However, you should read the specs on the components beforehand. Many through-hole components are not compatible with SMT because they simply cannot take the heat of the reflow oven without being damaged.

But it all depends on the boards you build. If they are single sided I would always run SMT first then go to a stuff line for the operators to put in through-hole parts. Then I would run it in the wave.

It's a little different if you run double-sided boards. In those cases, I would run the boards as normal in the reflow with one exception: On the simple side of the board -- typically the bottom side -- I would glue the through-hole components to the board.( I define "simple" to mean mostly resistors and capacitors.)

After the glue cures and exits the reflow oven,send the board to the stuff line with the leads protruding from the simple side of the board. If yours is a dual wave machine, the SMDs and through-hole parts will be soldered simultaneously on the pass.

If both sides of the board are extremely complex you can continue the procedure you are now following so long as parts are not being damaged. Better yet, invest in aselective soldering machine. Most have around a 1mm keep-away and can solder through-hole parts easily.

Chris Ellis, Sales Manager

Chris Ellis is a Sales Manager/Engineer for Manncorp with 19+ years experience in the PCB assembly equipment industry. Chris worked as a Manufacturing Engineer for 5 Years. Prior to going into sales, he was with PCB assembly equipment suppliers. Before joining Manncorp, Chris was an independent rep in the Carolinas for several years.
Chris Ellis

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