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Im trying to reflow some RF pcbs in a legit reflow oven. The PCBs material is "Rogers RO4003 305 Um" and 3 layer. (Its a very thin pcb)

If temperature is high enough to reflow the paste, the pcb changes color , and gets a little burned, degrading its usability.

paste type : CIF Sn96 5Ag3Cu0.5 no lead

oven: CIF FT 03 (its a 2 heating element: quartz tube)

please suggest some hints to improve soldering process.

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  • \$\begingroup\$ A legit 6-zone conveyorized oven would probably help. Batch ovens are probably not capable of meeting the temperature profile spec. Pb solder is easier. Usually PCB makers try to dissuade odd layer counts because of warping, but I’m not familiar with your particular material. \$\endgroup\$ – Spehro Pefhany Oct 24 '18 at 9:16
  • \$\begingroup\$ Infrared/quartz without any type of internal fan has too many hotspots for this to work. A hot plate may work better. \$\endgroup\$ – Erik Friesen Oct 24 '18 at 11:36
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Yeah, these non-pro ovens have a pretty nasty rep. There may be a "sweet spot" in the oven somewhere. I do pretty good by doing small batches in a toaster oven that I retrofitted with a heat-ramp-soak controller from Omega, and putting a thermocouple directly on the board. especially after insulating the walls of the oven.

If there's a way to move the temp sensor to be in direct contact with the board, do it.

Other than that, all of these non-pro solutions, my retrofit included, take some hours of cycling through while measuring, to tweak out the ramp-soak profiles. Ya gets what ya payz for.

Also, if I may, you don't use an oven like this for real quantity. Therefor, if you don't need to use lead-free, don't!! You have less of a chance of burning up your board at a lower temperature. In addition, you might think of this as a prototyping step. Use your oven to inexpensively knock out prototypes, test them, then ship off board assembly to folks with the right gear.

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We've played this game with a batch quartz oven with awful results. To see what's really going on, instrument a pcb with a matrix of thermocouples and monitor the temps. Chances are, you won't like the results.

Keep running tests, changing one variable at a time, until you get better results.

Things you can change:

  • Profile times and temps. There is probably a solution, but you have to find it. Try to align recorded temps with the published reflow profiles from the pcb/component manufacturers.
  • PCB position on the tray. Use the thermocouples to detect hot-spots, move the pcb to find the most-even temperature area.
  • Adjust the Convection air flow.

Off course, all of these adjustments are interacting, so this procedure is a real PITA. There's no easy way to go through this, except step-by-step. Once you get a 'feel' for your oven performance, and different PCB's, then it gets easier but process never becomes 'Automatic'.

Good luck!

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