I'm wondering if it's possible to desolder all smd components on a PCB using a reflow oven? My plan is to hang the PCB upside down over a piece of aluminum foil, use a standard reflow profile and let gravity do the work. Saving the components is not a concern, only desoldering them. What would prevent this plan from working? Will surface friction prevent some of the smaller components (e.g. 0402 or 0603) from dropping?
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\$\begingroup\$ Surface tension rather than surface friction. \$\endgroup\$– TransistorMar 13, 2020 at 21:45
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\$\begingroup\$ Unlikely to work, most 0804 and smaller components aren't heavy enough to drop off. Use a hot air gun and a pick or tweezers to move components off the pads once the solder melts. \$\endgroup\$– Phil GMar 13, 2020 at 21:54
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2 Answers
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Surface tension tends to hold small parts in place, but if you bang it in a hard surface after getting the solder molten, that'll get most parts off.
answered Mar 14, 2020 at 1:09
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No, that's not likely to work. Generally, for small parts, the surface tension of the solder is sufficient to hold the parts in place.
In fact, for two-sided boards, that need to go through reflow twice, small parts that will be upside down for the second pass do not need to be glued in place.
answered Mar 13, 2020 at 22:00
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\$\begingroup\$ Thanks. What is the best desoldering method if you want to remove all components from a PCB and preserve the PCB as best as possible? \$\endgroup\$– JonMar 13, 2020 at 22:14
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2\$\begingroup\$ @Jon I would recommend using a hot air reflow gun and just removing the parts with tweezers. 500°C works well with relatively good air flow (work quickly and don't continue heating any one area too long). Smaller parts such as 0402 passives often will blow off the pad if the flow is high enough. \$\endgroup\$– JYeltonMar 14, 2020 at 0:04
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\$\begingroup\$ I think the way to phrase it is that small components are almost guaranteed to remain in place when the board goes through reflow, even if thy are on the "bottom" (i.e., side facing toward center of earth as opposed to side facing toward the sky). \$\endgroup\$ Mar 14, 2020 at 1:27
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\$\begingroup\$ also Keep in mind that on 2 sided PCB that the SMD components on the bottom side are likely to be glued in place to keep them from from falling off during reflow when the board was made. +1 for hot air gun and tweezers. You can also get a heater that goes under the board to pre-heat it so it is easier to quickly spot heat the individual components with the heat gun to get them above the melting temp. \$\endgroup\$– bigjoshMar 14, 2020 at 3:30
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\$\begingroup\$ @bigjosh What about just using a hot plate to heat the board up to solder melting temperature and use a scraper or silicon wedge to wipe the components off all at once? \$\endgroup\$– JonMar 21, 2020 at 4:45