![]() ![]() But we still see something much more like the desired profile shape. The burner can only raise this one’s temp a deg/sec, while the thin plate can go 2 deg/sec. Again manual fan control, but I turned it on just at start of soak and only turned it off several seconds before soak ended. Of course the TC was on top of the plate and directly in the fan breeze, so its temp was probably more strongly affected by the fan than the plate was. The shape looks a lot more like what we want. I manually controlled the fan (several cycles) to keep temp about even during soak phase. OK, let’s try 2 things: smaller, thinner aluminum plate (3.75 x 5.5 x 0.05″) and a fan when heater power is off. I suppose if we power-controlled the fan so it was only on when power to the burner was off… Yeah, it wouldn’t take any extra parts or pins (besides the second solid state relay) if I just connected the fan relay between the current relay drive pin and +5 instead of gnd, thus inverting the logic. If I put a fan on it, the “coast” time would be less, sharpening the knee at soak start, but the burner would have to work harder to heat it all up, so the rate of temp increase would also go down. The well for the TC would be a lot harder on a piece of 1/8″ aluminum… I suppose I could just use a smaller, thinner plate. The main culprit is probably the thermal mass of the aluminum plate, but I really want the plate to provide uniform heating of the PCBs. It looks like the frequency response is way too low to shape the curve much. (I was impatient and that one started at almost soak temp so you can’t see the initial ramp up.) Rats. – power on ’til 60C off 100 sec on ’til 160C off forever Oops – can barely see the “soak” time – let’s tweak some more: What if we at least flatten out the curve some by turning power off at – I dunno – maybe 100C? and turning it back on maybe 30 sec later? I guess I can make use of that AC controller after all. We’re really shorting the soak region, and we can’t make the sharp spike up to reflow. ![]() Using “whatever the hot plate will do” as the ramp up rate, a more appropriate picture would move the the profile line starting at the beginning of the soak phase: OK – the rate of initial ramp up to the soak plateau isn’t too critical, and the 2C/sec rate shown is sort of an upper limit. Guess I should have believed the bit about “The first step…”. And it never ramps up faster than the profile, so the AC controller isn’t really needed. The raw hot plate hits pretty close to a couple of the profile points. Here’s the ramp-up part of what the thermocouple interface measured, along with a sort of typical profile: The first step is to see how that completely simplistic approach compares to a real profile. I assumed the hot plate was able to heat up considerably faster than the desired profile, so I hooked up a solid state relay I could turn on and off with an Arduino to control power to the hot plate. (Or at least know how far off from ideal we were.) Could it cause such soldering anomalies? Is it possible to sort this issue out with process adjustment (profile tweaking etc.)?īy the way, manual rework of this defect after reflow is extremely hard.While the first few reflow attempts using the “turn it on, wait ’til the solder is shiny, take the board off” approach have more or less worked, it would be nice to see if we can come closer to a proper time/temp reflow profile without too much trouble. No any soldering anomalies.Īccording to component manufacturer requirements components have to be soldered within one year after shipment. During soldering stage all solder flows to component�s lead leaving soldering evidence on PWB�s pad (please refer to the picture). PWB is thin (0.8mm) and evenly populated so there are no any temperature gradients across the PWB during heating. This problem has appeared at PWB populated mostly with simple chips and a few IC�s. Problem definition Poor soldering of thermistors with Ag/Pd terminationīackground Process: lead free reflow soldering Paste type: Multicore LF300, SAC305 Component type: 0805 chip thermistor, Ag/Pd termination PWB finish: immersion Ag Reflow profile: fits LF300 process window ![]()
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