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wpeF7.jpg (10009 bytes)wpeA.jpg (318311 bytes)

A SMD reflow oven built in under 30 minutes for about a fiver.

Update - I am currently evaluating this toaster oven from CPC for larger boards...

wpe5.jpg (37384 bytes)wpe3.jpg (40771 bytes) 5.49 from Sainsburys.

The horizontal toaster ovens more commonly used for SMT work just don't seem to exist in the UK.

 



wpe4.jpg (383881 bytes)Surprised to find some electronics inside for the timer - was expecting something more mechanical


wpe6.jpg (510712 bytes)wpeA.jpg (31011 bytes)Discard superfluous parts... A pop-up SMD toaster is a really BAD idea, unless you want to scavange parts from boards, in which case it might just work...

Beware of very sharp edges - This toaster viciously attacked me during dismantling. Bastard,



wpe7.jpg (407442 bytes)wpeB.jpg (115181 bytes) Small thermocouple fixed to centre of underside of aluminium .'oven tray' for approximating temperature,  and  variac for control.

Variac is overkill but I had it to hand. A suitably rated (~700W) triac type dimmer, e.g. stage/disco lighting dimmer, motor speed controller etc. would do just fine.

Watch out for the element wires bending upwards as they expand when hot - 240VAC and SMT boards are rarely a good mix. Not to mention probably flammable solder paste vapours.

Perforated thin aluminium sheet was the shield from an old CRT monitor. Not sure to what extent the holes help or hinder - probably help a bit with airflow.

Keep it thin so thermal mass is low, but not so thin it sags. About 1mm. Low thermal mass gives a fast heat/cool time. The complete soldering cycle from cold is <2 mins.  



wpeC.jpg (401956 bytes)wpeE.jpg (311180 bytes)The top and centre elements are used. No particular need to remove the bottom one, but it should be disconnected.

The lower wire toast guide was removed to allow the tray to sit flat.

 

wpeA.jpg (366648 bytes)This setting is known as WAAAY TOO HOT! (unless you want to make some toast).

But useful for quickly preheating the ali. plate. Watch for those bendy (live) bits.


wpeF.jpg (68534 bytes) Oven-ready : all pasted & placed - no need to be super-accurate on placing chip components as the paste will suck them onto the pads during reflow. Fine-pitch parts have a few pins tacked down to avoid slipping

Leaded paste of course - no point in risking the higher temps for that leadfree nonsense for prototypes.

 


wpe9.jpg (451268 bytes)Preheat to 150 deg, cook for about 1 min, then increase to about 230 til you see solder flowing, then turn off and allow to cool. Gentle blowing across board speeds cooldown.

 

 

 

 



wpe8.jpg (581522 bytes)Fresh out of the oven. mmmm tasty!

Didn't even melt the FFC connectors! (YMMV!)

 



wpeE.jpg (20238 bytes)A few shorted pins on the 0.5mm pitch packages, easily cleaned up with braid.


 

wpe9.jpg (245379 bytes)I used a plastic stencils from www.http://www.smtstencil.co.uk/.

Apertures for 0.5mm pitch looked a bit marginal, but actually seem to solder fine - I initially used a solid line along the pin row instead, which is why I get a few solder bridges. I tried the fully-cut stencil and all pins turned out fine (left)

More info on stencilling here.

 


wpeD.jpg (488284 bytes)When building several boards, sticking all the SMD strips to small bits of thin MDF with thin double-sided tape makes pick&place a LOT quicker & easier. By using seperate bits of MDF, you can put each one next to the PCB while placing then move the next one in, reducing the required reach.

Use a foot-operated vaccuum tool. Not those useless finger-operated pump things ( although these are useful donors for a homebrew vacuum pickup) - you need continuous vascuum flow to cope with leaky tips. Once you have continuous airflow, you can use standard stainless dispensing nozzles for pickup - no need for the little rubber sucky things for small parts.



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