Quote:
Originally Posted by davidfor
I'll have to see how hard it is to do a transplant.
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eBay has loads of cheap kits with SMD chips. Like FM Radio with a TRF AM.
Practice.
You can also practice with cheap pack of SMD resistors between tracks on strip board.
A 2mm to 3mm flat tip and 30W or more iron is good. Not enough heat on fine tips.
A tiny spot of glue can help.
Also make sure you pre-tin the SMD chips (except ICs) and have NO solder on bit, but it's wiped on a wet sponge.
Trick for SMD ICs: Pre-tin PCB, but no bumps, use fluxed braid if there are shorts or excess. Line up IC and reflow diagonal corners. Then simply press down on all the leads. Doesn't matter if you are soldering 3 or 4 leads at once as long as there was no excess solder.
A pre-heat with a commercial PCB heat gun and fine nozzle helps remove. Never use a Solder Sucker plunger tool except on old vintage tag strips. Use fluxed copper braid to remove solder. SMD/SMT is actually easier to rework than Plated through hole, except for BGA and other parts with connections under the package. They need specialist gear. I simply cut off faulty SMD ICs at the body and then braid to remove debris of leads.
Polarity of the LEDs is important! You can use 3V (2 x AA cells) and a 220 to 1000 Ohm series resistor to check.
Some fine pointed cheap tweezers in bargain cosmetic packs are good for SMD.
I've been doing SMD soldering for over 20 years and I'd not attempt this. Translucent coloured lacquer / nail varnish or a coloured plastic film would be my approach. I'd test with a standalone LED. Bare LEDs ALWAYS need a series resistor.
I got a new kettle and was disappointed that the power switch is illuminated by a too bright so called "White" LED (which must be interesting to power from 230V AC) instead of a neon. A Neon only needs a resistor (about 100K to 220K on 110/120V AC or 220K to 560K on 220/240V AC). They are very long life.
White LEDs don't exist. They are Blue to Violet to near UV with a yellow phosphor. The phosphor wears with age and the light gets bluer/purplely.
RGB LEDs are only use for novelties, indicators or backlights as the spectrum is a narrow red, blue and green spike. Many don't mix the colours well as all are three chips in one package, they also need more than 2 pins unless the red & green are in series and the blue in parallel in reverse, then AC drive can give yellow, blue, simulated white and other shades (but no red, orange, green or cyan)