Tips for soldering link wires to fine pitch components... - Page 1
Forum section: electronics / general

author: David
author_rank: Frequent Contributor
timestamp: December 12, 2010, 09:24:42 pm
content: Hi all,I need to do some modifications to a PCB which involves soldering some wire-wrap wire (Kynar etc...) to a TSSOP 0.5mm pitch IC. I can't bridge the joint with any of the neighbouring pins so it's going to have to be directly soldered to the pin (also no vias...). Any tips on how to approach this/iron tip to use?Regards,Dave

author: Balaur
author_rank: Unknown
timestamp: December 12, 2010, 09:45:37 pm
content: Flux. Lots and lots of flux.- put a dash of gel flux on the pin and its surroundings- use leaded solder- curse the ROHS directive and how the bureaucrats sucked all pleasure from soldering. Mourn for the days when sun was young and the solder was shiny- use a chisel (screwdriver?) tip. I prefer a 0.03"/0.8mm but a standard 0.05"/1.2mm should also work nicely- wet the tip with some solder- place the wire on the pin, aligning the tip of pin with the tip of the wire. The wire should go over the IC and not in the continuation of the pin. Some wire bending is required to allow the wire to follow pin shape. The "over the IC wire" is just a personal preference, allowing the soldering tip to have some free action field. Feel free to try whatever you like- place the soldering tip next/over to the pin and wire. Don't worry to much if the soldering tip is too wide- wait for the solder on the pin to melt and hopefully for some of the solder on the soldering tip to migrate between the pin and the wire- watch in wonder how the flux manages to keep the neighboring pins nicely separated

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 12, 2010, 11:26:07 pm
content: As above, but pre-tin the wire first.Oh, and more flux, fresh flux - after any failed attempts, clean off and add new flux.

author: Unknown
author_rank: Unknown
timestamp: December 13, 2010, 12:44:29 am
content: Also be careful not to melt any nearby components like capacitors and connectors. I frequently fall for that it's not funny!A very clean tip is critical and fine tips oxidise quickly if left with no solder. Use a temperature of 320 degC with lead-free solder if the product is to remain compliant. You dont need to feed solder directly into the joint, the amount on the tip (as per Balaur) will do fine.Clean with isopropyl alcohol or fluxremover and inspect with a magnifying glass for wire strands or solder splashes between the TSSOP legs.Flux is your friend!

author: osmosis321
author_rank: Regular Contributor
timestamp: December 13, 2010, 05:42:20 am
content: It's not all that hard with a bit of finesse. Although I won't disparage the tips offered by others, I will suggest that it needn't be that big a deal.What you need most is a steady hand. Step away from the coffee.1) Tin the tip of the wire.2) Apply a small amount of flux to the IC pin and lay the wire on top.3) Press the soldering tip on it momentarily.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 13, 2010, 11:03:43 am
content: Another point is that kynar wire is often slightly more than 0.5mm thick, which is a problem if you need to connect to multiple adjacent pins. It can be thinned slightly by stretching between a couple of pairs of pliers.Stretching also hardens the copper, making it stay more straight, which can help during positioning.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: December 13, 2010, 10:35:30 pm
content: Lots of flux, and make sure it is real Kynar (or any PVDF insulation), as otherwise you'll end up melting the insulation further and further down.I have found giving the end of the wire a little squeeze between some pliers to flatten it out sometimes helps. Also, if it's really awkward, a bit of kapton tape with a slit cut in it can hold the wire and stop the solder leaking out.