by patc » Sun Feb 01, 2015 9:05 pm
I didn't intend to write a post about this intermediate step but I had such a hard time with it that I decided to share my experience. Someone will certainly come with a much better way but albeit hard, at least the method described here works.
Say you have a micro-server Parallella and you want to access the signals on the Samtec connectors, probably the easiest way is to directly solder wires on the pcb tracks. It worked fine but then I decided I prefered to have a couple of Samtec connectors.
I don't have a stencil, besides even if the components are glued on the pcb other side, I wouldn't want to get the board through a reflow cycle again, so I went with hand-soldering.
Before on a homemade daughter board, whenever I got a bridge between the connector contacts, I added a bit of solder, increased the iron heat and sucked it all with a desoldering braid. It worked great so I felt pretty confident it would be okay with the micro-server as well. Couldn't not have been more wrong, it took me some 8 hours to get those 2 connectors (kind of) properly soldered !
I guess when a bridge develops between a GND contact and one next to it, the GND plane dissipates the heat and if the bridge is too far below the connector, no matter what I tried I couldn't get rid of it. For 3 times I had to remove the connectors with a heat-gun (the connector is trashed of course).
Eventually I used a nail-like tip for the soldering iron and 0.2mm solder (not lead-free). Also a microscope comes very handy.
- remove the excess solder on the pcb connector contacts
- apply solder to every connector contacts and remove it with desoldering braid
- apply flux on both the pcb and connector contacts with a coton tip
- soldering iron set to 310C(Celsius) apply a little bit of solder one contact at a time without touching the contacts on either sides
- if a bridge develops, immediately change the iron tip to a wider one (~1mm) and set to 370C
- apply a little bit of solder to the iron tip and suck the bridge with desoldering braid
- when a row is done, heat every contact separately to let the solder spread (310C)
- if there is no solder joint contact/pcb, add a bit of solder
- check for bridges with an Ohmmeter
- finally glue the connector to the pcb
I use non lead-free solder because I find it easier to use. A fan is next to my desk to avoid breathing too much of the toxic smoke.
The iron is set to 310C because if it is too hot, the solder being very thin will melt by just getting close to the tip, however a physical contact is needed between connector contact/pcb track/iron/solder.
I glued the connector because the amount of solder per contact is very small and I'm not sure the bond is very strong.
Although this method works, it is very hard and I don't recommend it even to non-beginners. Do at your own risks.