Solder small 0,7mm^2 connectors on tiny Bluetooth module - Page 1
Forum section: electronics / projects

author: JoGra
author_rank: Newbie
timestamp: September 18, 2013, 05:58:46 pm
content: Hello everyone and especially DaveI got a tiny Bluetooth module from china (which did't look so small on the pictures). I made a custom pcb with solderpads in the exact positions as a breakout board.My question is now how do i best solder the module onto the pcb? Drag soldering? I don't know if that works because the pcb doesn't have a solder mask.Tin the pads first and just heat it up? What size for tip of the soldering iron would you recommend?Just uploading picturesEdit: Why can't i include pictures from my Dropbox?

author: ablacon64
author_rank: Frequent Contributor
timestamp: September 18, 2013, 06:01:09 pm
content: Quote from: JoGra on September 18, 2013, 05:58:46 pmI think it's the best option since it lacks solder mask.

author: RossK
author_rank: Contributor
timestamp: September 19, 2013, 01:07:56 am
content: Cant say i've tired this myself but i here's where i would start: tin the pads first - then remove the tinning with desolder braid so the surface is both tinned and level. next use a small dab of solder on the tip of the iron for good thermal contact then heat the pad+board edge with the iron and feed the solder into the small board edge cup. this will let the flux core fume where you need it and it should make for a good contact. when your done you should be able to use a multi-meter to test for any bridged leads.Good Luck

author: Psi
author_rank: Super Contributor
timestamp: September 19, 2013, 01:32:07 am
content: Quote from: RossK on September 19, 2013, 01:07:56 am+1Good braid will remove any bridges instantly.I would put a bit of solder on all the module pins and on the pcb pads then use the solder braid to clean the solder off the pcb (so the module will sit flat).Apply the iron (small tip) and solder each one at a time.Basically the same as RossK above.Its much easier when you already have a little solder on the parts (silver vs copper colored)Well done on the PCB by the way. Getting thin traces can be quite hard and yours look perfect.

author: ovnr
author_rank: Frequent Contributor
timestamp: September 19, 2013, 01:54:40 am
content: Rule #1 when it comes to soldering things that are a bit of a PITA: Use a ton of flux!On a slightly different topic: As I'm sure you've already seen, the annular rings on your capacitor pins are too small for the drill size you've used. You may want to consider upping that in the future, as the traces are almost broken by the drilled-out hole.

author: G7PSK
author_rank: Super Contributor
timestamp: September 19, 2013, 05:27:52 pm
content: I would tin all surfaces first, making sure that all tinning is levels as previously suggested, then I would flux the the boards and then use the iron to carry solder to the joints in turn.

author: JoGra
author_rank: Newbie
timestamp: September 19, 2013, 09:07:24 pm
content: Thank you for your helpful posts.Did it like that now:I tinned the pads at first, but just thin. The placed the module correctly and used my huge 2,4 flat tip to fix in place.The tip covered two pads and with just a little more solder i could solder the pad just as fine. It worked perfectly easy, no shortcutsHow bad is it to leave the copper traces unprotected? should i coat them?QuoteIt took some work to figure it outBut the important things were:- Use an inkjet printer with a fine resolution and the appropriate overhead transparency. I could directly use the print, it was perfectly black and dense.- Find the right exposure time for the UV-Light, for me it was 2min. Don't have any space between the transparency and your pcb- Use HCL (~30%) , H2O2 (~30%)with the proportions 1/1/~0,6 for HCL/Water/H2O2 i got that fine result after one or two minuets in the acid. First the Water then the Acid....