How to Dry solder small FPC board connectors

The LCD connector.

These connectors are very small, having 0.5mm pitch. And you need good soldering hands to get it done.
This part becomes more hard as there is no option for reflow, and also if we make solder bridges, those can’t be removed, as trying to remove the excess solder will make the plastic melt around the specific pin and the connector will not connect that pin to the LCD again.
Below is my technique for soldering the above connector.


First step: Cut a thin strip from any sticker(DP sticker has lots of white area) and fix the connector in place with the sticker.


Second step: Apply a tiny(or tiniest) amount of flux(paste type) to the connectors.


Third step: Use preheated micro soldering iron. Tin the tip by solder, but wipe the solder, we don’t actually need any solder because that will cause solder bridges. Press each pin of the LCD connector from vertical position with the tip of the iron. The flux will be used and the tinning of the PCB will take the LCD connector’s pins towards it and that solder(PCB tinning) will function as the joiner.


Now you are done. Clean flux residuals with IPA/Kerosene if necessary.
Never use solder to join, if you use any small amount of solder, then probably you’ll get thing messed up and destroy the connector.


Drag soldering is good for ICs with strong pins, and it’s bad for ICs with thin pins and also for connectors like this. You need to solder each pin individually to avoid the risk of actually bending pins.





Soldering the chip

For any first timers that stumbled onto this post,the chip here refers to a 48 pin SSOP package with a 0.635mm(25mils) pin pitch.


Equipment Used:
1.Any cheaply available 1mm solder wire,(don’t recall the price,bought this last year)
2.Liquid Flux,I used a locally available liquid flux,its a pinkish liquid in an unmarked dropper bottle.
(A 30ml bottle cost me Rs.10)
3.A chisel tip and a sharp pin like tip for your iron,(Soldron tips cost me around Rs.40 per tip,a few months ago.)
4.The soldering iron itself.Many claim that cheap 25-30W irons that connect directly to your AC mains supply wouldn’t be used for SMD work,but that is all I had around,so that is what I used.It is a 25W one from Soldron,the most common one you’ll see in India.
5.Solder wick(Rs.10 for a 1m roll)
6.Patience,which is extremely critical for this number of pins and fine pitch we are working with here.


1.Flux the pads.

2.Use a chisel tipped soldering iron and ‘relay’ solder onto it.What I mean is,no applying solder directly to the pads,rather melt some solder onto the tip and then lightly pass the thick(relatively) tip lightly over 5-8 pins,applying solder this way.The ideal height would be where only the solder blob grazes the pins,getting consumed while you pass it over the pins.

3.After you’re done adding solder to the pads this way,align the chip and use some means to hold it in place while you solder the pins.Many people use Kapton Tape,or let the viscous flux do that,but I just held it down with my index and forefinger.

4.While you make sure its aligned,come in with a sharp tipped iron and solder the 4 corner pins,in the order of top left,top right,bottom left and finally bottom right.When I write solder,I mean, NO SOLDER on the tip.Clean your tip and just touch the pins to melt the solder on the pads into a nice union of pin and pad.DO NOT keep your iron there for more than 2 seconds,or come in for consecutive ‘tacks’ on the same pin,doubting the joint or just wanting to make it look shinier(the pad(s) will overheat,and you will cause it to come off),you could wreck your PCB.Solder each of the 48 pins this way.

5.After you’ve patiently done one row of 24 pins,flip it around,do the other row and then test the pins’ joints by prodding them individually with sharp forceps(I use the kind used for dissection of lab animals).

In case you get solder bridges between pins (which you wont,if you follow the no-solder-on-tip-while-tacking-pins very strictly) use the solder-wick,but don’t keep your iron there for more than a second or two,since the tracks there will be fine,and can come off.That is how I made those 2 mistakes earlier.
 © 2014