Exceptionally his article will not be about MSP430, but about soldering.
Since we sell LCDs with fine pitch connectors, I get a lot of feedback of
people who get in trouble soldering small components like flat cable
(FPC) connectors.
I have been thinking about describing my method for a while, but you
know how it goes with ideas, especially the time from the idea to its
realization...
So let's try to put one connector on a PCB. I will use the smallest pitch
and longest connector I have (32-pins @ 0.5mm pitch). If you manage
with this one, you can rule the planet.
I am starting to sell a new LCD kit. Here it is:
As you can see, the LCD kit comprises one LCD, one adapter board
(pitch = 2.54), 12 chip capacitors and 2 jumpers (0 ohm resistors).
I will explain how I deal with the connector which is the most tricky part.
But when you are used to do it, it is easy. Don't abuse of coffee or
tobacco, and things should go smoothly.
Basically the most tricky is to put the connector at the right place +/-
0.05 mm. if you are less accurate, you increase the risk of solder bridge.
Before starting, one advice, by experience: do not use a too small iron.
I use this one:
As you can see, the extremity is at least 5-pitch wide (about 2.5, 3mm).
My experience with smaller irons is that they get cold when entering
in contact with the soldering alloy, with the component or the PCB.
Anyway there is no iron of my knowledge with a 0.3 mm end.
1. Pin coating
Coat a few pins at one end of the connector. This image tells you all:
It's not easy to make it apparent on a picture. As you can see, only the
4 last pins are not yellow. You can do this cleanly even with a big iron.
2. PCB coating
Do the same on the PCB. The following photos shows you that there
is more soldering alloy on the 4 last pins.
3. Connector positioning
Position the connector on the board. That's the most tricky part of
this operation. I use this lens:
Once the connector has a fairly good position, hold it firmly with your
finger, make sure it doesn't slip and press the iron on the few last pins
that you have coated. It shoulld be in the proper position now. The
following image shows what you should observe. The placement is not
perfect (the pns are about0.03 ~ 0.05mm to the left), but let's consider
that if the pin does not cross the pad border, you're safe. If it slips, since
you have soldered 3,4 pins only, you can still move it. Redo as many
times as you don't get a satisfactory placement.
4. Pads soldering
Now if it is properly soldered, you can fix the two big pads that hold the
connector mechanically on the board. Start with the opposite side. This
allows you to correct a small angular misplacement. Then solder the
second big pad.
5. Drown the pins in soldering alloy
Now the connector is in place and firmly held, you can solder the other
pins. Don't do them one by one, that's almost impossible because the iron
is too big. Don't hesitate to put solder in excess as shown below. As the iron
is big, the alloy is extremly liquid and you can be sure you will get no dry
points. You get a huge bridge from pin 1 to pin 32. The following picture
shows this soldering bridge which is beautifully regular.
Here is a closeup that leaves no doubt that every pin has been wet with
the melt alloy.
6. Removing the excess
Now the last step: remove the extra alloy with a desoldering tape.
I use this one which I think does its job and is not overpriced.
The tricky part: don't remove too much alloy. After removing, there
should be no alloy between the pins, but a fair amount between the connector
and the PCB
The result should look like this:
By seeing this image, it is obvious that there is no bridge between the
pins, and that the pins are properly soldered to the PCB. So the key point
I think is to use a big enough iron.
7. Test
Now, I would recommend anyway to test the pins 2 by 2 to verify that
there is no short circuit. This is difficult, I hope you have a huge
20-cm lens with lighting otherwise it will be hard.
Then put a flat cable inside, and verify the contacts between the flat
cable and the places on the circuit that should be in contact with it.
And now you can use the display.
Have fun!
Pascal