Re: gEDA-user: Soldering fine pitch chips

[Xtian Xultz <xultz@xxxxxxxxxxxx>]

Em Sex 10 Mar 2006 05:41, Karel Kulhavy escreveu:
> I once replaced a 1.27mm SMD chip on a motherboard and had only
> transformer soldering gun. So I cut a piece of copper tin with a hole
> in the middle. I made sure that the long edge is straight. Then I
> bolted the tin to the loop of the transformer gun and used it to heat
> all pins on one side at a time. It was easy to solder and desolder.
> After rinsing with isopropanol the soldering looked like from a factory.
>
> Do you think this method could be used to solder down fined pitch chips
> like 1mm 0.7mm or whatever is common today?
>
> CL<

I designed a board with an LPC2106 wich have 20 mils from pin to pin. As my 
fab is not good enough, the pads have only 10mils with 10 mils spacing. The 
best would be the pad having 12 mils with 8 mils spacing, but probably I 
would have a lot of short circuits in the board. 
I have only a solder iron to mount 40 boards right now. Its not easy, to 
everybody its a scary situation, but I my boards are working.
To do it, I made something really simple. First, I place the chip on the 
board. Thats the worst part, all the pins must fit exactly over the pad. The 
I place some solder over some pins, and its not important if some pins become 
shorted with solder, its normal. So, I have the part firmly attached over the 
pads. If not, I must correct it right now before doing the next step.
Then, the solder part. I made a ball of solder over some pads in one edge of 
the component. That must be done quickly to not damage the component. Then, I 
put the board in the vertical position (but not completely vertical), and 
make the ball of solder to walk over the pins, from top to bottom of the 
component. When I am in luck, the ball solder all the pins, and get out of 
the component, placing in the point of the soldering iron. With 50 mils 
components, I allways can, its really easy to solder. With that crap 
footprint of 20 mils, I can do it in 30 to 40% of the times. If a short stays 
on the pins, I remove it with dessoldering shield. 
I made it on the four sides of the component, and tada! My microcontroller is 
on the board, ready to run.

Hope I helped.