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why do you say it's insane? most, if not all, board houses can handle that pitch. Soldering is best done via reflow - solder paste with an oven or hot air. You can also use a hot plate/skillet - see sparkfun.com for a description of that technique. I have heard of people using a regular soldering iron with paste. I'm not sure I'd try that myself but solder mask will prevent bridges.
For production, this is OK. I was talking about prototyping. For a small pin count like 44 pins, the least they could do was to make a PLCC in addition to LQFP.
Then what would you say about new philips LPC3180?
A good prototyping system i've started using 2 months ago to reduce my cost. That is schmartboard|ez (www.schmartboard.com). Although they made this system for soldering the chip on it ,but you can easily use adhesive method and reuse both of the chip and board (El cheapo!).
For production, this is OK. I was talking about prototyping. For a small pin count like 44 pins, the least they could do was to make a PLCC in addition to LQFP.
actually a hot plate or hot air works great for prototype boards. I've used hot air on that pitch part with no prob. You just have to be a little carefull and not slop the solder paste around. I also flux the chip leads though it's not absolutely necessary. Solder mask is a key part of the equation as the surface tension of the molten solder confined to the pads will cause the chip to align properly. it sometimes takes a little tap.
I've actually seen a picture - some one soldered small wires to the pads of a .5mm pitch chip. Not recommended. Wish I could have found the picture again.
Having multiple different packages is an expensive proposition for chip makers so they really try to keep the number low.
Has done prototyping of several .5 pitch chips and connectors with up to 80 pins, I do the PCBs myself with UV proces and solder by hand with a normal soldering iron (werrrry thin tip neede).
My experience is that you almost need some 5x to 10x magnification with a stereo microscope or simular. Use some flux, and then "thinplate" the pads before soldering in the circuit.
When doing the PCBs it helps to make the pads a bit more narow to get more space inbetween, also makes it a bit easier to solder.
0.5mm pitch isn't as scary as you think. I've soldered a few 0.5mm pitch IC's with a standard soldering iron (18W, with a 1mm tip) and normal solder, from a spool. Just make sure you use extra flux, this will help stop those troublesome solder bridges. Also, just run your iron across a row of pins, with solder, and most will be nicely soldered. Any bridges can be removed using solder wick and a light touch. I was amazed at how neat it looks, just by using extra flux (not just the core in my solder).
UV etching is more realiable/accurate than transfer PCB's. Although, I have seen PCB's made using the latter that have 12mil tracks and no faults. I've never done this process before, but I believe you get some pre-treated PCB material (FR4?) and 'expose' it to UV light through a clear print of your design (copper tracks/pads are black, everythgin else is clear') on OHP sheet. Where the UV shines, the etch resist thats already on your board is deactivated, but where you tracks are on your design, the UV light is blocked (by your print) and so, the etch resist is left on. Its then developed, and etched. Because you are using light, it can be VERY accurate. But, its too expensive for me, I just get them from Olimex.
Given the option, I nearly always go for the smallest package available. It sounds mad, but I always like my designs to be small, and I hate drilling (if I'm making the PCB myself) so SMT takes priority. It also looks cool to have a tiny chip with a zillion pins
See for your self, if you've got some scrap boards with chips on them (PC parts like soundcards, ram, graphics, mobo's etc..) and try and desolder them. Then you could try soldering them back on, it's how I learned.
Probably won't help, but you've helped me before, take care mate.
Yes I remember, I think it was LCD backlight project.
I did try the pre-sensitized boards once or twice but never got the result and my patience ran out. I tried to expose in sunlight. The instructions on the board were in Chineese so I couldnt get the timing right.
I will try these again.
Your idea of practicing on old PC cards sounds good. I have a heap of those lying around.
The etching is a bit tricky but when you have figure it out its not that big of a deal.
Im using a laser printer to make 2 OH films, if only one is used the blacknes gets to light and some parts migth get messed up during development.
Use some tejp to attache the two OH films, the registration must be perfect! Its also important that the toner always is on the side closest to the PCB, mirror the top side of the layout when printing.
Then do the UV exposure, make sure that the film is in contact with the PCB everywere. It helps to use thinner PCBs (0,8mm) as it is easier to flatten under preasure when doing the exposure. Normal 1,3mm PCB easy gets bent in corners/edges when cuting them and its har to straiten that out again.
During development the result seams to get better if the fine parts of the PCB is gently "brushed" with a fine brush during development to help the proces betwen the tracks.
Then do the etching as normal in a tank...
I have done several PCBs this way, the first time it takes some test PCBs to figure it all out but then you should be able to get a preaty god yield. In the ned all edges gets realy sharp, Im a bit amaced about the result mysel...
regards Me
Added after 8 minutes:
UV exposure does not neet to be that expensive, but I guess olimex gives a better result and about the same cost in the end (but then you need to wait)
I build a exposure box from 4 UV light tubes (5$ each) and an old scanner box. The PCB comes with positive photoresist on, you just taka of a protecting paper and expose them.
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