[marksk]

i have a circuit i'd like to prototype. as i've never worked with smd chips, i don't know how to prototype with them. can someone with experience using them please point me in the right direction? one of the chips i'm looking to use is a 64 pin TQFP.

thanks!

 

[jcx]

at that high pin count/small lead spacing a professionally fabricated PCB is the only reallistic option

often the chip manufacturer will have a demo board at a reasonable price - and with required firmware/working demo code these usually are quite the bargin in terms of getting a project going

fortunantly you can get small lot prototypes very cheap today - US$ 50-200 will get you several boards from any of several vendors

http://www.expresspcb.com/

http://www.protoexpress.com/

http://www.pcbnet.com/

(the no solder mask, no plating really cheap boards may be too cheap for such demanding chip, I would spring for a liitle more, you're going to need a few US$100 in tools to solder that kind of chip reliably anyway)

 

[beerguy0]

Quote:

Originally Posted by marksk /img/forum/go_quote.gif i have a circuit i'd like to prototype. as i've never worked with smd chips, i don't know how to prototype with them. can someone with experience using them please point me in the right direction? one of the chips i'm looking to use is a 64 pin TQFP. thanks!

I do this for a living. The only way you're going to be able to work with a package like that is to have a PWB made. The pins are too small and close together to allow traditional "dead bug" techniques. (Mounting the device upside down and using discrete wires to make the connections). These high-density packages often require multi-layer PWBs to get the signals, power, and ground to the chip. Your best bet will be to layout a PWB and have one made. We have a PWB milling machine at work that lets us make a double-sided PWB from a Gerber file, which is typically how I would do something like this. Routing on only two layers would likely be very difficult, though. You would also want the PWB solder masked to help prevent solder bridging while soldering.

With no experience in SMD at all, you are at an extreme disadvantage. These parts are very delicate, and easily damaged. You would need a very fine soldering iron, and you'll have to use 30 AWG solid wire, which is prone to breaking. High magnification and plenty of light are also necessary.

I wouldn't say it's impossible, but with 15 years experience with SMD prototyping, I would go straight to a PWB. There are few companies that make SMD adapters, but these are typically only available in SOIC or PLCC package types.

Emulation Technology makes adapters for just about anything, but they are expen$ive. (I've bought adapters from them that cost over $1000 for certain packages). They have sockets you could wire-wrap to, but be prepared to shell out big bucks. A socket with wire-wrap terminals would let you mount the chip to Vector board.

http://www.emulation.com/catalog/off...ceptacles/qfp/

 

[_atari_]

Hi,

alternatively you can get DIP-Adapters. These are basically small PCBs that convert SMD layout to DIP layout. Sparkfun has some:
http://www.sparkfun.com/commerce/cat...s.php?cPath=20

But you will surely find other vendors with some smart googling.

Best Regards

_atari_

 

[Jambo]

Another option is to get some adaptors to expand the SMD out into normal pins. Check out http://www.winslowadaptics.com; they'll probably do something that will help.

Edit: Oops, slow typer!

 

[threepointone]

check this out:
http://techref.massmind.org/techref/...kjetresist.htm
http://www.cnczone.com/forums/showthread.php?t=30951

People are reliably getting 3mils with this method, which is enough for tqfp-64 or any smd chip for that matter. I'm actually working on this printer right now, and I'll make a post with my personal results later on.

Double-sided board alignment is probably doable if you have a very good alignment assembly. High pin count should not at all be a problem; in fact, an SMD PCB is probably easier to make than a thru-hole PCB since you wouldn't have to drill holes for each pin. The main difficulty with this method (or any other diy pcb method) is doing the vias--the best solution I've seen is to use bare solid wire and solder the two sides, which would be pretty time consuming, limits how small you can make the board (I'm pretty sure the vias a professional pcb manufacturer can go smaller than 30awg), and will not accurately model the parasitic inductance that you'll see in the production PCB (though that won't be a concern for your application)