Soldering of FPGAs

It is perfectly possible to solder and unsolder FPGAs (up to PQ208 or similar) with fairly simple tools - good soldering iron, solder wick, and, with my eyesight, a low power microscope. You can remove an fpga with a very sharp scalpel blade (you will probably destroy the fpga in the process).

The real problem with FPGAs is the PCB. Most FPGAs are very high speed devices and need a good ground plane and proper supply decoupling - without these you will have endless problems. You should also bear in mind that typical pin spacing is 0.65mm - translated this means 'very close' and very fragile. It is very difficult to reliably attach wires directly to a device. Making your own PCB for these purposes is not a job to be undertaken lightly, particularly as you usually need at least 4 layers !

So, my advice would be - if you are learning, and do not have a specific project in mind, buy one of the development/educational boards - believe me, the reduction in hassle is well worth the extra cost ! There is also great merit in starting from a known working state - debugging an FPGA board may take more exotic equipment than you have hanging around. I have used Burched boards

, but there are quite a few others. When you have a specific project in mind, and a bit more experience, then design your own pcb - and find someone to make it for you.

Dave

possible for a

Hey Joel,

It is possible to solder TQFP/PQFP packages using a gold soldering iron and bit of patience. Be sure do doulbe-check visually and electrically the board before power-up.

There are also other methods. For example, take a look at this page (I have not tried this method myself... yet):

Regards,

-- Georgi

possible for a

Your advice is perfectly ok, let me tell you though, that I'm regularly fabricating my own four layer PCB's at home. To produce a four layer PCB 3x3" in size takes about 4 hours. Such a PCB costs me then ~$10 so provided you need some of them over time it's IMHO well worth the effort. That's especially true for prototyping and advanced hobbyist use. My main motivation was that I really got sick of waiting for the boardhouse to complete the PCB. I know that in some areas it's much easier to get cheap and quick PCB's, but four hours are IMHO hard to beat! :-)) If you consider the fact that where I live getting a four layer PCB of said size in say three workign days costs a fortune ($2K!!!!) it really makes sense.

Six layer is also possible just means more work (add two hours for above sample PCB). So, if one is dedicated enough it can be done. The main requirement is having a through hole plating station. I built one myself. Those which are interested might want to visit

Soldering BGA's is trickey but even here are (rare) "homebrew" solutions around. I'm curently experimenting in this area and hope to have this working for myself soon.

Please note that this is strictly for my personal needs / prototyping work. That said it's clear that even for small production runs I'm more than happy to use the services of a board house.

Markus

Joel, It is possible, but not advisable. The finer the pin, the lower the total heat time is. Also the probability of solder balls and shorts is greater. Certain vendors sell development boards with mounted FPGA's pinned out to berg connectors and some to MIC connectors. It's safer this way and less agravation, also it addresses noise and power decoupling issues.

Soldering by hand works. Investment in micro-width solder and solder-wick are only part of the journey. I can do this kind of work easily under a stereo microscope but I imagine a hobbyist may not have one handy and they tend to be more than $100-$250. Perhaps jewelers' magnifiers (the glasses with the lenses on swing-in arms) could suffice but personally, I don't want to get my face too close to boiling rosin.

Tacking down opposite corner pins for an alignment check around all four sides is a good start, allowing a slight skew to be corrected before going too far down a wrong path. With those corners in place, the trick is to get good solder flow without wicking to the adjacent pad. It's tough but can be fun.

and

board

have

development

The easiest part to solder is a BGA. You line it up on the pads and to keep it from sliding during reflow you must glue some sort of "corral" around it; I've used SMT resistors for this. Then you just heat it up with one of those big red hot air guns that look like oversized hair dryers that would fry a hole in your scalp (I think these are around $100.) I've done this with success. You may have to put solder or paste on the pads if there is none on the PCB already.

-Kevin

possible for a

If you really want to solder a fine pitch IC - Get a Metcal soldering iron (or borrow one)

pinned

I found that soldering SMDs (including TQFPs and PQFPs) is easy, as long as you have flux handy. Tweezers and a magnifier can also be useful. Jean

more advices here:

possible for a

possible for a

The method I used to do for PQ208s and such was to make my PCBs with lead&tin coating. Now, all what I needed to do was to glue the PQ208 part in its place, and use hot air on the pins. Less than 2 minutes for a perfect job.

If you keep an eye on auctions you might be able to pick one up for this sort of money.

An example is

Nial

------------------------------------------------ Nial Stewart Developments Ltd FPGA and High Speed Digital Design

in

thats a good idea!

Just for reference...

It may not be too expensive to have a 4 layer board made commercially.

I've used PCB Express -

There are several similar sites. 4 boards, 20 sq inches, 4 layers, no silk screen or solder mask is $183. $274 gets top side screen/mask. $45 more for bottom.

They are non-fancy design rules: 7/7. That's probably good enough for hobby type projects.

You do need access to board design tools and how to use them.

Then you still have the problem that started this thread.

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Yes. You'd better have pretty good eyes and steady hands.

I am currently installing Xilinx XCS30TQ144 chips on a small production product, that is the .5 mm lead pitch package. I use solder paste, which I got in a 35 gm syringe. You will need to beg, borrow or steal (just kidding) needles around

20 gauge. I cut them off fairly short, and then round the end off on a sharpening stone so it is relatively free of scratchy edges and has a 30 degree or so slant on the end. You place the thinnest bead of solder paste on the outer edge of the solder pads on the PCB. You then position the chip with angled tweezers and solder one corner lead, while trying to align the chip as well as possible with the pads. You go to the opposite corner and do another. If necessary, you may have to walk the chip slightly into better alignment. When you have all the pins reasonably well aligned, you just wipe the soldering tip along the rows of pins, and the solder will flow into the joints. If you use too much solder, you will get bridges. These are removed with solder wick. When you get it all soldered, apply rubbing alcohol to the chip and surrounding area, then scrub very gently around the leads with a sift bristle toothbrush for a few seconds. Wash in water, then hit it with the blast from the kitchen spray nozzle. I then violently shake the board to drive off excess water.

The soldering iron should have temperature control, and a very small pointed tip. I use either a Weller 1302 (old one) or the WSL with WMP iron (current model).

Ahh, it is VERY difficult to REMOVE such chips with simple irons, etc. It can be done, but is very time consuming. On the other hand, the $40 package-specific desoldering heads can be adapted to some standard irons to get a specific chip off cleanly.

If you don't want to save the chip, but the board, you can cut the leads off with an x-acto knife, use tweezers to remove the leads, then desoldering braid to clean up. You can also use braid to remove the solder, then lift each lead one at a time, but that is really slow.

Jon

Hey, I'd really like to hear about your multilayer process! I have the gear for 2-layer, but often just have them done by commercial shops. But, I could be real interested in any innnovative laminating and plating processes you use!

Jon

Hi Jon

I recommend you then to join the

group. There I posted the steps involved some weeks ago (search the archives). Besides, the group is really a very good place to start.

If you have a trhough plating station (that's what I asume you mean with "I have the gear for 2-layer") then you are basically all set. If you don't have a trhough plating station then you definately will need one.

Markus

I assume you mean 208 pin and 240 pin QFPs. Use lots of flux and have some solder wick on hand. I don't use a needle tip, the 1/16" tip works just fine. The pins/pads pull solder off the tip and I add solder to the tip (not the pins) as I go along.

The trick is to touch one pad at once so as to avoid bridging. With some practice, you'll see which way surface tension wants to pull the solder and how to get the solder to flow onto the pins. The sizzling of the flux helps solder flow and gives you audible feedback.

I've just treated myself to a used Metcal SSTS soldering station with a selection of new tips. The 'mini hoof' tip I got is designed for drag soldering and works very well on 0.5 mm spacing leads. With care (it takes a bit of practice) there are very few solder bridges and the joints need little or no resoldering. Metcal has some useful application notes on soldering and desoldering techniques for different packages.

I'm now looking for an affordable stereo microscope.

Leon

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