Perhaps the biggest obstacle facing low volume/DIY users of the Motorola ColdFire family of parts in soldering the processor to a prototype PCB. In April 98 I asked this question on the ColdFire Mailing List:
Does anyone have any good advice on how to stick down big SMD devices in a DIY/low volume environment... I used to be up to production quality through-hole assembly but I went to college and kinda missed out on the transition to SMD.... - David Fiddes[D.J@fiddes.surfaid.org]
There then ensued a torrent of useful advice. I'm not going to try to paraphrase or rewrite anthing incase I muck up the basic meaning. Here is a transcript of the discussion:
This technique was suggested by Paul Breed and is very similar to commercial hot air stations...but at a fraction of the price!
With about $200.00 of the proper tools I now believe that SMT is easier to prototype with than the old holes. The tools are: Weller Pyropen $100.00 Small tube of SMT solder paste. $20 wooden Tooth picks and razor knife, and potters clay Magnifiying Glass with built in light $60.00 Small hand operated Suction pen. $20.00 The outline of the process is.... WARNING I HAVE NOT PERSONALLY USED THIS PROCESS FOR PARTS BIGGGER THAN ~68 PINS I have used it on fine pitch parts. 1)Using a toothpick and Magnifiying glass dab a small amount solder paste on each PCB pad. 2)Using the small suction pen and the magnifying glass place the part. (BE very careful handling the part, if you bend any of the leads you are toast) If you did not use too much solder paste on the pads perfect alignment is not necessary, as the surface tension of the melted solder will align the part. 3)If there are nearby parts you don't want to heat put a clay barier between them and the part you are adding. 4)Fire up the Pyropen with the hot air tip. (The cool thing about this is that the gas comming out of the pyropen has burned so it is oxygen depleeted and you don't need to use inert gasses like the "professional" hot air stations.) Point the hot air at the pins of the device.... run down all all of pins at a steady even pace...... Then your done...... 5)If you need to remove the part heat up the pins and lift with the suction pen...or pry at the corners with the tooth pick You will probably destroy the part is it has lots of pins...... but the PCB should be fine... just clean up the pads with some solder wick. Go to your junk box..... find an old PC card that you are not using..... Practice taking the parts on/off Start with the R's and C's workup to the monsters.... Good luck... It is fun! Paul
This technique was suggested by Leslie Mable and whilst it looks a little harder to do than Method 1, doesn't require much in the way of extra tools.
I worked with low volume SMD parts for a few years. The method I adopted works well down to 0.5mm pitch (and that's quie a lot less than the 0.65mm of the 5206 when soldering by hand). Get a fine-ish soldering iron (no need for a point - 1mm diameter on the end will work fine). Solder - 22 guage (I don't know what our American cousins would call this - it's 0.023inches diameter), and some solder wick - pre-fluxed. Solder the chip to the board on all sides - alignment is important - but don't worry about shorts - I generally solder the pins with generous amounts of solder into clumps of 5 to 10. This helps ensure that the solder gets to whet all of the joints. Then using the solder wick, with the wick between the iron and the pins, allow all the excess to be drawn up from the pins. You will have to keep trimming the wick after every twenty pins or so. The flux from the braid helps maintain the surface tension in the molten solder, and with a little practice it is possible to obtain a finish which (after cleaning) is indestinguishable from a mass produced, flow soldered product. Some people may be tempted to use a solder sucker to remove the excess. This should be avoided, since the mechanical shock, combined with the heat may cause the fine surface mount pads to separate from the PCB laminate. After soldering, you should remove the remaining flux with a suitable (environmentally friendly) solvent, and then inspect thoroughly for shorts with a lens and with an ohm meter. To avoid any risk to the devices on the board, use one which can only generate a low voltage. This method will work on PCBs without a solder mask layer, perhaps for a prototype, but its better to have one if the budget will stretch.
This is perhaps the easiest way to solder SMT devices although it might make a bigger dent in your wallet! Ian Caddy at SystemCORP suggested this:
Something that we do when prototyping small quantities of high desity SMD part is to take them to a small to medium assembly house and ask them to put on the high desity part for us. These places normally have a very good rework station and their charges are reasonable, in Australia about $25 AUD per hour and they normally only take about 5-10 minutes to do a part. The other way they can do it if you haven't placed any other components on the board is they may reflow it. Just manually put on the paste and place the part, then in the oven and its done. I am sure there should be small companies around that are able to do this sort of prototype work for you.
Whilst not strictly a way of soldering down SMT devices using prebuilt PCB headers
allows you to prototype your design using wire-wrap or similar with considerable cost saving
over a PCB. MiKe
> Some time ago, I have seen ads for adapters with a fine pitch SMD > solder area on one side and wire wrap pins on the other side. You > have to solder the chip yourself, which may be tricky, but you only > have that problem once because the whole assembly can then go on a > standard PGA ZIF socket, or you can use it directly with wire-wrap or > DigiKey Catalog (www.digikey.com) has these adapters. I just ordered a 208-pin QFP to PGA adapter for the Coldfire 5307. I don't actually know of a ZIF PGA Socket that is 17x17 and has 208 pins, but I do know where to get wire-wrapping extension pins.
Stefan Wimmer recently suggested this:
A pack of 5 PQFP100 adapters was in the ballpark of $12 IIRC. > What is the address and > phone number of the company that sells these adaptors? In CF-Digest #180 I published their address: Wainwright Mini-Mount-System GmbH Hartstr. 28C D-82346 Andechs-Frieding Tel: +49-(0)8152-3162 Fax: +49-(0)8152-40525 They're building a web page at the moment and I'll tell here about the when and where as soon as I know.
You can see these devices in action on Stefan's web site where he is developing a multipurpose SBC based on the Motorola MCF5307 processor