Jump to content

- - - - -

Cheap/Easy homemade SMD-to-DIP adapters

  • Please log in to reply
8 replies to this topic

#1 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 09 August 2010 - 01:28 AM

Disclaimer: I've been meaning to write this up for ages, but I've discovered that the manufacturers of PMC (Polymer Modeling Clay) recently changed their formulations lately, due to current and possible future European regulations (as well as an, IMHO, complete misapprehension of what the market wanted. I now need to do some tests to see what brands and oven profiles work for standards solder paste today. I'm posting this now in the hopes of motivating myself to actually perform those cheap and simple tests.

Back in the day, integrated circuit chips and many other components almost always came in DIP (double inline pole) packages or maybe SIPs (half a DIP, with a single row of pins. These were very convenient for the home tinkerer: the through-hole pins, with their 1/10" (2.5mm) spacing allowed for compact designs, but left enough room for easy home printed circuit layout and manufacture. With a little care, you could even run a signal trace *between* two pins (very helpful when trying to get from pin A on one chip to Pin B on another, when there were several chips on a board. Perhaps more importantly, you could plug them directly into a prototype board, along with your other (leaded) components and a few bits of wire, and prototype an entire working circuit in minutes.

a1.jpg a2.jpg

If you wanted to do SMT (Surface Mount Technology, where the components sit flat on the PCB, instead of poking through drilled holes), you could easily bend the pins flat so the devices sat flush on the board. However, as time went on, SMD became so common in industry that a lot of the newer chips were never made in DIP packages. They were made in flat formats with much tinier pins and pin spacings, often under 1 mm. This was bad enough, when you consider that most hobbyists (and techs) used 24-28 gauge wire (.5mm-.32mm diam) to wire their circuits, but Many SMD chips don't have pins at all, only pads. Even if you were willing and able to solder wires to the individual pins/pads, it was painstaking and not always practical

a1.jpg a2.jpg

Sure, you can buy all sorts of sockets, adapters and breakout boards (small PC boards that have aa place to solder the SND chip of your desire, and either pins or solderable wire holes to allow you to "break out" the pins to your desired format), but aside from the cost (typically starting at $3 each, today) there are so many SMD chip packages that you never seem to have the one you need on hand, which puts you on hold for a week to order them

Most often, I bit the bullet and made whole sheets of breakout boards myself. I'd lay it out in a graphics or PCB program, print it to acetate, clean a whole copperclad sheet, spray it with photosensitive resist, sandwich it with the acetate in a picture fame, and expose the whole mess to UV (sunlight works) for several minutes, then "develop" them with a special solution, etch them with somewhat caustic chemicals, and dissolve the remaining resist (or leave it to protect the copper until use) then carefully cut them apart. Today many people use a slightly simpler (but to me, much more tedious) laser printer method.

It's really not bad, once you get used to it, but it does take time, and I'd often spread it out over several days. I'd make 100 photo sensitive boards in 1-2 hours one day, and carefully store them. When I needed a new breakout board, I'd do the layout; print the acetate; expose, grab a presensitized board, expose, develop, etch and cut it -- it was a lot of yak-shaving (an entire project you *needed* to do before you could do the project you *wanted* to do), but since I could make 25-100 breakout boards on a single sheet, as easily as I could make one, it was only a pain one every few years, for a given SMD package.

Still, each time I had to make a batch of breakouts for a new SMD package type, I felt here had to be a better way. And there is. I went back to a method I developed in grade school, when I was first learning to etch DIP PC Boards I'd painstakingly drawn on copper boards with an ultrafine Sharpie pen, and/or rub-on transfers (and which often contained mistakes).

Basically, you make your own adapters from modeling clay (I use polymer modeling clay). It takes mere minutes (plus 30-60 minutes unattended in a toaster oven)

In the almost 40 years since I came up with this method, I've never seen it described anywhere on the web, so I guess this is a world premiere. That's kind of shocking.

Hide: This space to be updated with materials tests/reviews

#2 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 09 August 2010 - 04:26 AM

CLAY (I use polymer modeling clay [PMC])
SMD CHIP of the type you will be adapting (as a template)
WIRE of suitable diameter for the pins/pads of the chip
RAZOR: X-acto-style or plastic disposable hobby razor
piece of 1/4-1/2" wood (separable square chopsticks, a paint paddle)
Solder (I like soldering paste, but you could do it with wire solder)
Soldering iron or hot-air pen (optional, if you have a hobby toaster oven)
oven/toaster oven (you can use your kitchen oven, if you must)

If you do electronics, you already have all of these except the clay, and that's just $1-2.

[The first batch of PMCs I tested, slightly obscured in polyethylene bags to prevent drying]

PMC is basically a reusable (until baked) 'clay' of powdered PVC (PolyVinyl Chloride -- a common plastic often used in toys and home plumbing) plus  volatile oil/plasticizers. When baked at a low temperature (typically <300F = <150C), the plasticizer evaporates, and the plastic melds into a fairly rigid mass with almost no shrinkage.

The properties of a PVC can vary greatly depending on the polymerization length (number of PVC subunits in a chemical chain) and branching. PMCs made from these PVCs can vary based on solvents and plasticizers used, powder size, etc. as well as the temperature and length of baking. The one property that matters most to us is temperature tolerance, because we're going to have to briefly solder these (at ~183C = 361F, for regular solder). Since most PMCs are cured at 150C=300F for 1 hour or more, the few seconds of soldering shouldn't make much difference, but most hobbyists don't have precise control of their iron's temperature, so the tip of the iron may scorch or melt some PMCs, esp if not thoroughly baked. We'll also demonstrate a simpler "toaster oven" method

You may also try a lower melting solder like Twix™ (275F = 135C) or even Wood's metal (70C =158 F) which melts easily in boiling water! (is it any mystery why I love Wood's metal enough to make my own? It solves so many fabrication problems! Almost any material that can be left in a hot car in the summer can tolerate wood's metal, and it won't overheat chips)

PMC may not be the best material for this projects, but it is cheap, widely available, and comes in only a few international brands, while other types of bakable modeling clay can vary widely. If you have some other bakable clay on hand, go ahead and try it (report back!) Mineral clays might be better in many ways (stiffer and high-temp), but in my experience, many clays shrink 10% or more, which can be a killer. I may look into the nonshrinking "dimensional" clays used by architects and engineers.

For a device with up to 16 pins, a little shrinkage acceptable (you may have to slightly widen some of the pin-ways with a razor), but for a device with, say, 40 pins in a row, even the 1% shrinkage of PMC will lead to a .4 pin displacement at the far end: i.e. the farthest soldering contact may bridge pins 39&40 (and each pin before that will have a proportionately lesser alignment problem). If you center the device so the middle pins are exactly aligned, the pins on both ends will only have +/- .2 pin displacement, but even that won't help if the shrinkage is 2% or more (= almost one full pin displacement over 40 pins)

Now people get really scared by the word "plasticizers" these days, so I'll explain why I say it is safe to use your kitchen oven to do this (occasionally)

1) the mass of each adapter is tiny (the first test case below was 150 mg) and is only a 1-2 percent plasticizer (that's why they don't shrink when baked); of that only a small fraction could possibly of any health concern (the product is non-toxic, and though I wouldn't advise eating it, I'm sure most kids do, or at least don't wash it all off their hands)

2) The vast majority of those few milligrams will vent as vapor, any trace that is left in your oven will primarily be on the heating elements and walls, not surfaces you cook on,

3) these volatile organics evaporate or oxidize with heat and time, so any trace left behind will be 99% gone the next time you use your oven

4) I'm not responsible if you turn yourself or your family into androgynous mutant sludge monsters. Read the disclaimer that covers the entire forum. I think it's safe enough for me, but only you can decide if its safe enough for you. If not, hey, a cheap toaster oven is just $20 (and can be used for other potentially toxic tinker tasks) so you have only yourself to blame if you cheap out and don't buy one for you tinkering. You can also use

5) if you're still nervous, use a mineral/earth clay. I can't guarantee they're any safer. After all, the FDA advises against taking dolomite (mineral) supplements because they may have trace natural lead and other metals in with the good stuff. Heck, food, drink, sex and air can be dangerous. What does that tell you about the world we live in?

Sheesh! That was a lot of background. (but if you didn't read it up front, you never would)

Next: the ridiculously simple method

#3 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 12 August 2010 - 02:34 AM

Step I: Taking an impression

I like to work in amounts of 2.5-2.8g.  It doesn't matter if you don't have a scale that will reliably measures in the 0.1g or lower range. There's nothing magic about this number. It's just the size that I started doing this kind of micro-impressioning in. It happens to be the mass of a block the exact size and shape of a Scrabble™ tile. (In fact, at one point, stuck in a VT cabin with an incomplete Scrabble™ set, I made a whole set of tiles out of PMC. It can be a little dangerous to be around me when I'm bored.) It also makes an oblong about the size and shape of a peanut M&M, and is about 1/20th of a standard 2 oz (58g) PMC block.

My first example will be an adapter for a 14 pin SSOP-narrow chip (SSOP-narrow is just one of many SMD form factors) 2.5g of PMC should easily produce 12 or more finished adapters of this size, but aim for 10 (it's a pain to try to use the last bit. Save it for your next batch.) A single $1-2 block of PMC will make hundreds of adapters (depending on size)!

Here are the dimensions of our first example:
Though you won't use these numbers directly, there are a few key dimensions to note:
a) the width of the pins (note the wide variance: this is why I try to take an impression of the exact kind of chip, from the same manufacturer, as I will be using in the circuit)
b) the gap between the pins (the PMC that oozes up through this gap will guide all our work)
c) the full outside distance, end-to-end and pin-tip to pin-tip
d) the center-to-center pin spacing on the datasheet for your particular manufacturer can be important because the same chip can be made in metric (.600mm) or English (0.250" = .635mm) spacing, and once you've made a batch of adapters, you'll want to buy the same spacing in the future. For short chips, like this one, an English spaced PCB or adapter will work with a metric chip, and vice versa, but longer chips may not work, because the .035mm difference in pin spacing, times the number of pins in a row, becomes a substantial fraction of the pin spacing, and the pins will bridge the pads or vice versa.

Note that .035mm is 35 microns (the width of five red blood cells), which is far smaller distinction than, say, a brain surgeon would trust themselves to do with their bare hands, you'll be amazed to find how much we can get away with, if we just lay our process out right

The first step is to condition the PMC. This basically means "squishing it until it is uniformly soft. I personally prefer to roll it into a ball, a 1:1 (length:width) cylinder and a penny-to-nickle sized disk, and repeat at least 10 times -- squishing, not folding.

I prefer to avoid folding it at this stage, because sometimes folds can produce weak seams that can split or crack later. PMC will pick up skin oils, any dust on your work surface, lint from you clothing ... anything, and this stuff can get in your way. You'll end up folding and merging loose bits plenty of times as you work, so why add inclusions now?

Uniformity and not softness is the most important quantity, and the clay usually needs a bit more squishing even after you *think* it's uniform. Softness is not a good guide; it depends on temperature, humidity, age, storage conditions (both before and after you buy it -- and you never know how it was stored at the factory, warehouse, in shipping, etc) Besides, too much softness and the accompanying stickiness isn't good thing when casting on this scale.

When you think you're ready, roll the PMC into a thin cylinder a little narrower than the size of the chip you will be impressioning. Length or width? It depends on how you are going orient your impression. Each approach has its merits, but it mostly depends on how your PMC is behaving today, rather than any planning on your part (if it's too soft or sticky, try putting it in a sealed plastic bag in the refrigerator for a while. Allow it to come back to room temp *before* opening the bag and squishing it (not as much, this time) -- you want to avoid moisture condensing on the cold clay, which can can make softness/stickiness worse.


You have a LOT of leeway in the width of the cylinder. It'll squish anyway as you take the impression of the chip, and you'll be trimming away a lot of excess from he final impression before baking it. In fact, you don't need to be very precise in most of the steps (esp. with a short chip like this): the chip itself will take care of the key dimensions.

There are two basic ways to take the impression: axially or transversely. The choice mostly depends on how your clay is behaving, whether you like a really deep impression or really wide pin slots, your wire wrapping technique (in a later step), and what adhesive you use. You'll work out a suitable compromise with a little practice.

In the meantime, just cut each impression off off the cylinder with a razor, decide if it's a keeper, and make a new impression near the fresh end. When you've gone through the entire cylinder, trim your keepers to a nice rectangle, ball your rejects and trimmed bits together and roll them into a new cylinder and make some more until you've got 10 keepers.

If you find the new cylinder starts cracking or flaking in layers, condition (squish) it more

a2.jpg a3.jpg

The first picture (yellow Craftsmart™ PMC) illustrates a couple of things.

The impression on the left is too shallow for a beginner. The impression on the right is actually better, even though there is bulging and cracking (which you'll trim away later anyway). It has nice deep grooves that will be easy to follow when you wrap the wires. (but you will be able to use eitehr depth, with a little practice

But the real reason I included this picture is because the first impression (on the left) bowed back inward (due to the springiness of the clay) when I tool the second impression. Noticing this can help you "fix" slightly skewed impressions, especially in very soft PMC. While this is useful info once you get some practice, I don't advise trying to "fix" a bad impression (not now, anyway). Besides, flaws are easier to fix with a razor after baking

When you trim you keepers to rectangles (which may look satisfyingly factory sharp), you should leave a thin margin beyond the first and last pin of each row (i.e you want a 'wall' on both sides of each pin groove). You can either leave a thin margin beyond the ends of the pin grooves or trim them flush so the grooves are "open". I suggest making five each way, so you can learn which you prefer, based on your other tools and materials, later.

While I encourage you to strive for perfection during your first batch, just so you get used to the material and its properties, it doesn't matter if the grooves are slightly slanted, if some are narrower than others, etc. As I said, the chip itself will makes sure they're "good enough" to fit, and you can get away with a lot.

The second (green Sculpey III PMC) illustrates two other tricks.

The first is: if you cast you impression transversely (pins going across the cylinder), you can create longer grooves by pressing the chip in a little at a time, and gently pulling the cylinder, or pressing and spreading the clay just beyond the end of the grooves. Again, don't worry about a little cracking.

The second trick is: running a loop of Metric 1 UEW wire under each row of pins can make it a lot easier to pull the cip out of the impression. In fact, removing the chip without ruining the impression may be the hardest part of the entire process of making an adapter (but it's really quite manageable after a little practice

I use Metric 1 UEW wire for a lot of micro-electronics and even "nanotech". You probably won't find it in your local electronics shop, but you can get it at Dealextreme or PM me and I'll mail you a roll or two. "Metric 1" means it is 100 microns in diameter and UEW means "(poly)Urethane Enameled Wire" UEW insulation is thin and burns off when soldered, so you don't need to strip the insulation -- a generally nifty property, that I'll make good use of in these adapters. It's also great for making millimeter motors, tunneling electron microscopes and other nifty tools of the 21st century tinker. It's really worth having

If you can't find metric wire, Metric 1 is between 38 AWG (101.6 microns) and 39 AWG (88.9 microns) so anything in that range should work. I'll later show you how to use 30 gauge insulated wire (often sold as "wire wrap wire"), that is sold at Radio Shack and is also a very good thing to have in your workbench. Though it is technically possible to use the common 28 AWG wire (320 microns) or even 24 AWG ((510.5 microns), the commonest sizes used in hobby electronics, that's a bit advanced for a beginner: the center-to-center pin spacing on this chip is .635mm (635 microns) so you have to be more careful when using such "fat" wires

Not that 24-28 gauge (AWG) are really "fat". Those are the sizes of the individual solid wires inside CAT5/6 or telephone cable, which are often the cheapest way to buy hobbyist wire, since you get 400ft(telephone) or 800ft(CAT5/6) of wire in every 100 ft of cable

#4 Mark

  • Islander
  • 5,044 posts

Posted 15 August 2010 - 09:48 PM

Mark: Well, I did find an excellent video explanation of how to solder electronics while trying to figure out what your were doing.
How To Solder Electronics
Discussion is an exchange of knowledge: argument is an exchange of ignorance.
Peace is not the absence of conflict, but the ability to cope with it.

#5 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 15 August 2010 - 10:40 PM

Yeah, sorry about that. I'm going to edit and reorganize the material better after I'm done.

In the meantime:

Step 2: Baking the clay
By and large, you should follow the recommended temperature on the package of clay you are using -- but since we are going to be soldering on this model, we want to make sure it is really thoroughly hardened, so while you will read all over the web that 15 minutes is enough for a 1/4" object, and our impression is 1/4" tops, I wouldn't trust anything less than 30 minutes per 1/4" (6mm) of thickness and usually go an hour if I have the time

The recommended baking temperature for most polymer modeling clays is 270F (132C). A few are rated lower -- most notably the new formulations of FIMO (warning: "Original" FIMO is not the original firm, high-temp formulation of a year or two ago, but is a low-temp clay like all the other FIMO products) Though Staedtler (the manufacturer once released a statement that FIMO will not be harmed at the old 270F baking temperatures, my experience has been that ALL polymer modeling clays that suggest baking at less than 270F will not stand up well to soldering. FIMO, in particular, also fails because it is too soft and sticky.

I've read of a few that are rated higher, but I haven't tried them. They sound good, though.

Note that we are not *firing* these clays, as in a kiln. Baking performs two separate roles:
1) evaporating solvents and plasticizers; and
2) melting and melding the PVC powder -- an essential step before we proceed

PVC (polyvinyl chloride), like most polymers is a chain, branching tree or network of subunits, and its properties can vary according to the conditions of its manufacture. That's great if you are an industrial engineer, because it gives you a wide array of potential properties. For a tinkerer, it can be good or bad: bad because you have to test each candidate separately to determine its properties, and good if you find one that is perfect.

...Well, until they quietly change their formulation, but that's another story.

In our case, PVC powders that are designed to meld at, say, 230F, like FIMO are likely to begin to scorch at 351F (183C) melting point of standard 63/37 tin-lead solder, which is the kind I recommend because it has a sharp melting point. It should be able to tolerate the 275F melting point of Tix™ solder, but that stuff's a little expensive. Any PMC can tolerate the 158F (70C) melting point of Wood's metal (lower than the boiling point of water!), but that can be hard to find (PM me and I'll send you a sample to play with)

If heated slightly too high (say 300F), the plastic won't really be harmed, but it may discolor slightly. We don't care about that. However at 310-310F it may begin to stink, and the general consensus is that the fumes can't be good for you OR your project

In truth, you don't need a fully baked impression. The benefit of the method we're describing is that it uses the strengths of various materials to allow us to easily achieve an accuracy in the 10s of microns with our bare hands and naked eye. In our case, the wire we will apply later will be more important than the clay. However, anything less than a fully baked sample will make it harder to achieve success in your first few tries, and that's when you're likely to give up. Once you've gotten a few to work, it's actually easier and faster than making a Printed Circuit Board is, even for an experienced home PCB maker.

The process itself couldn't be much simpler:
1) put a small piece of paper towel on an oven-safe glass, ceramic or metal plate
2) space out your impressions (I always bake several, if not dozens, at a time) on the sheet
3) completely cover with a small tent of aluminum foil, leaving ample air circulation
4) place in an oven or toaster oven preheated to 270F-300F according to a thermometer

a) oven thermostats are notoriously inaccurate, so use a digital kitchen thermometer
b) ovens cycle up 20-30F higher & lower than the setpoint. Only the time ABOVE ~270F counts
c) make sure that no part of the paper towel of clay is directly exposed to the glow of the heating elements. The direct infrared can scorch or even ignite them

#6 gsmonks


    Tree Psychiatrist

  • Islander
  • 3,179 posts

Posted 15 August 2010 - 11:17 PM

Have you thought about doing a YouTube video of this? I think you should.
Capitalism is a pyramid scheme run by the 1%.

#7 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 16 August 2010 - 12:18 AM

That's a possibility, but I really hate setting up camera shots and the like. I do instructional video for our school/hospital, and even with a tech managing that, it's a pain.

This is currently a hack job in borrowed minutes (you can always tell when I don't have time to edit), but I'm getting a much better sense of how it should ultimately come together

I think a guidance slideshow -- or at least an image or two per step should be in the first post. Also, as I test more materials, it's becoming obvious that I should just recommend a few (though the testing itself is looking to be useful for future projects, and I'm taking copious notes, as well as producing large amounts of pre-baked samples that I will test against future needs!)

#8 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 30 January 2012 - 08:50 PM

Oops! I forgot that I never finished this one. Oh well, the idea is so simple that I'll just zip through the rest of the process.

I think I'd rather answer questions afterwards, anyway, vs. trying to anticipate them all up front.

Okay, so where were we?

Ah yes: we had a baked PMC imprint of the SMD chip which is fairly firm but still has a little "give".

Then I take an unseparated pair of cheap chopsticks (a pencil or wood dowel would work, but I use the slit to hold the first end of the wire still. You could just cut a slit in a single piece of wood with an Xacto knife or razor blade.


Now you need some fine wire. Strands from lamp cord would do, but I VERY MUCH prefer polyurethane-coated 0.1mm wire. Though the price on DX has tripled since I originally did this writeup, two years ago, it's still a bargain today: 50 rolls = a lifetime supply for you and several friends for $10 The polyurethane doesn't have to be stripped before soldering, because it melts/evaporates at solder temperatures -- very convenient!


This next step is a little tricky until you get the hang of it, but the idea is simple. Tie the imprinted PMC to the chopstick, and then spiral wrap the wire through all the pairs of opposite notches as shown below. For the size device we are using in this example, I decided to wind it twice through each pair of notches. the tops of the two wires will give a flatter surface for later soldering than the round top of a single wire.

When you're done, tidy up your work with the tip of a needle or Xacto knife. We're going to ultimately cut each turn in two places (above and below the chopsticks) so you don't have to be *too* paranoid about accidentally crossing over between turns, as long as you end up with parallel wraps above the PMC. It's optional, but, I like to insert toothpicks under the PMC to make the wires sit snug, and even bite into the PMC a little.


Now glue the wires to the SIDES of the PMC (leave the tops clean -- you'll see why later) Ordinary school glue will work. I like to use cyanoacrylate ("Superglue ™" or similar), but some people find that a pain to work with.

Now using fine scissors or a razor blade, CAREFULLY cut the  wires at the midline of the top of the PMC (halfway between the two notches in each pair. Then snip the free ends shorter, and fold them down. (This time, you really do want to make sure that there isn't any crossover between adjacent pairs.) I like to apply a little glue or nail polish to the free ends inside the rectangular central depression to fasten them permanently and insulate them


It may not be necessary, but I like to coat the wires on the sides/middle in clear nail polish (still leaving the tops clean -- you'kk be soldering to those notch-top surfaces) to make the whole arrangement sturdier

Now cut the wires in the midline of the back of the chopsticks to free the adapter, leaving a pair of free wires glued in place over each notch. The chip will sit nicely on the tops of those wires for soldering. The free end of each pair will be your electrical connection to the rest of the circuit. I usu put the PMC adapter on top of a DIP socket, and solder the wires to the legs, so I can insert the unit into a breadboard or drilled PCB, but you could solder them directly to a PCB or to a thicker standard 24 AWG wire for any other kind of circuit construction you like.

You could solder the chip in place before freeing the adapter from the chopstick, if you prefer.

Some other approaches for similar module packages can be found here

#9 Orpheus


    Get my agent! I'm supposed to be Castathan, not Indogene

  • Administrator
  • 16,868 posts

Posted 10 February 2012 - 06:04 PM

One of the bugaboos of many SMD chips is the bottom center pad. On some chips, this pad (if any) can be ignored. On other chips it is an essential ground, required for proper operation. On still others, this connection to the PCB acts as an optional or required heatsink. ALWAYS check the datasheet to know what each chip needs and why.

Any way you slice it, Bottom Center pads can be a pain, even with a hot-air station. They really expect that the PCB will be soldered in a reflow oven (or by the reflow skillet method)

However, with PMC adapters, the center bottom pad is no problem at all. When I first encountered them, in the 80s, they were mostly mandatory surge heatsinks on rather large chips, so I simply soldered a copper nail to them before assembling the adapter or PCB, and made a corresponding hole in the PMC (and if necessary, under the chip in my PCB design) This was often a better heat sink than doing it the right way in a factory.

Today's SMD chips are often far too small for hardware store copper nails, but you can often make a suitably-sized "nail" by clamping ordinary copper wire (of a suitable size) in a vice, and then hammering the end into a flat "head". In some cases, you can simply squashing the end of a wire into a tab, rather than a nailhead, and have it exit the adapter horizontally, rather than drilling through the PMC. Excess naked wire is a decent heatsink

Increasingly, very cool chips and sensors are coming in "leadless" packages which solder to the PCB via pads on the bottom of the package, and are very hard for hobbyists to solder to a PCB with a fine-tipped soldering iron.

These packages are sold under various names, depending on manufacturer, thickness, pad size and spacing, I'll just call then DFN (Dual Flat No-lead, meaning: pads along two opposite edges) and QFN (Quad Flat No-lead, meaning pads on all four edges, though not always a full complement or with the same spacing) because many distinct SMT packages are conceptually similar enough for our hand-soldering purposes

Though I've seen DFN/QFN SMD or through-hole sockets, they're rare even in surplus shops, often misleadingly similar (but not quite similar enough for a reliable electrical contact), quite expensive (often more than the chip), and some look harder to solder in place than our method (outlined below)

Hide: List of similar packages to help search engine visitors seeking other adapters

The pad spacings listed below are merely representative, based on my meager experience. Your chip may differ. The take home lesson is simply that they are often a suitable size for two turns of the 0.1 mm polyurethane-coated wire I recommended above or even a single turn of common 28+ AWG unstranded wire (26 AWG, salvaged from some cheap telephone cabling might work, if you use paper spacers, but that's really pushing it. 24 AWG is out of the question)

Some DFN/QFN pads bend around the edge of the chip. These can be soldered directly to a PCB with an iron and solder paste using hand-SMD techniques. Some have bottom and side pads, with the bend hidden by a rim of plastic or ceramic packaging, but I've been warned that you should always check that the side pad is electrically connected to the bottom pad. Not all are. I don't know why. Maybe those side pads are grounds or for special chip carriers.

a2.jpg a1.gif

This is so similar to the PMC adapter above, that I don't think we need more pictures. We're basically winding the wire around the chip itself, instead of a baked Polymer Modeling Clay impression. Double-faced tape will help a lot, though there are alternatives. I also suggest stacking MULTIPLE chopsticks, thick rectangular artist pencils some other slightly larger winding base: the extra thickness will give you extra lead length on every turn of wire, which you'll definitely need to reach the corresponding DIP pins, for anything much larger than a 6-pad DFN. It's a lot easier to trim excess wire later than to struggle to wrap a stubby lead wire (pair) around a distant DIP socket leg.

1) Wrap your double-faced tape completely around a length of your thick winding rod. (if you end up doing a lot of these, you may decide to notch the backside at 0.5mm intervals with an Xacto knife, and only use a tiny bit of double-face tape to hold the DFN/QFN

2) attach the DFN/QFN upside down (pad side up) to the double faced tape (or glue it with water soluble glue)

3) wrap the wire around the DFN+rod, as we did above with the PMC+rod, two turns of 0.1mm polyethylene coated wire per pair of opposing pads. The double-faced tape will help you maintain 0.5mm spacing between each set of paired wires

4) with a toothpick or fine pin, apply cyanoacrylate ("superglue") to glue the wound wires to the PACKAGE, trying to leave the pads completely clean

5) I prefer to solder the wires to the pad using a toothpick cut at an sharp angle (the way quill pens are sharpened) to dispense the solder. Rather than apply the paste to the wire and then heat, I heat the wire with my iron and then touch the solderpaste-laden toothpick to the wire to form a good, well-filleted joint

6) once all the pads are soldered, use fine scissors or an exacto knife to cut the wire connecting the pairs of opposing pads on the bottom of the DFN.

7) flip the winding rod and cut the wires on the back to free the DFN from the rod. I like to "tin" 8-10 mm of each wire pair (i.e. lightly solder the pair together) in the middle of the back of the rod, and then cut in the middle of the tinned area. This makes the free ends MUCH easier to handle

7a) For QFNs, turn the QFN 90 degrees, retape it to the winding rod, and repeat the above steps for the other pad rows

8) as before, mount the DFN/QFN in the middle of your target DIP socket, and solder each lead wire pair to the corresponding DIP pin leg. I personally find it easier to solder them pad-side up, but this reverses the pin layout. If that matters to you, consider mounting the DFN/QFN pad-side-up to the bottom of the DIP socket or pad-side-down on top of the socket. It's pretty much equally easy either way. JUST MAKE SURE YOU KNOW YOUR CORRECT FINAL PIN LAYOUT. It's pretty easy to confuse yourself, since the DFN can be mounted pointing north or south, pad side up or pads side down (relative to the DIP PIN numbering) and the DIP socket may be soldered to the top or bottom of the PCB

This is such a simple idea that I almost feel embarrassed to mention it -- but I've seen a LOT of delays when someone *didn't* think of it. To most hobbyists and for initial design, through-hole components like DIPs are easier to work with (e.g. in proto-boards/breadboards), but when you get to the PCB prototyping stage, drilling all othose holes is a pain, especially if you're etching your own boards.

Fold the legs of a DIP chip under its body, snip off any excess, et voila! instant (oversized) SMD chip!

When doing your PCB layout,  select a through-hole component (for proper spacing). Just because there's a hole in the pad on the PCB doesn't mean you have to drill it out. Just solder the folded legs on top of the pad, SMD style.

1 user(s) are browsing this forum

0 members, 1 guests, 0 anonymous users