Ugly SMD Adapters

Adapter PCBs for ugly or Manhattan breadboarding with SMD parts

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"Ugly" construction has long been a popular breadboarding technique for analog and smaller digital circuits, especially when using an iterative design approach. Back in the days of through-hole parts, it was easy: grab a piece of copper clad for a ground plane and solder together a mess of connections in the air above it. With today's SMD components, it's not quite that easy. I've tried finding suitable commercial adapter PCBs, but most of them are aimed at adapting to 0.1" through-hole headers, and the plated-through holes can short to the ground plane when you mount them ugly-style. So, a few years ago, I ended up etching a large batch of my own single-sided adapters specifically for this construction style. I'm now coming to the end of that batch, and decided to make and share open-source (MIT license) Eagle designs for a new set of adapter boards.

I know you could argue that this construction method is closer to the "Manhattan" style, but these adapter boards sure aren't pretty! In any case, I've found that it works pretty well.

The artwork I used for my original batch of home-etched adapters is probably lost forever. Luckily, it only takes a few minutes to put together a workable adapter board design in Eagle. I've released the following 10 initial designs so far in the GitHub repo:

  • 4x_0603 - I usually use through-hole passives, but just in case, this board holds (4) 0603's
  • 4x_0805 - same thing for the 0805 package
  • 4x_1206 - again for the 1206
  • SC70-5 - a common tiny package for analog and single-gate digital ICs
  • SOT23-3 - diodes and transistors
  • SOT23-5 - analog ICs and single gates
  • SOT23-6 - analog ICs
  • SOIC8 - always needed for something
  • TDFN33-10 - I needed this one for a TS3004 oscillator/timer from SiliconLabs
  • TSST8 - this one is for a dual N-,P- channel mosfet

One problem with the home-etched versions was the lack of soldermask, which allowed bridges to easily form between pads. Of course, the new designs include soldermask and silkscreen layers. Here's a rendering of the SOT23-5 board:

The silkscreen mirrors the traces underneath so you can tell which pads are which - it's more important for some of the other packages. I've used either 0.1" square solder pads as in this example, or 0.05x0.1" for some of the higher pin-count parts. I found either size easy to prototype with; an added mask should make it even easier. The package name is on the bottom silkscreen so you can easily find the correct board in a big bag of them.

NOTICE: as of 7/22/16, I haven't tested *any* of these designs yet - they just went to the fab last night. Some or all of them may be defective in some way. When I've tested them all out, I'll update this note (and the repository, if necessary). Once I know they're good, I'll also share them on OSH Park.

In keeping with the "ugly" theme, these designs aren't particularly elegant or polished. There may be some refinement after the initial boards come back, but if they work, I'll probably just leave them. As I have need to prototype with devices in other SMD packages, I'll add them to the repository.

As shown in the header image, I sometimes use one of these adapters with DIP ICs that need to be socketed - otherwise, I'm a fan of mounting them "dead-bug" style. I plan to make similar designs for smaller DIP packages (8, 14, 16) and corresponding SOIC/TSSOP packages, but that's all that I have planned for now. If anyone would like to contribute a design for a package not included here, or has suggestions for other useful packages, please let me know.

  • Castellated Edges

    Ted Yapo5 days ago 0 comments

    I haven't been good about updating this project, but I've been using these adapters very successfully. Most recently, I've started adding castellated edges for soldering to the ground plane. Here's a look at some under the 10x inspection microscope:

    This board was (obviously) made at OSH Park, using their castellation guidelines. As you can see, the outer cut can leave a little bit of extra copper foil attached to the hole. This is easily removed with a knife, a file, or sandpaper. If you were using these for connecting individual signals to a base board, you would probably want to remove them before soldering to avoid possible bridges. Since I'm using them for ground connections, I didn't bother, and just soldered them to the ground plane as is. The result isn't particularly attractive, but it works:

    These particular adapters were made for SOIC logic packages for the #PIC Graphics Demo. The project uses 74AC logic, which has a reputation for causing trouble with ground bounce and with signal reflections due to very fast edge rates. As a result, systems built with 74AC can be more sensitive to layout than other logic families. I wasn't sure how well the castellated ground connections would work, so I also removed the soldermask from the bottom ground plane on the adapters:

    The idea is that you could reflow these adapters to the solid copper clad ground plane if you wanted. As it turned out, just connecting the grounds with the castellations worked for this particular project - although the bare gold is right next to the bare copper, closely coupled capacitively, if not conductively. I don't know if it would work for everything. For 74HC gates, there should be no issues just connecting the castellations.

    As you can see in the image, there are sites for bypass capacitors on the boards; they assume the standard corner power-pin layout of logic ICs. In that sense, they're not totally general-purpose, but they could be used for any logic gates in standard packages.

    The solder pads are 50 mils square, and spaced 100 mils apart. This is a comfortable pitch for me to hand-wire boards with wire-wrap wire - the 50 mil pitch of the SOIC parts is just a little too small.

    One thing I want to try is making adapters for wire-wrapping SOIC gate packages. Some ICs are no longer available in DIP packages, and wire wrap sockets are very expensive. Adapters that mounted SOIC parts and 25-mil square gold header pins would solve both problems. Also, the low-profile of the SOIC parts would let you mount the pins on the top side of the board, with room to wire-wrap over the ICs - where did I see this around here? No more reversing the pin layout in your head!

    Finally, here's a completely unrelated board that shows how easily the original adapters mix with more traditional prototyping.

  • First batch (twice!)

    Ted Yapo08/23/2016 at 17:26 1 comment

    The first batch of test boards arrived. Actually two batches did: USPS "misplaced" my first shipment for ten days, but found them again just after OSH Park rush-ordered a replacement set. Here they are:

    I have a few projects that have been on hold until these arrived, so I'm excited to test them out. I'll post progress as I do.

    These first boards must be glued to the copper-clad backplane. As a next step, I'm going to try some boards with three different ways of soldering to the plane:

    • bare pad bottoms skillet-reflowed onto the plane with solder paste
    • an outside ring of through-holes to solder to the plane
    • castellations around the board perimeter

    It turns out that OSH Park supports castellations, so that sounds like the most promising approach, but I'd still like to test all three.

    Next Up

    As to which packages to support next, I'm running out of small DIP adapters. Here's a few I used this past weekend:

    (Left) A 10-bit DAC is plugged in while I wait for a 12-bit unit to arrive; the adapter board makes mounting a socket on the plane easy. (Right) Half of a DIP8 adapter board makes a convenient mount for a 4-pin header for connections to a daughterboard.

    Stay-Clean Boards

    I used another trick on the above prototype to preserve the copper ground plane. I cleaned the copper clad with "Barkeeper's Friend," a scouring powder containing a fine abrasive, then rinsed it thoroughly. Once it dried, I spray painted it with a light coat of clear enamel. This coating protects the copper from corrosion, but is easy to solder through when connecting to the plane: it will keep the boards looking pretty for years to come. I read about this technique a few years ago on Charles Wenzel's site, but haven't been that good about actually doing it. I finally got motivated, and coated a few large pieces of copper-clad, so I can just cut them up with a shear as I need pre-coated pieces.

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Patrick Allison wrote 08/02/2016 at 12:36 point

OSH Park does castellations. They're not perfect, but they're usable. I'd really recommend using those. Doing a two-part assembly like you're suggesting is actually really a pain to get working: the small boards reflow first, since they've got less heat capacity, and it's tough to tell when the backplane reflows if the only contact point is below the board.

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[this comment has been deleted]

oshpark wrote 01/04/2017 at 18:57 point

Here's our tips for Castellated Edges:

Please email if you ever have an questions or want us to check a layout before ordering it.

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Stuart Longland wrote 07/23/2016 at 12:02 point

How hard would it be to have the boards bordered by plated-through vias that then connect to the ground plane?  You'd then be able to solder the little board into place instead of having to glue it.

Some packages actually have a ground pad directly underneath the chip which could then be connected via this, reducing the effective series resistance quite considerably.  (There's about 1.5nH per mm in a PCB trace.

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Ted Yapo wrote 07/23/2016 at 15:19 point

That's an interesting idea.  I had thought about trying to add castellations around the board perimeter to solder to the plane, but hobbyist PCB services don't seem to support them.  I'm wondering how difficult it would be to get enough heat in there to solder the through-holes to the ground plane?  When I've tried to solder small double-sided pieces of copper-clad back-to-back on the ground plane, I've always had trouble.

It would be nice to get away from super-glue - it takes too long to set and often fails at just the wrong time unless I thoroughly scour the copper to remove oxides and whatever. Then again, when I need to rip-up a board to modify a design, it usually just pops off with a screwdriver.

With these adapters, I typically use a stout bare copper wire (or sometimes a short section of desoldering braid) to connect to the ground plane.  That's not too bad - but it doesn't account for the trace, as you point out.  I was wary of beefing up the traces too much because it might reduce solderability for the IC pads.

Yes, for packages with exposed pads, a bunch of vias underneath could really help - also for power dissipation.  I guess even if you weren't able to easily solder the holes down, you could use a bit of thermal grease under the adapter to promote heat transfer.

The boards are cheap enough - I'll make a quick test design with some vias I can try soldering down.  The funny thing is that using the OSH Park fab, I had to add one "fake" via outside the board outline anyway - this forces the creation of a drills file (and bottom copper layer), which is necessary to use the service.

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jaromir.sukuba wrote 07/27/2016 at 13:27 point

Soldering the boards to ground plane shouldn't be too difficult provided you have reflow soldering oven. Or hot air gun. Or at least classical clothes iron on highest temperature - once upon a time I used it to solder QFN packages. Though I've never tried soldering small PCBs on top of other PCB.

The other problem with super glue - it smells AWFUL when heated by soldering iron.

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Ted Yapo wrote 07/27/2016 at 13:57 point

I hadn't thought about reflow for mounting the adapter boards.  That's a very good idea!  I use an electric skillet for reflowing boards, and figured I'd do that for mounting the finer-pitch parts on the adapters.

I might even get a two-for-one.  Place the adapters on the ground plane with some solder paste, then place the components on the adapters, and reflow the whole assembly.

I'm guessing the super-glue fumes aren't very good for you, either.

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