Experience with Printing Circuit Boards

Maker Talk
1

Does anyone have experience converting an Arduino-based circuit into something that can be made more efficiently?

I have a simple circuit that receives commands over bluetooth (using an HM-10 chip) reads a load cell sensor (via HX711 chip) and controls a ~8 amp line with a few mosfets. I can solder the circuit together, but it takes a while and I frequently have minor faults in the connections that take forever to identify and fix.

As a result, I’m looking for a way to get my circuit printed, ideally with the components already soldered on. Do any fellow hackers have any experience with this?

2

Best thing to do is design it and have it made. Printing is laborious

3

I’m not sure I follow, you mean I should just continue soldering it by hand?

4

It you design your circuit board. You should have it made in China. It is less expensive and more reliable.

5

Been a while ago but I have designed a circuit and circuit board using EagleCAD (which apparently is now owned by AutoDesk) and had it manufactured using a service previously operated by SparkFun.

I think SparkFun sold it off to OSHPark https://oshpark.com/#aboutus which can take your PCB design files and make boards for you pretty cheaply for hobbyists. $5/square inch for 3 copies of a design. This is cheap because it is so automated.

Having someone build up the boards with your components however will likely get costly due to the low volumes involved.

Steve

6

Yeah, I spent way longer than you can imagine becoming an expert engraving two-sided PCBs on a CNC (also etching PCBs) but I’ll say right now it’s not a good use of time at all anymore. It’s incredibly difficult to get right with fine details, and there’s no soldermask or plating on throughholes and no good way to do more than 2 layer.

Best deal around is PCBWay: https://www.pcbway.com/orderonline.aspx

Fabricating the PCBs, including >2 layers, is really cheap and about 2 weeks to get here.

Assembly is something worth doing yourself though. It’s challenging, and a useful skill. Getting parts to PCBWay and getting them (or anyone else) to do the assembly gets pricey, difficult and logistically complicated, and error-prone. They have to acquire the parts or you ship them to them.

Actually, almost all parts can be done at home. Once you get used to a hot air rework station and good technique, SMD is actually WAY faster and easier than leaded components. The fine-pitch SMD stuff is actually easy, you just flux it up and run a ball of solder down a whole side and then clean off the excess with solder braid and check for bridging, which is easy to fix. But, you do need a stereo microscope- not too expensive nowadays

7

That is very helpful, thanks guys. I think I’ll get someone on fiverr to design the PCB, then use PCBWay or 4pcb (if I’m feeling impatient) to get it printed.

I also think I’ll use through hole for everything, as I believe the 8A line will be too much for SMD.

In case I later on end up going down the SMD route, does the hackerspace electronic lab have everything needed to do that?

8

That’s not too much:

8A in standard 1oz copper with a limit of a 10C temp rise would need to be 0.208in wide trace if on one of the outer surfaces. It won’t matter if you use throughhole or SMD. The thermal properties of the component are usually more advanced in SMD components. MOSFETs in SMD packages solder straight to the copper for heatsinking.

Most MOSFET switching can be done with minimal heat generation while “on” and the only significant heat generation is during the instant of switching when it’s only partly on. This makes high speed PWM switching more challenging, but normal switching is just a matter of designing the gate drive so it switches quickly and efficiently between “on” and “off”

9

Are you soldering the chips directly or are you soldering breakout boards together. Those are very different problems.

If you are soldering breakout boards together, I’m not really sure of what advice to give you.

If you are dealing with the chips directly and the HM-10S/HM-10C as a castellated module, I think ExpressPCB will assemble boards for you for about $500 (presumably base–parts will probably need to be added).

I would use a 4-layer board (signal-GND-VDD-signal) unless you have an amazing reason not to–2-layer boards make your life miserable with routing, power distribution, and heat dissipation. The cost differential just isn’t worth it unless you are shipping 100,000 boards.

You might have a bit of an issue in that I can’t really seem to find a reliable/trustworthy supplier for the HM-10S/HM-10C castellated modules (Seeed has the HM-11s so they might work). That means you will have to buy the parts and ship them to the assembly house–that’s probably an extra charge.

In terms of designing boards, use KiCad. It’s more than adequate for what you are doing. It’s open source and sponsored by CERN who figured out they were paying so much to PCB board software houses that they could fund it themselves. It works on Windows, Linux, and OS X (maybe not the latest M1 Macs though). I use it for all my BeagleBone capes. There are lots of tutorials and videos all over the place about using it. I use more professional PCB software for work and let me tell you that KiCad is perfectly fine to do PCB work in.

I would suggest, however, that you switch to all SMT components if you’re going to use an assembly house. Through hole requires hand soldering operations (read: expensive) while SMT allows the assembly house to stencil the solder paste and then pick and place the parts in a fully automated fashion (they probably use humans for this on orders of 10 or less, but the expense of through hole still remains).

In terms of hand soldering, I oddly find that SMT SOIC packages and 1206/1210 SMT components are much easier to solder by hand than through hole packages and 1206/1210 components are large enough that I can solder them without a microscope even with my aging eyes. I will suggest that you need two soldering irons though. Soldering SMT passives like inductors/capacitors/resistors is dramatically easier if you can hit both terminals with heat simultaneously.

One thing to be cognizant of is that an assembly house will default to Pb-free solder. This requires quite a bit more heat to melt if you have to do hand rework. I find that I generally have to add leaded solder to the solder joints in order to bring down the melt temperature for hot air guns to work.

HOWEVER …

If you go all SMT, you have an extra option that you didn’t have before–you can stencil and reflow the boards yourself.

You need some solder paste. And you also need to buy an SMT stencil printer (as low as $60 on AliExpress–but I strongly recommend the $300-$500 range ones–the difference is in the number and accuracy of the vernier adjustments). And you need to buy some sort of “reflow oven”–that can be a cheap toaster oven depending upon what you need (note the one in the ATXHS electronics area) or you can get one of those from AliExpress (I think you can get those as low as $200) and there are lots of videos about how to use them for hobbyist work.

At that point, you can print the paste on the board with the stencil, place the components by hand, and run the board through your “reflow oven” to solder it. For SOIC and 1206/1210 components I find that setup works really well and I almost never get shorts. The stencil cuts back the amount amount of solder so you don’t oversolder the joints, and the surface tension of the solder gives you quite nice joints on the SOIC and prevents short circuits.

If you have a problem, generally it’s that a joint didn’t fully solder rather than shorted out. And that’s easy to spot under a microscope or magnifying glass as you’ll see little solder balls still intact. You need to hit that joint with your soldering iron or hot air gun and finish it off.

Hope this helps.

-a

10

I find it vastly easier to use 0805 to 0402 components and hot air them on with regular solder. I don’t use stencil and paste.

Use a soldering iron to wet both pads. Then apply hot air and put the part in with tweezers. It will self-center. I work entirely under a microscope. It’s surprisingly fast and easy.

I’ve also used the soldering iron to solder down one side of the component, then the other. The first side will freeze in place before you can get to the other, so it’s not always well-centered. You can always follow up with hot air and it’s simple in that you don’t need to drop the part in with tweezers at this stage. Often though this isn’t simpler.

You need to get a feel for how much air to use, too much and it blasts off prior placed components nearby and melts plastic stuff. You do need to think about the order you’re doing things in. If there’s a problem with blasting off other components or melting plastic stuff, you can apply temporary Kapton tape to protect these features.