While the modularisation of the MEGAphone makes it easier to assemble and test the device, it doesn't completely do away with the need for surface mount (SMD) soldering.
So let's explore some ways that we can help to make that more approachable at home, or in austere environments.
There are five approaches that can be considered (let me know if you think of others in the comments, and I'll update the post):
1. Phone a Friend!
The first option is, quite simply, to find someone else who knows how to do it, and is willing to do it for you!
Pros: No new skills or equipment required.
Cons: They might not be available or willing for all sorts of reasons.
2. Online PCB Assembly service
The next option is to pay some online service to make batches of modules. This is particularly effective if you want to make a bunch of units for yourself or a group. You could even make a kind of syndicate where each person orders a few types of modules in larger quantity, and have them all arrive at one person's address, who then makes up kits of the sets of modules you need, and distributes them to everyone.
Pros: No new skills or equipment required.
Cons: More expensive. Requires some scales of economy to be cost-effective. Involves logistics and probably international shipping etc to be working in your location.
3. Hand-Soldering
You can of course still hand-solder, but this can be quite fiddly for some component types, and almost impossible for others, e.g., ball-grid arrays. Whether that ends up being a problem is yet to be seen, based on the component choices I am able to make, but there is a significant risk of at least one component somewhere being like that. Currently the high-current DC:DC converter falls in this category.
Pros: Cheap and simple tools.
Cons: Requires considerable skills and increased risk of things going wrong. Also some components are just not feasible to reflow this way.
4. Hot-Air Reflow
Or you can use a hot-air gun or hot-air reflow station. I find this method to be quite fiddly and difficult to accurately control the heat. Also, you can blow components away, or scorch things due to the focused application of heat at very high temperature.
Pros: Relatively cheap equipment.
Cons: Hard to get right. Easy to scorch things.
5. Reflow Oven (Commercial or DIY)
Then there are reflow ovens, such as the cheap T-962 units, that with a little adjustment, perform okay. They are quite physically large, however. Also, if you use a T-962, you probably also want to replace the controller with a sensible after market one, which cost about as much as the T962 unit itself! The combination will cost you about 600 - 800€. Or you can buy one pre-modified for about 1,200€ plus postage, which to Australia is probably another 200€ - 300€. Then also import duties etc.
Also, it looks like the T962C works fine out of the box, but is a bit larger. For me, it also has the advantage that the top stays cool, so if the cat gets into the shed etc, it won't be a big problem. I can probably also stack it under some of my other tools. The trade-off, is that it vents through the bottom, which is not great for whatever bench you have underneath, nor for efficient extraction of fumes from the workshop. These are about 600€, or more like 900€ by the time they get down here to Australia. This is still enough to trigger import duties.
Pros: Does a great job.
Cons: Relative expense and size.
6. Hotplate (Commercial, DIY or improvised)
Finally there are soldering hotplates, varying from quite small commercial units with ~5cm x 5cm plates, through to bigger ones with more like 15x15cm plates. The commercial ones don't tend to do reflow curves, but rather just heat to a constant temperature, which is a bit of an issue. Also, the larger ones especially, have high thermal mass, which means that the time it takes to cycle it cool again ready to handle the next board(s) can be longer than you'd like. Also, the exposed hot top can be a risk for people or animals touching it (our cat tends to find ways into my workshop, for example).
There is an ingenious DIY version of this, which uses copper traces on a custom PCB to provide the heating. It does support temperature curves. What the lifetime of this approach is, is unknown, as it does involve heating the PCB it is made of itself each time, which will likely fail at some point.
Pros: Fairly easy and low-cost. Some are even just USB-C powered!
Cons: Larger ones are a bit more expensive, and hold heat for a long time, without a protective cover, making a bit of a safety issue.
7. Sand in a Fry-Pan
As it sounds, this is just putting some fine sand in a frying pan and heating it on your stove. It's cheap, and if you have fume extraction above your stove, sounds reasonable, provided the people you live with don't mind. It's not perfect in terms of results, however. You can get a sense of the comparison of this with hot-air and a T962 reflow oven from Great Scott's video here:
Pros: Even cheaper alternative to hotplates. Most people have access to a pan and a heat source.
Cons: Fiddlier, and less reliable.
8. Decision
Okay, so now I need to make a decision -- or at least an initial decision.
I think initially I'm going to get one of the 5x5cm USB-C hotplates, as they are small and cheap, and feel like they would be a good option in an austere environment. Also, it's a technique that I feel that I could easily master, and that I have yet to try.
Watching this video:
I found out about a hotplate that is only US$20 and that still seems to work. The postage to Australia is more than the unit itself!
Anyway, I've ordered one, so that's that. I'll post again when it arrives, and let you know how it goes, when I have some PCBs arrive. I'll probably put a PCB order in next week or thereabouts, once I have enough of the module PCBs designed for the MEGAphone to make it worth the postage.
I'll work out what to do about low-temperature solder paste at the same time.
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