- Sun Sep 14, 2014 5:17 am
#535
No big deal, yes China is different from Western countries regarding PCB manufacturing.
IPC rules of course still apply, but labor is so cheap there, that some premiums that you will pay here do not apply there. Also, given the volumes they produce, they have higher-speed / better quality equipment than small old European shops (this is less and less true, as more shops are now moved to former Iron Curtain countries...), and they tend to standardize the needs into several typical PCB grades.
Basically, you have only a few different grades: the worst is using single sided Bakelite with wire straps and is used in white goods and or low-quality consumer goods like power boards for TV sets, DVD that are sold by millions, so saving $0.10 is important here.
Then you won't save much by having other single-sided intermediate grade below 6 mils trace width / 6 mils spacing / 0.3 mm holes, know as "prototype" grade, with thickness down to 1.0 or 1.2 mm instead of standard 1.6 mm in order to save on epoxy, and using as little as possible glue to clad the copper, so if you heat too much, traces will lift up easily
Then you have the "RF" grade, which has the same constraints, but with impedance matching, thus higher grade epoxy material with controlled permeability and temperature grade.
Highest grade is "BGA" with laser buried vias and gold finish, usually with 4 mils trace width / 4 mils spacing / <0.2 mm holes.
Of course, there are variations around these grades, but usually if you stick to them, you won't have any surprise.
As for thermal relief, it is only useful to avoid having to provide a lot of heat in order to bring a large copper plane to a temperature high enough so that solder will melt. But for boards smaller than a few cm2, it is better to use solid plane that will in fact spread the heat more evenly and avoid having colder areas where you will have SMT mounting problems.
Having components close to the board edge is absolutely no problem because of panelization, even in Europe, unless you do large boards where edges will prevent pick&place machines to go near the edges.
Back to the reference design, I think a 4-layer board here is luxurious
As you can see if you look at all the Chinese-made small boards with an ESP8266, they are all 2-layer only, 1 mm thick "RF" grade at most, if not "prototype" as nobody will notice the difference
If we need to do some layouts, starting from these boards will lower the cost of the board dramatically: see the price you can get at "Dirt Cheap Dirty Boards":
http://dirtypcbs.com/You get: 10 copies of each board, 2 layers, 1.0 mm thick any color, 100% tested, 50 x 50 mm for $14, free shipping...
