It is important to pick the right place to manufacture the prototypes. Here are some of the places, I used to manufacture circuit booard. I am always trying to be on lookout for new places.
As a rule of thumb right now, I use PCB Cart for multilayer small designs, OSH Park for large boards, and Kind Credie (FPC) for flexible boards. For the assembly places, I don’t have strong preferences but will list some companies I used before. Assembly can be much more expensive (5X or more) in the USA, versus China. Some companies (e.g. Advanced Circuits ) can do both manufacturing and assembly.
Manufacturing the boards
PCB Pool
This is a very good place for getting standard 4-layer boards. They also provide free stencils, which are very useful in assembly. I don’t use PCB pool as often since they don’t provide many options. For example, the thinnest board is 1mm.
If you have a 4-layer green solder mask board with 1 mm thickness, this is the place to order.
PCB Cart
This has been my go-to place recently for small and complex boards. They have many customization options (color, thickness) and can provide a $10 stencil. Generally, the quality of the boards I got from them has been very good.
OSH Park
If I have a big board that I want to make, I use OSH Park. It is quite affordable and has a great automated ordering system. On the downside, the design options are quite limited to thick boards with one solder mask color.
King Credie
This is a where I get all the flexible and rigid-flex boards. They always do a good job and relatively inexpensive for flex boards designs (around $200 for simple design). On the downside, they don’t have an automated online ordering system. You would have to talk to them over email to order, so it can add some time.
Advanced Circuits
This is a popular factory, located in the US. I found that the boards from Advanced Circuits are similar to ones from PCB pool, but more expensive. I don’t really use this place anymore, but it is quite reliable. They also provide assembly services in the US, so manufacturing and assembly can be conveniently done in one place.
Dirty PCBs
This is a pretty good place for getting inexpensive boards. They also provide stencils. The boards can be a bit sloppy. For example, they usually add an identification number on the back of the board.
Unlimited Stencils
If the board manufacturer does not provide stencils, this is a good place to get them. They can provide both Kapton or steel stencils.
Assembling the boards
AQS
This is a contract manufacturer company. They have facilities in China and California. They can provide a lot of services including circuit assembly.
PCBA
This is a circuit assembly place in Seattle. They are especially good if you are local, as they can come and pick up parts directly.