This is a technological discussion on designing a fabrication friendly PCB

Step 1: I will list the types of PCB design start with the most important as the following.

1.      Blind/buried via

Blind via hardly be drilled with mechanic drill. Usually, laser drill is required to make them. It adds extra costs to the drilling. As for buried via, unlike through-via which is made after the lay-up stage, they will force the fabricator to divide the lay-up process into several stages. Each of the buried via is drilled as a blind via before another layer being laid up on it. For example, there is a buried via from layer 2 to layer 4 in a 6-layer-board. They fabricator will lay-up the board 1 and 2 before drill this via. Then lay the board 3 on top of it.

It will be more difficult when there are one or more layers which multiply buried vias drilled through but into different layers. For instance, via A through connect layer 2 to 4 and via B connect layer 3 to 6 in a 6 layer board. In fabrication, board 1 and 2 will be laid up to drill via A first. Then, board 3 will be laid on top of it for drilling the rest of via B. If an error occurs in drilling via B, the entire board must be discarded.

Blind/buried via will increase fabrication price dramatically. For instance, half of the quotation from my fabricator for 5 boards is about 15$. However, if blind/buried via is added to the design, the price will be 150$ or higher. Therefore, blind/buried via is the first to avoid in designing a fabrication friendly PCB.

2.      Dense trace and small via

Narrow trace, small via and narrow space between separated cooper areas all add extra costs to the fabrication. My fabricator can fabricate 4mil trace/space. But 4mil design is recommended due to higher defection rate. For instance, the 6mil trace design costs 16$. The same model with 4 mil trace design will cost 103$. It is the same for the via. Depending on the fabricator, usually 0.2mm trace/space and 0.3mm via diameter is the pricing boundary in a cheap PCB fabricator. The price grows dramatically if the design goes blow these values.

3.      Board material

Most of my customers do not specify the PCB material. My fabricator uses low Tg (glass transition) FR-4 as the default board material. Some of PCBs are designed to work under high temperature, thus use medium or high Tg material. The board material takes a large portion in the price especially in cheap fabrications. For instance, 5 piece of low Tg board cost only 16$ in my fabricator. If the customer choose medium Tg material, the price will be 37$, and 185$ for high Tg material. My recommendation is to make a more precise estimation of the working temperature and dielectric constant of the board in order to choose the most economical option.

4.      Surface Finish

The cheapest option is hot air solder leveling (HASL) with lead. I found that most of my domestic customers prefer the cheapest lead finish, while my international customers do not like lead and prefer gold which is the most expensive option. To be more specific, on the basis of the quotation from my fabricator, lead finish cost 16$, lead free cost 37$ and immersion gold costs 48$. I suppose that a bit lead for prototyping does not hurt that much. Some of my customers prefer plated gold on the entire board. If the customer uses the board for testing, which is what my fabricator specialized for, I would not recommend it. Plated gold is much more expensive than immersion gold and less soldering friendly. Moreover, it is not needed once the board is assembled. You might need expensive finishing once the designing hit small production. As for prototyping, my suggestion is to choose the cheapest option on the finish.

Other aspects like the number of layers, board thickness, and cooper thickness also affect the price. Most of my customers understand how to control budget on those aspects. I will skip this part.

Testing is necessary especially for cheap fabrication. Most of the fabricators conduct the tests by default. This testing cost is relatively low but may not be for free. For instance, my fabricator provides free tests for prototyping board. Even the testing cost for small volume production is little to be concerned. I have seen discussion from customers whom received defected board from some cheap fabricators. It would be wise to ask for the testing if the fabricator do not mention about it.

You should not expect the customer server of your PCB fabricator to improve your design. The fabrication price vary from different fabricator, so that you may not be aware of a tiny design flaw increased the costs. To sum up, in order to design an economical fabrication PCB, do not just stick to your original design concept. Keeping some margin to the capability of your fabricator and check all the fabrication alternatives it provide may greatly reduce your costs.