Ordering Circuit Boards

PCB Options

There are a number of different options available when ordering PCBs. Not all services provide all options, so knowing what capabilities you want can be an important part of picking an appropriate service. Here are some of the main options to consider. (Note that this discussion assumes that you’re going to be soldering the components to the PCB yourself. If you’re planning to have boards automatically assembled by machine, you’ll need to coordinate these options with the assembly service to ensure that the PCBs are compatible with their processes.)

Number of Layers

This is probably the biggest differentiator between services. Two-layer boards are the cheapest, with four layers often a good bit more expensive. Many services don’t support more than four layers, and those that do are expensive. Typically, you won’t save any money or time by ordering a one-layer board vs. a two layer one.

Of course, the number of layers in the board isn’t something you can change if you’re just trying order a copy of an existing design, so there’s not much to choose here. Just look for a service with the right number of layers.

Solder-Mask and Silk-Screen Layers

Whether or not to get solder-mask and silk-screen is probably the biggest choice you have to make when ordering a board. Foregoing them can save money and time, but unless you’re confident in your ability to solder the board without them, I’d recommend getting the solder-mask and silk-screen. To tell whether these are included or not, look for phrases like “No mask. No legend.” or “Green mask. White legend.” Services without solder mask and silk-screen layers are often called “basic” or “bare-bones” or similar. Some services charge extra to get silk-screen on both sides; again, I’d omit this only if you’re confident you won’t need to refer to the labels on the bottom of the board.

Board Shape (Routing)

Some services will only cut boards out as rectangles, or in other simple shapes. You can order boards that were designed with more complex shapes, you’ll just get them back as rectangles. (The copper itself will still have the correct shape.) Other services charge more for complex shapes (which can include something as simple as a rectangle with rounded corners). Cutting out the board is typically referred to as “routing” as in “Boards are routed as rectangles or circles”.

Note that internal cut-outs (besides simple circular holes, which are drilled) are not necessarily a standard element of most PCBs. You’ll often need to pay extra to get these routed. In addition, you may want to provide a special comment noting the existence of the internal cutout, so the board service doesn’t miss it.

Finally, note that services have maximum and, often, minimum board sizes. You’ll need to check these against your design.

Color

Some services let you pick a different color for your solder mask, instead of the usual green. You may have to pay extra for this. OSH Park makes all their boards purple.

Turn-Around Time

Different services offer different turn-around times. Typically, the faster you want to get your boards, the more it will cost. Faster services will make your board the day or the day after you order them and ship them to you overnight. Slower services might take a couple of weeks. If you order boards from China and want to save on shipping, it might take a month for them to arrive by sea. In the services section below, I’ll describe the turn-around times offered by the various providers.

Quantity

The more boards you order, the cheaper it will be. Even low-volume prototyping services tend to have a minimum quantity of two to four boards. If you just want one board, look for the cheapest total price but be aware that you’ll probably end up with some extra boards (which can be useful if there’s a problem with the first one). Again, I’ll discuss the quantities offered by the various services below.

Specifications

PCB services typically provide detailed specifications about various aspects of their boards. Often, you don’t need to worry about these (the defaults are usually fine), but I’ll describe some of them here so you know what they mean. The standard thickness for a PCB is 0.062″ or 0.063″ (about 1/16th of an inch, or 1.6mm). The default copper thickness for two-layer boards is usually 1 oz. (the thickness resulting from distributing an ounce of copper over a square foot of material, or approximately 0.0014 inches). This is probably fine. Four-layer boards may have thinner copper layers (e.g. 0.5 oz.). You may also have multiple options for the finish of the copper; again, the default is probably fine. You may also be given details about the composition of the solder-mask, but I’ve never needed to worry about what they meant.

The other important specifications refer to the minimum (and maximum) sizes for various features of the circuit itself. For example, vendors will typically specify a minimum thickness for the PCB traces (copper connections) and for the distance between adjacent traces. These are usually specified in mils, or thousandths of an inch. For example, “6 Mil line/gap minimum” means that the traces need to be at least 0.006 inches wide, and at least 0.006″ apart. You’ll also see minimum drill sizes; these refer to the smallest holes you can get in the board. Unless you’re ordering a very sophisticated board, however, you probably won’t run into these minimum sizes. (For example, I personally never use traces thinner than 0.008 inches, which is above the minimums for most services.)

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