Since we launched the PCB customization features, you’ve asked us for the ability to specify the PCB thickness as well. We’re happy to announce that as of today, the PCB specifications step allows you to specify the desired thickness of your PCB. You can specify from 0.2mm to 6.3mm in hundredths of a millimeter increments. Some stackups and layer-counts will have higher minimums due to the inner copper layer thicknesses, but we can now make 2-layer PCBs as thin as 0.2mm thick.
The option appears on the PCB Specification tab of your project, and provides a couple of standard thicknesses for quick selection, or the ability to input a custom thickness of your choosing. Selecting a custom thickness will prevent your design from being panelized with other designs, so minimum PCB area charges will apply, but no additional charges will be added unless you increase the thickness higher than that of the standard stackup for your layer count.
Creating Different Thickness PCBs at the Fab House
Given that we can adjust the thickness of the PCB in hundredths of a millimeter increment, it’s worth noting how the PCB fab actually accomplishes this. Let’s take a 2-layer board for example, with a standard 1.6mm thickness. Our expectation is that the PCB fab has some copper-clad core, with the total thickness of the copper and FR4 material equaling 1.6mm. Now, you probably wouldn’t expect that they’d also have that same core materials in 1.67, 1.68, and 1.69mm thicknesses — and you’d be right.
What are core and prepreg? Core material is an FR4 substrate that has been fully hardened and is pre-plated with copper foil. Prepreg (pre-impregnated) is a layer of epoxy resin that has not been fully cured, with a thin layer of fiberglass embedded in it. To make PCBs out of multiple layers, the prepreg is stacked and then pressed and heated. The epoxy cures fully during this process.
To create custom thicknesses, the PCB fab starts with a set of common prepreg thicknesses, then combines them in the necessary sequence, along with copper foil and solder mask thickness to make the desired final thickness. For example, to make a 0.63mm thick 2-layer PCB, assuming our standard thicknesses of 0.035mm for 1oz of copper pour and 0.01mm for soldermask, you’d need three 180µm prepreg layers – demonstrated in the image to the left.
Our board fab actually builds all boards this way, even standard-thickness 2-layer PCBs, rather than using pre-sized copper-clad cores. This is how we are able to provide custom thicknesses with no additional charges for thinner stackups than our standard displayed stackups. Thicker stackups incur slight additional charges since they utilize more material in the process for a given layer count.