Having worked in the production of PCBs, the debugging of PCBs and the design of PCBs, I can confidently say that Design For Manufacturing (DFM) is often overlooked by professional designers.

In my professional career, I have met some PCB designers who do not know what impact making certain design choices have on the manufacturability of a product. I myself find this quite disturbing. This includes possible rework which would be hard to perform, neglecting certain keepouts, neglecting design guidelines.

When I worked at an SMD production line, I often encountered tombstoning, which is the phenomenon of an SMD passive flipping up like a ‘tombstone’. This phenomenon happens when one side of the applied solder paste on the component has already molten and the other is still a paste. This happens often when a small component is attached to a trace on one side (read: small thermal mass) and attached to a copper plane (read: big thermal mass).

Due to one side being molten, it will stick to the side of the component and pull the component up, lifting one pad of the board. This will create an open circuit and is not how the design was intended (although it can look funny).

When creating a PCB, I only try to use thermal reliefs on those components which are connected to a copper plane on a single side or have a shape similar in size on both sides of the component so that they are less likely to tombstone.

I have had discussions with colleagues who were not aware of how often this can happen, especially on smaller components (read 0402, 0201, 01005).

Luckily, with these thermal reliefs, which makes it so that the component is connected to a shape by two or more traces. It acts like a thermal impedance, which keeps the heat on the pad instead of dissipating it in the copper shape.

Another issue with heat, is reworkability of components. Say, the production plant soldered an N-channel MOSFET to a PCB and it should have been a P-channel MOSFET. Lets swap it out, easy! But what if you connected its drain to a huge copper plane and your soldering iron cannot get it desoldered for the life of it? This issue is often overlooked and once again adds time to your rework process and thus your production process. It also introduces the risk of damaging the PCB by thermal stress.

Adding rework to a process is unwanted, it results in monetary losses, and can lead to more waste and degredation of a product. These are the bane of any production fabs existence. Physical PCB damage by the technician, board delamination, burning the board, ripping traces, but also throwing the board away as a client does not want a reworked board are all things that can be made less common by thinking of the production process when designing a board.

This article might sound ranty/like I know everything, I just want to make the reader think twice about design choices. I also have a lot to learn and want to keep learning.