A hairline short circuit happens when there is a chance connection between two unconnected signals. For instance, when a positive connection connects with the signal on the ground, it becomes a short circuit. If thick copper ties the signals, you can easily see the short circuit when it occurs. If you manually build your Printed PCB Circuit Design Boards (PCBs) instead of machine produce them, short circuits occur more.
When you manufacture your PCB by machine, a hairline short circuit is a genuine concern. The reason for this is that thin copper, as thin a hair strand, has the ability to connect two separate signals. You may not detect this kind of short circuit unless the PCBs undergo some QC testing. If you discover a short circuit at this late stage of production, then it causes great losses in energy, time and raw materials.
You have to thoroughly understand the PCB building process to understand how short-circuiting occurs. A PCB’s composition is copper, overlaid on a non-adaptive surface. The most popular method remains to engrave the circuitry on the PCB by using photo engravement. A photoresist coating makes up the PCB, and a laminate consisting of a silk screen holds and covers the circuit image.
The PCB undergoes exposure to ultraviolet light and you use an ammonia-based mixture to remove the parts the silkscreen did not cover. A mistake in the automated procedures could cause a narrow copper line that connects pads or different signal tracks. If the after manufacture tests are not thorough, problems arise later.
You should never assume that the PCB manufacturer has carried out all the required electrical post-manufacture tests. You should always endeavor to pass your PCBs through electrical tests such as the Flying Probe Test before assembly. This Flying Probe Test passes high-accuracy scrutiny over the components to check for manufacturing and design faults and errors.
The electrical testing does not provide a 100% error margin. Hairline short circuits have a possibility of escaping detection in testing. To minimize your risks, make sure your PCB provider encompasses a policy for reimbursement strategy. This ensures you get reimbursement for every PCB that goes through the electrical test and turns out faulty. A good manufacturer with reputation to uphold replaces and reimburses the raw material cost.
As a designer, you also have the responsibility of reducing the probability of PCB faults. You can do this, while also watching your budget or form factor. This is by opting for a bigger gap between the pads and copper connections. No studies exist that link hairline short circuits with the gap between the copper connections. The best way is to avoid maxing out the supplier’s capability. Try to add the tolerance of your clearances in your designs. If for instance, a supplier makes a specification that, the PCB can handle 5-mil clearance and trace width, make sure you set up your design with a clearance of 6. As an engineer, you need to always test the manufacturer’s limit, albeit on a smaller capacity, rather than risk a huge production batch.
Good quality PCB designing software let you set clearance instructions that govern your design check-up before you do production finalization.
