When it comes to PCBs, there is an essential step that often goes ignored. We are usually so occupied with the design, application and components & their placement that we forget about the most important element of the PCB i.e. the Bare Board. As discussed in our previous blogs, we run extra tests or are extra cautious to ensure the proper placement of the components but shouldn’t we cross-check the Bare Board for any defects?

A Bare Board refers to the state of the PCB consisting of the substrate, metal coating, conductive pathways and patterns but not electronic components or through holes. In simple words, it is a printed circuited board without any components on it. To check for any defects such as opens (over etchings), shorts (under-etchings), and holes, a bare board needs to be tested. It is done prior to attaching any components. This is tested in two stages:

• Isolation Testing: It involves checking the stability between interconnected pads. Verifying that the required resistance between two separate electrical connections is met.
• Continuity Testing: It checks for complete isolation between individual circuit patterns so that there are no open points within the circuit.

Methods of Bare Board Testing:

Either of the two methods is used for Bare Board Testing.

• Pinned Fixture Test: Spring-loaded pogo pins are used to test the board’s connective surfaces. Pressure is applied through the top and bottom plates to ensure the connection. It has proven to be an efficient method as it is capable of testing multiple points at the same time, saving time and energy. Also, it doesn’t take only a few seconds to perform the test once the pins are fixed.
• Flying Probe Test: two robotic arms equipped with poles, guided by software instructions are used to verify the board’s connectivity. The flying probes travel across the board testing various connections. It may take longer than the Pinned Fixture Test but is a comparatively more flexible and affordable option.

Importance of Bare Board Testing:

It is important to test a Bare Board for any defects that may disrupt the PCB functioning. It helps ensure the reliability of the PCB. It is important to know that your bare PCB is solid before you start soldering expensive components on top of it. Especially if you’re dealing with SMTs and fine line mounting technologies.

While it may seem to be a task, but investing some time, money and effort into bare board testing can save you time and money in the longer run by avoiding field testing, repair, and maintenance costs further down the line. So make sure to test your Bare Board to avoid further regrets.