Printed circuit boards (PCBs) have applications in nearly every electronic device available on the market. As the brains of these devices, PCBs are intricate systems that require highly specialized manufacturing processes.
Today, thanks to the recent surge in small electronics such as smartphones and ultralight laptops, PCBs are becoming more compact, intricate, and expensive than ever before. This means that the manufacturing process has become more important than ever. Manufacturers can’t afford to simply repair or replace the expensive PCBs that are in such current high demand.
Manufacturers must ensure that they can detect any defects or contaminants as early as possible with the development process. To do this, PCB manufacturers have come to implement a variety of quality control mechanisms. Some may follow the tedious, but effective method of checking each PCB after every stage of manufacturing, while others choose to inspect them after the entire process is complete. Some approaches work better than others, but all have their tradeoffs. These are some of the most common and effective PCB failure analysis tests that manufacturers use today.
The solderability of an item measures how effectively solder will attach to its surface. Clearly, this is vastly important to know when manufacturing PCBs. If the solder points holding the PCB together are weak, this will shorten the PCBs lifespan or cause it to immediately fail.
The problem is that, often, simple procedures such as storing components for long periods of time can negatively affect their solderability. Many PCB manufacturers test the solderability of each stockpile of components they use, as a means of ensuring that one batch hasn’t gone bad. It’s a good idea to set a benchmark and only use components that exceed it.
This will ensure a baseline level of acceptable quality for all solder contacts. With regard to this approach, if solder points fail, the problem likely originated elsewhere. This method is also useful for determining what actions, if any, could have been causing the solderability problems on the unused components in the first place.
While microsection analysis is one of the most popular failure analysis methods, it is a time consuming and destructive process. Essentially, a manufacturer will use a saw to cut out the portion of a PCB to test it. That portion is then encapsulated in a clear epoxy resin. This resin is then sanded and polished, giving an inspector a clear view of the PCB once it is “floating” in the hardened resin. The inspector can then place the PCB under a microscope and thoroughly examine it for defects, shorts, and more.
One of the main causes of failure in PCBs is contamination during the manufacturing process. Contamination can come from human contact, dust, and even microscopic particles in the air that find their way onto the PCB. These unwanted particles cause the most damage during the chemical reactions that are used for PCB manufacturing; for example, during etching or soldering.
To ensure that there is no contamination before these processes take place, PCB manufacturers use a number of different cleaning methods. Obviously, it’s impossible to easily check whether the cleaning process is completely effective, which is why contamination analysis is vitally important.
After a cleaning, an inspector will submerge a PCB into a solution. This solution will dissolve any contaminants that may be present on the PCB. The inspector can then perform tests on the solution to determine if any material was dissolved during this process.
Thanks to its cost effective application, optical analysis is widely used throughout the PCB industry. In its simplest form, optical analysis involves placing a PCB under a powerful microscope and manually checking for any defects. Inspectors can visually check solder joints, component quality, connections, and more.
With the use of this method, inspectors can quickly and cheaply check known failure points in hundreds of samples. However, sometimes the human eye isn’t enough. Scanning electron microscopes (SEMs) are able to scan PCBs at incredible levels. Some systems operate at more than one hundred thousand times magnification. This allows them to scan areas as small as a few nanometers. The SEM will then produce a large, 3D model of the scanned area for the inspector to thoroughly analyze.
The problem with many of the testing methods listed above is that they can only reach the PCB’s surface. Often, PCBs have vital components and connections that aren’t visible from the surface. This is where x-ray technology comes into play. X-rays are non-invasive, meaning that inspectors can test as many PCBs as possible without worrying about destroying them in the process.
More importantly, inspectors can use traditional or 3D modeling x-rays to test the internal mechanisms of PCBs. They can inspect all of the internal layers for etching and/or alignment defects as well as lamination problems caused by particle contamination. Additionally, with x–rays, inspectors can also view the strength of soldering connections hidden under their components.