PCBs PCBs: top troubleshooting tips
Hailed as the lynchpin of electronic equipment, printed circuit boards (PCBs) are at the heart of everything that requires some form of electric function. As technology advances, so demand for PCBs will grow as reliance on them increases. PCB failure can happen for various reasons during manufacture and use. It is important that these problems are detected and repaired to minimise waste and reduce costly product recalls. Whether you are an OEM or an assembler, it is perhaps inevitable that you may have encountered PCB assembly faults at some point. Marc Ellis, managing director at CEM and PCB assembly specialist UK Circuits, looks at the eight most common assembly problems most likely to occur and what can be done to help prevent this from happening or occurring on any future boards
1. Problem: Solder bridges As one of the most common problems, solder bridges, also known as shorts, can be extremely hard to pick up as they can be miniscule in size. If this fault goes undetected, it can lead to a short circuit as well as serious damage to the component or board, such as a component burn-up or blow-up and/or burn-out PCB damage. Reason: Solder bridging can occur when two points on the circuit board which should not be electrically connected are inadvertently connected by solder during PCB soldering. These may be between adjacent pads, traces and pads or traces close together. This can happen if there is an insuffi cient solder mask between pins.
Conversely, it can occur due to the excessive application of solder between joints or using soldering tips that are too big or too wide. Prevention: This can be dealt with at the design stage through refi ning weight distribution and alignment of components.
2. Problem: Clearances Copper, used as an active component of PCBs, is an extremely conductive metal. It is also relatively soft and vulnerable to corrosion. To prevent this and protect the copper from interacting with its environment, other materials are used to cover it. Reason: When a PCB is trimmed, if the copper is too close to the edge, part of this coating can also be trimmed, causing
copper exposure and insuffi cient copper to edge clearance, which can lead to shorts. Clearances can lead to the board being damaged as well as numerous problems in the functionality of the board. Prevention: This issue can easily be avoided by making sure that the minimum clearances for the specifi c type of board being fabricated is adhered to.
3. Problem: Plating voids Plated through-holes are copper-coated holes in a PCB, enabling electricity to flow from one side of the circuit board to the other. When these holes are drilled through, a layer of copper is then added to the surface of the material and along the walls
of these holes through an electroplating process, which entails a thin layer of electroless copper being deposited onto the circuit board, with extra layers of copper then being added and etched to create the circuit image. Reason: When copper on the inside walls of the PCB holes isn’t suffi ciently plated, it can result in voids in the plating, which prevents the electrical current to pass between the layers effi ciently, resulting in a defective product. Prevention: This can be prevented by ensuring that the holes are thoroughly and properly cleaned after drilling, in order to avoid any contamination of the material or air bubbles inside.
42 March 2023
Components in Electronics
www.cieonline.co.uk
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