PCB Rework
Quite unluckily, PCB rework is part and parcel of assembling any regular PCB. There is almost always room for improvement in manufacturing processes that are pressed for time. Driven by economic constraints, today, even though PCBs are more complex than ever before, they still retain their quality of being able to get repaired.
Yes, it is challenging to repair damaged circuit boards – BGA, high pitch components and multiple layers contributing in increasing the difficulty level of the PCB rework, but intricate modern procedures assist in preventing the boards from being thrown in the junkyard.
Here are some of the PCB rework procedures that are crucial in repairing them:
1. Soldering Procedures
For precision PCB soldering, soldering irons with a huge variety of soldering implements of different tips are required. One of the leading reasons for the failure of equipment is faulty soldering. Higher reliability of soldering is attained by:
• Using adequate solder wire (either 63/37 type or 60/40 type for hand soldering).
• Proper application of the solder so that the molten state penetrates through the copper surface to form a metallic bond – this is called wetting.
• Removing the oxide film and contamination around the copper surfaces is an important part of PCB soldering for wetting to occur which can be done by cleaning through flux.
• Controlling the heat.
It is also important to choose a solder mask. Besides green, there are many other options available. For example, a black PCB board has zero contrast and is the best board for mounting LEDs.
2. Component Removal Methods
Placed a component in the wrong position or direction? Well, then you will need to remove these components. A large array of specialized tools is used to remove the components efficiently and securely. However, the tip of the tools should be selected carefully. For conductive, hot air and vacuum desoldering tools, use small tips that cover the component, its contacts and leads completely.
Through-hole components can be removed by using either a powered vacuum tool for desoldering or solder fountain system. Surface mounted (SMT) chip components are often glued by epoxy to the board. These can be removed by forked tip which can easily fit over the top portion of the chip. Another commonly used method for removing SMT chips is by placing hot tweezer tips over the components. Hot gas/air and conduction methods are used to remove surface mounted Gull wing and J lead components.
3. Conductor Repair Methods
PCB wiring is another area which might be in need of rework. If a circuit gets lifted, liquid epoxy is placed beneath and around the lifted circuit. It is then pressed downwards to bind it again to the PCB. Drey film epoxy of appropriate thickness is also used to cater to the lifted and damaged circuits. Missing circuits and damaged PCB wiring can be repaired by circuit tracks (of dimensions equivalent to the missing circuit) and insulating it with epoxy. Non-insulated wires, welding and adhesive tapes are also used to repair damaged wiring.
4. Base Material Methods
At times, the PCB’s base material may also be in need of rework. This type of a PCB rework is used to repair delamination, blisters, holes, key, slots, bow and twists. PCB milling is done in key and slot repair through epoxy and transplant methods.