Printed Circuit Boards or PCBs for short are manufactured with utmost care and to specific designs. Though they are generally reliable, there are times in which errors can happen in the construction process, rendering them faulty. For maintenance issues or otherwise, there may be a need to repair the PCB. A basic understanding of electrical circuits and how they are implemented in the PCB design is essential for PCB repair service.
At the very basic level we all know that there are two types of electrical current — alternating current (AC) and direct current (DC). AC current is in the form of a curve, or sine wave, while a DC current is in the form of a straight line. These days almost all electrical appliances use PCB. Modern PCBs are manufactured with more advanced design methods and processes and are less prone to error. Today’s PCBs contain copper, fiberglass substrate, silk screen and solder mask. Contemporary PCBs consist of multiple layers necessary to house complex circuitry making PCB repair service a tougher process.
The diagnosis, repair and troubleshooting of modern PCBs have become tougher as numerous high-pitch parts are not identified on the boards. Boards of the previous decades were easy to repair with the use of automated testing tools, which no longer work on modern PCBs. Therefore, the trouble-shooting logic varies greatly with the PCB generation.
On old PCBs trouble shooting was performed through inspection of joints (soldering), inspection of ICs testing the functionality, troubleshooting specific components and parts, prone for frequent errors and consultation with software manual. As a majority of these tests and procedures are ineffective today, modern PCB repair service requires a much more complex analysis.
Before actually latching on to the repair work on a printed circuit board, we must identify the root cause of the problem. Diagnostic work follows thereafter.
Identification of the problem:
The problem is identified with the use of a VI instrument. The alternating voltage is used to test the unidentified pin count. The location of the problem is then identified with a microscope. Finally, the faulty component is removed from the circuit board, and replaced with a functional one.
In electrical circuits the electrical components are generally arranged (connected) in Mixed, Parallel or Series connections. The easiest way to find the signature or analyze is to compare the faulty PCB with a functional PCB of the same make/model. For comparison, the similarities between all defective PCBs should be examined and compared and contrasted with functional PCBs. The current, inductance, voltage and resistance etc., should be computed and contrasted to determine what’s wrong.
While attempting repair, any deposits of partially worn off solder should be removed. The examination and dust removal process itself should be done with care as there is a possibility that certain tracks may incur damage. Each pin is tested for proper output/input.
The following is the sequence of steps to fix the PCB.
Clean the affected part of the PCB with isopropyl alcohol. Dry excess alcohol with compressed air.
Use an Exacto knife to peel off the damaged pad, gently.
Remove any burnt laminate in the area and eliminate any residual solder mask on the conductor.
Wipe the spot with isopropyl alcohol and dry with compressed hair. You can also clean the spot with a lint-free cloth.
Hold the solder alloy in hand and prepare the conductor area, for replacement fixing.
After choosing your new conductor, remove your selection from the circuit frame with a small knife.
Cover the spot on the new conductor that will face the old trace and prepare your epoxy. It is best to prepare only small portions at a time. Apply the epoxy mixture to the printed circuit board. To speed up the bonding process, place in open air. You can also cure the joined pieces in an oven.
Using Kapton™ tape, place the new conductor in its place.
Clamp the new pad in its spot and allow it to cure.
PCBs were traditionally tested by visual inspection, x-ray imaging and burn-in. The above procedures may be useful in the production line, as they only provide for physical inspection. They can identify a fracture/crack, missing component, incomplete solder etc. But they are ineffective when diagnosing problems such as an electric short circuit, bad transistor or heating components etc. These cannot be identified by visual examination and in such cases, thermal images are very useful. Thermal image analysis relies on the power dissipation of each integrated circuit (IC) on the PCB. Thermal or heat management is one of the critical problems facing electronic manufactures. Thermal characteristic of electronic components is captured by an infrared camera and thermal image is achieved. This thermal image can be used in the testing process of PCB. The deviation from normal thermal dissipation pattern is a sign of faulty occurrence.