Ball grid array or as they are commonly known as BGA is a type of chipset packing used for mounting components in the surface of a PCB. It can provide multiple pins to be soldered within a small area. These pins are commonly regarded as interconnections. BGA is usually used to mount microprocessors, permanently on a circuit board. There can be instances when these components or the interconnections fail. Such a situation demands complex repairs to be carried out at the BGA site.
The Arizona based PCB manufacturer, MJS Designs, explains how to effectively repair or rework a BGA. These easy to follow 3 steps can ensure a quality rework.
1. Detection Of Flaw
The very first step for any repair is the detection and identification of the fault. There can be more than one BGA on a single circuit board. Identification of the faulty BGA can be an unpleasant task. This process is carried out by passing signals through every interconnection and conforming with the output. If there is even the slightest variation between the received output and the ideal value, the BGA may be declared faulty and sent for further processing.
2. Selection Of The Correct Stencil
Once the fault has been detected, the component is removed from the board. This is done by creating a thermal profile of the area to be repaired. Once the component has been removed and cleaned, a new layer of solder paste is applied over the area using a stencil. There are primarily three options for stencils to used while laying solder paste:
- Metal Mini Stencil: This stencil is rigid and offers very less functionality to the technician. The area to be layered should be regular and plane. Also, the required skill level of the technician is very high.
- Flexible Polymer Based Mini Stencil: A more flexible solution to the areas where there are irregular surfaces and the component needs to be compactly mounted, polymer-based stencils are used. With excellent print registration accuracy and site access, these stencils can be disposed of after a few applications. Also, the skill requirement for the technician is very low.
- Print-On-Component Stencil: This type of stencil is typically very expensive. With excellent print registration accuracy but limited site access, this type of stencil needs handling care during insertion and clamping on to the board. The apertures need careful cleaning between uses.
3. Inspection Of The Rework
Now that the component is mounted once again, it is time for inspection. The bga repair can be a tedious job, as there are hundreds of interconnections in a single BGA, typically. Therefore a close thorough inspection is needed. The inspection can be carried out either manually by an experienced inspector, or by using an automated optical inspection machine, or lastly with the help of an x-ray. Each interconnection is checked for its desired output against a prompt input. Once the output value is desirable as per the component programming, the repair work of the BGA is concluded.
Although repairing a BGA could be a tiring job, but ensuring these checks can help with improving and maintaining top-notch product quality.