Considerations for Reduced Cost Micro Array Component Rework
This article is based on an original publication by Metcal.
Designed to offer high yields with substantial space savings, micro ball grid array packages (µBGA) are quickly evolving into the package of choice when designing new PCB assemblies. Rework due to process or design errors requires the removal of components, and factors including excessive heat, improper removal, and potentially harmful cleaning techniques must all be considered to ensure sound rework practices.
Advantages to µBGA Packages
- Higher Input/Output Density. As PCB size continues to grow smaller, the need for improved input/output density increases. The µBGA offers several times the I/O density per square inch over a traditional BGA.
- Mechanically Strong Design. Developed to reduce component packaging costs and defect rates, the µBGA can be handled without threat of bending or misaligning leads.
- Rigid Placement Tolerances. While standard BGAs are more accommodating in terms of placement accuracy, the µBGA ensures more accurate placement thanks to decreased ball size and lower pitch.
- Direct Thermal Path. Reducing thermal resistance of interconnection and minimizing the likelihood of damage, a land grid array (LGA) offers a direct path for heat dissipation into the board.
- Ease of Stencil Printing. The LGA makes stencil printing a rework necessity, as components are supplied without solder - thus an LGA stencil plate must be created to match pattern and rework machine requirements.
Likewise, there are disadvantages to µBGA and LGA packages, such as time-consuming solder joint integrity X-ray inspection. Additionally, signal trace routing complexity on the PCB increases cost of the board. And, despite high first-pass yields, defective solder joints still occur and result in a more involved rework process.
µBGAs and LBAs mandate more accurate placement thanks to decreased ball sizes and finer pitches, and generally a machine with a placement accuracy of 1 mil is necessary. Use of lead-free solder may present other issues including a decrease in self-centering during reflow.
Process control is particularly critical during the reflow process, as poor procedure can damage the component or board. However, component placement can be easily corrected through repetition. Equipment should provide the necessary level of balance between process control and ease of operation, and it is essential for operators to be properly trained and able to identify defective components.
The same benefits that make the µBGA more attractive in the assembly arena also carry through to the rework process. Ease of solder or flux deposition and ease of alignment simplify µBGA rework in comparison to fine-pitch QFPs. With availability of high-quality and lower-priced convection array rework systems on the rise, users will continue to reap the benefits of a user-friendly system with enhanced technology and process control.