SMTA International Conference Proceedings


Author: Patrick McCall
Company: PACE
Date Published: 9/12/1999   Conference: SMTA International

Abstract: Grid Array packages (BGA and CSP/micro BGA) are gaining in popularity and acceptance in electronics manufacturing because they offer higher I/O counts per unit area and smaller footprints than conventional surface mount components. As grid array (GA) packages continue to gain acceptance, costs will come down, making them more accessible to all manufacturing.

Contract Manufacturers and OEMs are finding that GA devices prove to be more reliable and offer higher production yields than leaded devices. The most common cause of GAs having to be reworked during production is due to IC or other failure, not because of unsuccessful placement or reflow. In informal conversations, several contract manufacturers have reported that when using GAs, the need to rework packages due to bad placement or bad joints has dropped as much as 50 to 60%. In the future GAs will be preferred due to the higher production yields, higher performance and wider functionality. Today, GAs are seen in high end products. As manufacturing costs continue to come down, GAs will become the component of choice in all types of products.

On the surface, the cost of purchasing a rework station for GA components may not appear to be justified as the number of operations (and therefore problematic assemblies) is much lower than when using leaded devices. However, the higher dollar value associated with GAs and related assemblies is significant enough to justify the purchase of GA rework equipment. This, in turn, allows manufacturers to save valuable components and/or board assemblies and realize higher overall yields.

Because GAs are the package of choice for intelligent silicon, rework is often needed for other non-production-related reasons. In many cases, the performance or function of the final assembly can be greatly improved simply by modifying the internal software. Designers often allow for these types of upgrades in assemblies used in communications or monitoring applications. Therefore, the ability to rework a GA allows manufacturers the ability to upgrade or enhance an entire final assembly. When rework is performed for this reason, it is critical to ensure the process is successful and no damage or unnecessary thermal stress is applied to the assembly.

Factors that should be evaluated when selecting GA rework equipment include:

1. System Flexibility

2. Paste Stenciling and Flux

3. Flexibility in Component Placement

4. Full board Pre-Heating Capability

5. Flexible Nozzle Configurations

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