Advanced Rework Technology for Large Area Arrays

Brian Czaplicki
Air Vac Engineering Co., Inc.
Seymour, CT

BGA Rework is now largely mature, although new supplemental processes that provide improved process control such as Solder Paste Dipping and Non-Contact Site Cleaning can now be integrated into existing processes if the rework technology that is used allows.

So what are the next set of challenges that will need to be addressed in regard to Area Array and SMT Rework?

The International Electronics Manufacturing Initiative has recently published its 2013 Technology Roadmap for the global electronics industry which includes a section dedicated specifically to rework and repair.

Of particular interest and importance is the International Electronics Manufacturing Initiative's gap analysis which identifies future specific gaps and challenges that will result from such factors as government regulations, disruptive technologies and new product requirements.

This paper will review five of the key rework gaps and challenges identified including:

1. Reworking very large, next generation area arrays on large high thermal mass assemblies.

2. Development of hand soldering processes for reworking 01005 components.

3. Development of industry-standardized processes for reworking Package-on-Package devices.

4. Development of industry-standardized processes for reworking Quad Flat, No Lead devices.

5. Development of site redressing processes that prevent lifted pads, solder mask damage and copper dissolution.

This paper discusses the five rework gaps and challenges including identification of the key technical process challenges, outlining in detail the efforts-to-date aimed at addressing these new challenges as well as the next steps required for complete resolution of these challenges.

Large area arrays, less than 50 millimeters, on large, high thermal mass PCB's will create rework challenges including meeting the current strict reflow and package temperature guidelines that were established for much smaller BGA's.

Other challenges that will need to be addressed include alignment capability, warpage, large board handling and safe, fast, effective site cleaning.

Access to next generation large area arrays on high thermal mass PCB's is required to develop effective rework solutions.

Methodologies must be developed for reworking microscopic 01005's in a cost effective, practical manner than provides high throughput capability.

The ability to clean the site and prepare it with solder paste will be important as 50% of 01005 defects are created by the paste printing process.

A "Man" Machine Rework Interface approach was proposed as a possible solution.

Packaging innovations such as Amkor's TMV PoP will help resolve Head in Pillow issues that are found frequently with current PoP packaging technology.

A PoP solderability study showed that manual flux application and the use of nitrogen yielded the best results.

Several MLF/QFN solder paste application methods were discussed including two new and innovative methods: stay-in-place stencils and the multi-up stencil.

The design of the stencil for the center pad area is critical to minimize voiding caused by flux entrapment from the low package stand-off height.

Modifications to existing BGA rework equipment as well as new equipment and processes will be required to meet the challenges associated with reworking next generation SMT applications.