Implementing an Effective Solution For Inspecting BGAs

Taking advantage of new technology—in this case, ball grid arrays (BGAs) to replace conventional devices on printed circuit boards (PCBs)—generally requires using more sophisticated inspection equipment. This is especially true for process evaluation and verification and quality-assurance and quality-control applications.
At the Siemens Information Communication Networks facility in Lake Mary, FL, my responsibilities as a senior manufacturing engineer were to define and develop production process techniques, select and qualify equipment, and determine production feasibility as well as production cost-effectiveness with regard to product quality, throughput, yield, and reliability.

My job in determining production feasibility covered a broad range of activities, including materials selection, tooling, test systems, and processes/procedures. Before the BGA project, all of these activities were associated with supporting through-hole and surface-mount technologies for production of densely populated PCBs for the company’s telecommunications products. The division designs and manufactures communications switches and network systems.

When the engineers decided to incorporate BGA technology to replace conventional surface-mount devices, I was asked to determine the feasibility of this approach. There was one major challenge: BGA technology precludes inspection of solder joints with ordinary visual methods.

Definitive Determinations

Without the capability to evaluate the solder-joint integrity of the BGAs, we could not definitively determine their quality or reliability. We knew that we needed an X-ray inspection system to solve the problem.

Our key consideration focused on image resolution. A typical solder ball used in this process is 0.025², and the company’s existing X-ray inspection system wasn’t adequate. The resolution was not suitable for making conclusive determinations about the integrity of a BGA soldered part. Also, use of BGAs places certain demands on X-ray inspection systems including ease of use, flexibility of orientation and precise movement of the PCB under test, and the need for measurement software that provides necessary documentation.

We were aware of many different X-ray inspection systems on the market but were not looking at an automated or digital system, considering it an overkill for our requirement at this time. Also, we did not want to spend $250,000 to $300,000 for it. So, with a budget of less than $100,000 and after evaluating other systems, we purchased a VJ-1000 Analog X-Ray System from V.J. Technologies in Bohemia, NY.

Because BGA solder joints are not visible between the PCB surface and the underside of the mounted components, the new X-ray inspection system can help easily locate critical problems associated with solder reflow, such as voids, collapsed balls, or component delamination. X-ray inspection also helps determine whether BGAs are properly aligned on the board.

Flexibility for Other Uses

In addition to checking solder-joint integrity and BGA alignment, the X-ray system also inspects through-holes on the PCB, another requirement that cannot be accomplished practically with other technologies. The X-ray system permits precise, accurate hole inspection to determine if it is filled with solder for a reliable contact or exhibits voids that ultimately could lead to board failure.

BGAs themselves are relatively easy to place. In fact, once an X-ray inspection confirms that the solder balls are located properly on the PCB, production is robust and relatively straightforward.

Siemens uses automated pick-and-place equipment for much of our large-scale production. BGA technology is easier to work with than quad flat packs. An X-ray inspection system that can quickly ensure there is no problem is vital for this procedure.

Siemens is convinced that BGA technology is the way of the future, especially with regard to the time and costs associated with quad flat packs. After six months of experience with BGA technology, the company is considering using microBGA technology. While the existing 80-kV VJ inspection system will accommodate microBGA technology with its resolution capabilities, a 130-kV system is being considered as an upgrade.

Eliminating the Blooming Effect

One of the key advantages of the X-ray system at Siemens is its capability to eliminate all areas of subjectivity, which previously made it difficult or impossible to provide go, no-go decisions regarding process verification. An example of this is the blooming effect, a phenomenon that occurs when the X-ray energy is too strong (much like an overexposed photo), which prevents accurate interpretation.

To eliminate this phenomenon, the X-ray inspection system provides voltage and current adjustment parameters. It allows inspection of the part through a continuously varying kilovolt (potential) and milliamp (current) field, ensuring that the flaws observed are truly located in the object and not created by blooming or veiling-glare phenomena.

About the Author

Ben Zarkoob, formerly with Siemens ICN as a senior manufacturing engineer, has 16 years of experience in electromechanical, surface-mount technology, and BGA assembly processes. He received an M.S. in industrial engineering and management systems from the University of Central Florida.
Siemens Information Communication Networks, 400 Rinehart Rd., Lake Mary, FL 32746, 407-942-5000.

Published by EE-Evaluation Engineering
All contents © 2000 Nelson Publishing Inc.
No reprint, distribution, or reuse in any medium is permitted
without the express written consent of the publisher.

October 2000

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