Protecting BGA packages
08 October 2007
Al Lewis, Director of Marketing and Applications at Asymtek, looks at how automated dispensing of edge bonding protects BGA packages
Asymtek’s DispenseJet DJ-9000 valve makes possible corner and edge bonding, two technologies that offer an alternative to underfill for applications where a complete underfill process is not required. They offer an easy-to-use, reliable, and cost effective method for increasing mechanical strength when attaching ball grid arrays and similar chip scale packages. Asymtek is demonstrating these technologies at Productronica.
In corner and edge bonding, the accuracy in the amount and position of applying the fluid directly correlates with the reliability of the bonding process. Although standard surface mount dispensing equipment is acceptable when only a low degree of mechanical reliability is needed, standard SMA equipment is not designed for the type of pattern flexibility and fluid accuracy required for higher reliability; however, that’s exactly what jetting is designed for.
Jetting is an ideal dispensing method for these processes. In corner bonding, adhesives are jetted on the printed circuit board in dots at the corner of the BGA attachment points prior to placing the BGA. When the part is re-flowed, the material cures and provides the necessary mechanical reinforcement to prevent solder joint failures due to shock and bending on the printed circuit board assembly. For edge bonding, the material is applied and cured after reflow, also improving resistance to shock and bending failures. For high reliability, the bonding material must not interfere with the reflow process, therefore it must be placed in the exact position with the correct volume and with the proper shape so that it captures the edge of the package without touching any of the interconnect balls.
For high volume assembly applications, using needles on SMA equipment slows down the process. The more sophisticated dispense patterns required for corner and edge bond reliability make it difficult to keep pace with medium to high volume production typically found in production lines that run at 30,000+ component placements per hour. Jetting eliminates this problem because the jet can accommodate those speeds. The DJ-9000 gives speed improvements of up to 500% compared to traditional needle dispensing.
Asymtek’s automated fluid dispensing equipment has process controls in place to regulate the amount and placement of fluid. Calibrated process jetting ensures that the correct volume of adhesive is jetted and data logging of critical process parameters ensures high yield production.
Using corner and edge bonding instead of underfill offers several advantages. Board heating is not required, eliminating pre-dispense heat and dispense heat stations and potentially allowing for a dispenser with a smaller footprint to reduce floor space and cost of ownership. Materials used for these processes typically is not abrasive, which can relax requirements on wetted parts inside the fluid delivery device, and the material typically has a longer working life, reducing the cleaning and accommodation of rheology changes. In addition, multiple dispensing steps and timing algorithms are not required.
The goal of corner and edge bonding is to improve board assembly reliability at less cost, with fewer process steps, while using less equipment and floor space than underfill. By using automated fluid dispensing equipment with jetting technology and process controls, this goal can be achieved.
Contact Details and Archive...
Most Viewed Articles...