Low ball BGA: a new concept in thermoplastic packaging (2004)

Area array packaging has advanced to become a vital and enabling technology. It has replaced perimeter-restrictive designs where space efficiency and high performance are important. But this type of package has brought a cost penalty. The package substrate has the highest cost component of the ball grid array (BGA). The problem is how to reduce the cost of the substrate? Now add the challenge of producing a cavity style design for the rapidly expanding MEMS (microelectromechanical systems) and optoelectronics markets. Is it possible to provide a low cost but adequate near-hermetic package that can be manufactured in high volume? This paper discusses the development of a thermoplastic injection-moulded cavity package that may be the most economical design possible. The simplest interconnect is a metal ball, or sphere, in terms of manufacturability, material utilization and cost minimization. But the key is to use the natural spherical geometry for the through-package conductor. Each ball becomes an isolated vertical electrical conduit for both first-level and second-level connections. The balls replace the more expensive lead frames and chip carriers. Non-fusible metal balls extend right through the package housing to create chip bond pads on the inside and a solderable ball grid array on the outside. Assembly becomes the standard SMT process where solder is applied to the PWB and reflowed after packaged placement. The package contains no solder so it is inherently lead-free. The balls, made of copper or nickel with a bondable finish, are insert-molded using a rapid and fully automatic process that could produce hundreds of packages every minute. Our plastic of choice is LCP (liquid crystal polymer) that is widely available and economical, ha a high thermal stability, low flammability, very low moisture absorption and is halogen-free. The package code name is "low ball" for the low embedded ball profile and low cost. The present target is MEMS that requires a cavity, but the design appears suitable for any electronic device including RF and some optoelectronics systems. Once the die is bonded, the final step is to seal a lid made of plastic, metal, ceramic, or glass. We will report work describing lid sealed using a prototype near-infrared laser. Glass lids could allow the package to be used for MOEMS (microoptoelectromechanical systems) optoelectronics and display applications. The low ball package satisfies the growing demand for environmentally friendly components since it is lead-free, halogen-free and has no hazardous materials. There is no production waste since the material for additional packages or other uses. The design could offer easy recycling in the future since materials are reusable. This paper will focus on the simplest design that does not include rerouting or high I/O count. But this is totally adequate for the most common MEMS devices, like accelerometers and gyroscopes that need few connections. However, very high I/O, multichip, 3D and package-stackable versions are possible using our injection molding strategy and will be briefly summarized in future work. This paper will provide details of the low ball BGA, discuss the design sequence, metallurgy, manufacturing, testing, and its current status as a future commercially available package.