3D and 2.5D packaging assembly with highly silica filled One Step Chip Attach Materials for both thermal compression bonding and mass reflow processes

One Step Chip Attach (OSCA) materials are chemically engineered organic fluids that function both as underfills and fluxes for flip chip assembly. These emerging materials chemically remove solder oxides and surface finishes to facilitate soldering during reflow while simultaneously curing to form a rigid reinforcing polymeric underfill that improve the reliability of the finished product. The key advantage of OSCA is a reduction in the number of steps in the assembly process, which naturally results in faster cycle times and more efficient flip chip assembly. With suitable chemistry, fillers and the correct filler loading, OSCA materials are dispensable and capable of achieving high yield and reliability. OSCA materials may be designed for use in thermo-compression bonding (OSCA-T) and in more standard mass or gang reflow (OSCA-R), the choice of process depending on the package functionality and design requirements. This paper shares information on the properties and processing techniques of OSCA materials and explores the assembly data concerning control of solder wetting, over collapse, voiding, and HAST behavior. Data will be presented from testing at the material level and from testing of micro bumped lead free Silicon to Silicon vehicles designed to simulate chip to wafer or chip to chip bonding. Challenging loadings of up to 65% silica with distributions as low as 0.5 micron average particle size will be shown at both the assembled and material level.