Manufacturability Assessments Of Board Level Adhesives On Fine Pitch Ball Grid Array Components
Authors: Venmathy Rajarathinam, James Wade, Alan Donaldson, Raiyo Aspandiar, Devadoss Chelladurai, Scott Mokler Company: Intel Corporation Date Published: 10/13/2013
Abstract: Board level adhesives, such as underfills and corner glues, have gained acceptance as a method of mitigating issues related to the mechanical reliability of ball grid array components. Manufacturability requirements of such materials need to be considered as a major factor in their selection. The primary characteristics that reflect the suitability of underfills and corner glues for manufacturability include flow time, ability to rework the adhesive and cost. This paper will review the flow and rework characteristics for various board level underfills and corner glues across the range of available material properties. Relationships between key material properties and their manufacturability will be established. These parameters include the coefficient of thermal expansion (CTE), glass transition temperature (Tg) and storage modulus (E`) of the material. Results indicate that E` and Tg have a significant impact on rework yield. The ideal material properties for rework are low E` and low Tg. Additionally, reworkability is not directly dependent on CTE and therefore the presence of fillers is not detrimental to the rework process. However, the presence of fillers does increase flow-times for packages with underfill, but dispense conditions can be optimized to modulate flow times. To further increase manufacturability, the filler loading should be tailored to achieve product reliability targets.