Factors Impacting Bump Solder Extrusion, Failure Mechanism and Methodologies to Improve

Flip chip market is driven by the imminent need for circuit miniaturization, growth in internet of things, big opportunities in data centers and technological superior packaging. With the never ending need for smaller form factors and more & more IOs, bump pitches are getting smaller and smaller. Flip chip packaging with denser and smaller bumps in big packages becomes a challenge. Number of thermal processes also increases in flip chip processing. High layer count substrates added more stress to the bumps and the underfill material supporting the bumps. Bumps are the interconnect between the die and the organic substrate. Bumps are covered by underfill material in order to support the bumps mechanically and also to prevent solder extrusion. Bump solder extrusion is one of the challenging failures to overcome during processing and in the field application. Solder extrusion can happen due to underfill cracks or polyimide (PI) cracks or there is a delamination between underfill and PI, which is coated on the die surface. If the bonding strength between underfill and PI is weak, it can delaminate due to thermo-mechanical stresses during processing or in the field applications. This paper discusses critical factors which impact the adhesive strength between underfill and PI layer, the inputs and parameters required for critical factors and the results.