Assembly Yields Characterization of High IO Density, Fine Pitch Flip Chip In Package Using No-Flow Underfill

High IO density and fine-pitch devices characterize the modern electronics demands on Flip Chip in Package (FCIP). Increasing demands in FCIP are driving IO counts in the 1000 to 5000 range and bump pitches down to 125um. Such devices inhibit the effective processing of capillary flow underfills. This work investigates the use of no-flow underfills as an alternate to capillary flow materials for these high density interconnect systems. This paper represents an experimental study on high yield processing for IO density and fine pitch FCIP devices using no-flow underfills.

It is show that high yields can be obtained under optimized assembly process conditions. Optimized flip chip assembly parameters depend on underfill material characteristics and the device interconnect configuration. Since process performance of commercial no flow underfills was limited on the high IO density test vehicles, newly developed underfill materials from commercial suppliers were considered for this production test vehicle. New methodologies are explored to better narrow the feasible process conditions for establishing process conditions promoting high yield.

Experiments were conducted to investigate material thermal limits, outgassing characteristics, reflow profile parameters, and void formation factors using a parametric approach and design of experiments. AATC Reliability tests will be performed. Failure mode analysis will be performed using acoustic microscopy and cross sectioning.

This research provides a systematic development of optimal process parameters for high IO density, fine pitch FCIP. Reflow time and peak temperature were proved dominant factors for high yields process based on research using high IO devices. While high value in both reflow time and peak temperature is essential to achieve high yields process, too excessive high number also can cause outgassing which can be reason for yields loss.

Regarding void phenomena, reflow time is the most significant parameter for formation based on void formation study. It can be the reason of yields failure due to complex no-flow underfill curing mechanism. The parametric studies and DOE show how the limit of reflow parameters can be examined and decide optimal number to setup high yields process.