Wednesday, August 12, 2015

PoP Evolution


PoP is popular package configuration for smartphones, since this format allows integration of AP/baseband logic with DDR(DRAM) in limited space constraints (footprint & height) while maximizing performance (high speed & bandwidth for memory). Over time, has evolved from WB-POP to FC-POP, and now from BD-PoP to MLP-PoP.

Increasing performance requirements drives larger logic die and package body size, thin core or coreless/ETS substrates, all of which increase warpage that make meeting tightening coplanarity requirements, very challenging. Package height constraints further necessitate thin die/substrates that increase coplanarity/warpage concerns.

In addition, higher memory performance drives need for fine pitch memory, that require smaller ball sizes, which translates to smaller collapsed height or clearance between top & bottom packages.

MLP-PoP is an approach that (1) alleaviates above concerns of warpage & coplanarity, by making use of an overmold that adds structural robustness to the package and (2) enables fine pitch memory by improving the clearance between the 2 packages, without needing excessive die thinning.

This may be MLP-ED (exposed die) or MLP-OM (overmold). ED reduces overall package thickness but slightly higher cop/warpage is the resulting tradeoff. Further, this may be MLP-CUF v/s MLP-MUF

However, MLP-PoP requires additional molding processes - and comes at a premium (cost). Lower cost alternative is to use BD PoP with CuBOL for the bottom package, that increases package to package clearance by reducing die-to-substrate standoff.

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