Wafer Level Package Redistribution Layer Interposer
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Solution Overview
Problem
The miniaturization of semiconductor dies increases the difficulty in packaging due to higher I/O pad density, and existing wafer level packaging methods face challenges with known-good-die loss during post-molding thermal processes.
Innovation Solution
A semiconductor package with a redistribution layer interposer and a method that involves forming a passivation layer, dielectric and metal layers, ball pads, and applying a molding compound after forming an under-bump metallization layer and solder bumps, which reduces the risk of known-good-die loss by sequencing thermal processes differently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If post-molding thermal processes are applied to the wafer level package, then the packaging structure is completed, but the risk of known-good-die loss increases
Solution Approach 1:
The under-bump metallization layer and solder bumps are formed on the ball pads before the molding compound is applied. This preliminary formation of critical interconnection structures allows the thermal processes to be performed after molding, avoiding exposure of completed solder joints to high temperatures that would cause die loss
Solution Approach 2:
The conventional sequence is inverted: instead of forming under-bump metallization and solder bumps after molding, these structures are formed before molding. The molding compound then encapsulates these structures, protecting them from subsequent thermal processes and eliminating the risk of known-good-die loss
2Quantity of substance
If semiconductor dies are miniaturized to increase I/O pad density, then the functional requirements are met, but the packaging difficulty increases
Solution Approach 1:
The ball pads are formed in the first passivation layer on the front surface of the interposer, while the under-bump metallization and solder bumps are formed on the rear surface. This spatial separation across different dimensions and surfaces allows independent processing of high-density pad arrays without increasing packaging complexity
Solution Approach 2:
The interposer structure is segmented into multiple functional layers: first passivation layer with ball pads, RDL for signal redistribution, second passivation layer for protection, and rear-side under-bump metallization with solder bumps. This segmentation allows each layer to be optimized independently for its specific function, managing the complexity of high-density packaging
Data Source
AI summary
A semiconductor package includes a redistribution layer (RDL) interposer having a first side, a second side, opposite to the first side. The RDL interposer comprises a first passivation layer, at least one dielectric layer on the first passivation layer, a metal layer in the at least one dielectric layer, a second passivation layer on the at least one dielectric layer, and a plurality of ball pads in the first passivation layer. At least one semiconductor die is mounted on the first side of the RDL interposer. A solder mask covers a lower surface of the first passivation layer and exposes the plurality of ball pads through a plurality of openings in the solder mask. An under-bump mettalization (UBM) layer is disposed at a bottom of each of the plurality of openings. A solder bump or solder ball is disposed on the UBM layer in each of the plurality of openings.