Interposer Substrate Immersion Tin Surface Processing
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Solution Overview
Problem
Conventional interposer substrates face issues with surface processing layers, particularly with organic solderability preservative (OSP) and nickel barrier problems, which lead to poor reliability and difficulty in controlling intermetallic compounds, especially when solder pads are exposed for extended periods, such as in land grid array (LGA) products.
Innovation Solution
The use of an immersion tin layer as a surface processing layer, which eliminates the need for multiple processing steps and reduces nickel barrier issues, allowing for improved control of intermetallic compounds and enhanced product reliability by forming the immersion tin layer on the exposed surfaces of the wiring and conductive pillars.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OSP (organic solderability preservative) is used as surface processing layer, then solderability is improved, but reliability deteriorates when solder pads are exposed for extended periods
Solution Approach 1:
The patent changes the material parameter of the surface processing layer from OSP to immersion tin (Sn), which fundamentally alters the chemical and physical properties of the surface layer. This material substitution enables the solder pads to maintain reliability during extended exposure periods, solving the contradiction between solderability and long-term durability.
2Ease of manufacture
If multiple surface processing processes are performed (OSP and ENEPIG or Ni/Au), then surface processing completeness is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the complex multi-step surface processing sequence (OSP plus ENEPIG or Ni/Au) and replaces it with a single immersion tin plating step. This simplification maintains complete surface processing functionality while dramatically reducing process complexity and eliminating resist material precipitation issues.
Solution Approach 2:
The immersion tin layer serves multiple functions simultaneously: it provides solderability, acts as a barrier layer, and serves as the final surface protection layer. This multi-functionality eliminates the need for separate OSP and ENEPIG/Ni/Au processes, reducing overall device complexity while maintaining manufacturing effectiveness.
3Manufacturing precision
If nickel barrier layer is used, then intermetallic compound control is improved, but nickel barrier problems occur
Solution Approach 1:
The patent changes the material parameter from nickel barrier layer to immersion tin (Sn), fundamentally altering the metallurgical interaction at the interface. This substitution eliminates nickel-specific barrier problems while maintaining precise control over intermetallic compound formation through the tin-based interface, which exhibits more favorable and predictable intermetallic growth characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This simplifies the fabrication process and enhances the reliability of interposer substrates by providing a suitable surface processing layer for products with exposed solder ball pads, improving the control of intermetallic compounds and ensuring stable performance in applications like LGA and BGA products.
Implementation Method 1
forming an immersion tin layer on the exposed surface of the first wiring layer and the end surfaces of the second conductive pillars
Data Source
AI summary
An interposer substrate includes a first insulating layer having opposite first and second surfaces; a first wiring layer formed in the first insulating layer, with a surface of the first wiring layer exposed from the first surface; first conductive pillars formed in the first insulating layer; a second wiring layer formed on the second surface; second conductive pillars formed on the second wiring layer; a second insulating layer formed on the second surface and covering the second conductive pillars and the second wiring layer, with end surfaces of the second conductive pillars exposed from the second insulating layer; and immersion tin layers formed on the first wiring layer and the end surfaces of second conductive pillars. The immersion tin layers are used as surface processing layers to be applied to products having ball pads that need to be exposed extensively. A method for fabricating the interposer substrate is also provided.