Memory Module Pad Plating for Corrosion-Resistant Compression Mounting
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Solution Overview
Problem
Existing memory modules, particularly those with low power compression attached (LPCAMM2) specifications, face issues with corrosion at the rear surface connection pads due to limited thickness of gold plating, which is prone to corrosion from environmental substances.
Innovation Solution
The memory module design incorporates a three-layer structure for rear surface connection pads, with copper, nickel, and gold layers, and an outer edge dummy layer, along with a solder resist, to enhance corrosion resistance. The gold layer is thickened to 0.7 μm to 3.0 μm using a hard gold plating process, and the solder resist covers the sides and upper surface of the pads to prevent corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electroless plating is used to form the rear surface connection pad, then the manufacturing process is simple, but the gold plating thickness is limited and corrosion resistance is poor
Solution Approach 1:
The connection pad structure is segmented into multiple functional layers: a thick copper base layer (10-20 μm) for structural support and conductivity, a nickel intermediate layer for adhesion and barrier functions, and a gold surface layer for corrosion resistance. This segmentation allows each layer to optimize its specific function rather than relying on a single thin gold layer
Solution Approach 2:
The gold plating thickness parameter is changed from the conventional thin layer (0.05-0.1 μm) to a substantially thicker layer (0.7-3.0 μm), fundamentally changing the corrosion resistance capability. Additionally, the copper layer thickness is optimized to 10-20 μm to provide sufficient mechanical strength and electrical conductivity
2Reliability
If the gold plating thickness is increased to improve corrosion resistance, then the reliability improves, but the manufacturing cost and process complexity increase
Solution Approach 1:
A copper layer is formed on the connection pad before gold plating, creating a substantial base (10-20 μm) that reduces the need for extremely thick gold plating to achieve mechanical strength. This preliminary copper layer allows the gold layer to focus on its primary function of corrosion resistance rather than also providing structural support
Solution Approach 2:
The connection pad uses a composite structure of copper-nickel-gold layers, where each material contributes its superior properties: copper for conductivity and mechanical strength, nickel for adhesion and oxidation resistance, and gold for corrosion resistance. This composite approach achieves superior overall performance without requiring excessive thickness of any single layer
3Reliability
If a multi-layer metal structure is used to enhance corrosion resistance, then the reliability improves, but the manufacturing precision requirements increase
Solution Approach 1:
The gold plating thickness is changed to a substantially thicker range (0.7-3.0 μm) compared to conventional thin plating (0.05-0.1 μm). This parameter change provides a larger process window and tolerance range, making it easier to control thickness uniformly and achieve consistent corrosion resistance without requiring extremely precise manufacturing control
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
The enhanced design significantly reduces the risk of corrosion from environmental substances, improving the reliability and durability of the memory module.
Implementation Method 1
the rear surface connection pad is generally formed by performing gold plating by using an electroless plating
Data Source
AI summary
A memory module includes a module substrate, and a memory device on a front surface of the module substrate, wherein the module substrate includes a plurality of insulating layers, a plurality of rear surface connection pads, and an outer edge dummy layer on the plurality of insulating layers, wherein the plurality of rear surface connection pads include a first metal layer, a second metal layer, and a third metal layer, wherein the first metal layer includes copper, the second metal layer includes nickel, and the third metal layer includes gold, wherein the outer edge dummy layer extends along an outer edge of the rear surface of the module substrate, and wherein the plurality of rear surface connection pads are in contact with a plurality of connector pins in an external compression mounting connector, respectively.