FR-4 Chip Package Pad Structure for Lower-Cost Wire Bonding
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Solution Overview
Problem
The high material costs associated with chip packages made from bismaleimide triazine (BT) resin substrates, particularly due to the use of gold in solder pads, necessitate a cost-effective alternative that maintains structural integrity and precision during wire bonding.
Innovation Solution
A chip package design utilizing a glass fiber substrate made of FR-4 fiberglass with a stacked metal substrate pad composed of nickel, palladium, and gold layers, or a nickel and gold layer stack, providing structural strength and reducing gold usage, while withstanding positive pressure during wire bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a substrate made of BT resin is used, then the substrate can meet requirements for chip package structural integrity, but the material cost of manufacturing is increased
Solution Approach 1:
The patent replaces expensive BT resin substrate with a more cost-effective substrate material that achieves the required structural integrity through optimized metal layer stacking (Ni-Pd-Au or Ni-Au) rather than relying on expensive resin materials. The substrate structure is designed to be functional and durable enough for the application without using premium materials.
Solution Approach 2:
The patent employs composite metal layer structures (Ni-Pd-Au or Ni-Au stacked layers) on the substrate to achieve both mechanical strength and electrical functionality. This composite approach allows cost reduction by optimizing the combination of different metal layers rather than using单一 expensive materials throughout.
2Strength
If a gold (Au) layer with thickness of 0.3-0.4 μm is used for solder pad, then the substrate and solder pad can bear positive pressure during wire bonding process, but the material cost is increased
Solution Approach 1:
The solder pad structure is segmented into multiple metal layers (Ni-Pd-Au or Ni-Au) with specific thicknesses. The total thickness is reduced to 3.15-5.4 μm while distributing the pressure-bearing function across multiple layers rather than relying on a single thick gold layer. This segmentation allows cost reduction while maintaining structural capacity.
Solution Approach 2:
Different metal layers are assigned different functions: Ni layer provides structural foundation, Pd layer offers intermediate protection and bonding, and Au layer provides surface conductivity and oxidation resistance. This local optimization of material properties allows using thinner total material while achieving the same pressure-bearing capacity.
3Ease of manufacture
If the substrate pad is made with less amount of gold, then the material cost is reduced, but the ability to withstand positive pressure during wire bonding may be compromised
Solution Approach 1:
The patent changes the parameters of the solder pad structure by reducing total thickness to 3.15-5.4 μm and optimizing the thickness distribution across Ni, Pd, and Au layers. This parameter optimization maintains pressure-bearing capacity while reducing gold content and overall material cost.
Solution Approach 2:
The Pd layer acts as an intermediary between Ni and Au layers, providing both mechanical support and protective functions. This intermediary layer allows the structure to withstand pressure with reduced total material thickness, enabling cost reduction without sacrificing strength.
Data Source
AI summary
A chip package which includes a glass fiber substrate made of FR-4 fiberglass is provided. The chip package further includes a substrate pad which is a stacked metal structure with a certain thickness and composed of a nickel layer, a palladium layer, and a gold layer, or a nickel layer and a gold layer stacked over at least one first circuit layer in turn. A total thickness of the substrate pad is 3.15-5.4 μm. The glass fiber substrate and the substrate pad can bear positive pressure generated during wire bonding. Thereby at least one solder joint is formed on the substrate pad precisely and integrally. This helps reduction in material cost for manufacturers.