Pd-P Alloy Interlayer for Ceramic Substrate Wire Bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for forming ceramic substrate parts with wire-bonding electrodes face issues such as nickel plating layer corrosion and palladium diffusion to the gold layer, leading to poor wire bondability and reliability, especially when using high-density mounting and lead-free, high-melting-point solders.
Innovation Solution
A ceramic substrate part is developed with a structure comprising a primer layer, a Ni-based lower layer, an intermediate Pd-P alloy layer, and a gold upper layer, where the Pd-P alloy layer prevents nickel corrosion and palladium diffusion, ensuring excellent wire bondability by controlling the phosphorus content and layer thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ni plating layer is used as a barrier layer to protect the primer layer from solder, then the primer layer is protected from corrosion, but the Ni plating layer corrodes during substitution gold plating, forming pinholes that deteriorate wire bondability
Solution Approach 1:
An intermediate layer based on a Pd-P alloy is introduced between the Ni-based lower layer and the Au-based upper layer. This intermediate layer acts as a mediator that prevents direct contact between the Ni layer and the substitution gold plating solution, thereby preventing Ni corrosion and pinhole formation while allowing the Au layer to maintain excellent wire bondability.
2Reliability
If a thick reduced gold plating layer (0.2-0.7 μm) is formed to close pinholes, then wire bondability is improved, but manufacturing cost increases significantly
Solution Approach 1:
The Pd-P alloy intermediate layer eliminates the need for thick reduced gold plating by preventing pinhole formation at the source. This allows the use of a thin Au layer (0.05-0.2 μm) that provides excellent wire bondability without the high cost associated with thick gold plating.
3Ease of manufacture
If only a thin substituted gold plating layer (0.1 μm or less) is formed to reduce cost, then manufacturing cost decreases, but the layer has many pinholes and poor bonding reliability
Solution Approach 1:
The Pd-P alloy intermediate layer provides a dense, pinhole-free barrier that enables the use of a thin Au layer (0.05-0.2 μm) while maintaining high bonding reliability. The intermediate layer compensates for the thinness of the Au layer by providing the necessary protective and bonding functions.
4Stability of the object's composition
If a Pd layer is formed between Ni and Au to prevent Ni diffusion, then Ni diffusion is suppressed, but Pd diffuses to the Au layer during soldering, deteriorating wire bondability
Solution Approach 1:
Phosphorus is added to the Pd layer to form a Pd-P alloy with specific composition (3-12 mass% P). This compositional change fundamentally alters the diffusion behavior during soldering, preventing Pd from diffusing to the Au layer while maintaining Ni diffusion barrier functionality. The P content is carefully controlled to achieve this balance.
5Productivity
If high-density wire bonding is performed with gold wires of 100 μm or less thickness, then mounting density is improved, but wire bondability deteriorates due to Ni corrosion and Pd diffusion
Solution Approach 1:
The Pd-P alloy intermediate layer provides a stable, pinhole-free barrier that ensures excellent wire bondability for high-density mounting applications. It prevents both Ni corrosion and Pd diffusion, creating an ideal surface for ultrasonic wire bonding of fine gold wires (100 μm or less thickness).
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 configuration enhances the bonding strength and reliability of the ceramic substrate parts by suppressing nickel corrosion and palladium diffusion, resulting in improved wire bondability and solder wettability, even under high-temperature conditions.
Implementation Method 1
an intermediate layer based on a Pd-P alloy between a Ni-based lower layer and an Au-based upper layer
Implementation Method 2
the diffusion of Pd to an uppermost Au layer is suppressed
Implementation Method 3
the nickel plating layer acts as a barrier layer for protecting the primer layer from a solder
Implementation Method 4
the strength of bonding between gold wires and a gold plating layer, which is achieved by mutual diffusion with ultrasonic vibration
Implementation Method 5
gold wires as thick as 100 μm or less are connected to the wire-bonding electrodes of a heated ceramic substrate part with ultrasonic vibration
Implementation Method 6
Pd is thermally diffused to the Au layer while soldering devices such as inductors, etc. to mounting electrodes before the wire bonding of semiconductor devices
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
A ceramic substrate part comprising on its upper surface pluralities of external electrodes comprising wire-bonding electrodes, each of which comprises a primer layer based on Ag or Cu, a Ni-based lower layer, an intermediate layer based on a Pd-P alloy containing 0.4-5% by mass of P, and a Au-based upper layer formed in this order on a ceramic substrate, the upper layer containing Pd after heated by soldering, and having a Au concentration of 80 atomic % or more based on the total concentration (100 atomic %) ofAu and Pd.