Flip-Chip Solder Precoat for BGA Impact Resistance
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Solution Overview
Problem
In semiconductor devices with flip-chip connections, electroless Ni-Au plating is prone to poor impact resistance due to phosphorus mixing and micro voids, leading to weakened joint interfaces between solder balls and wiring substrates, which compromises the reliability and signal quality of the connection.
Innovation Solution
A solder precoat is formed on the wiring substrate's lands using a Sn-Cu based lead-free solder, eliminating the need for electroless plating and reducing the risk of micro voids, thereby enhancing the impact resistance and reliability of the joint interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electroless Ni-Au plating is used on the wiring substrate surface, then the wiring design freedom is increased and signal quality is improved by eliminating the plating lead, but the impact resistance of the joint part deteriorates due to phosphorus mixing and micro void formation
Solution Approach 1:
The invention extracts and removes the harmful element (electroless Ni-Au plating layer containing phosphorus) that causes micro voids and poor impact resistance. By eliminating this intermediate plating layer, the patent directly connects the copper land to the solder ball, thereby removing the source of the problem while preserving the wiring design freedom advantage of electroless plating.
Solution Approach 2:
The patent discards the conventional electroless Ni-Au plating process and recovers the underlying copper land surface for direct soldering. This approach abandons the problematic plating layer that creates phosphorus concentration and micro voids, while recovering the copper surface to form a stronger, more reliable joint with the solder ball.
2Ease of operation
If electroless Ni-Au plating is applied to the land surface, then the plating lead can be obviated and wiring design freedom increased, but the joint interface between land and solder ball becomes vulnerable and impact resistance deteriorates
Solution Approach 1:
The invention extracts and eliminates the electroless Ni-Au plating layer from the land surface, removing the source of phosphorus mixing and micro void formation. This extraction preserves the wiring design flexibility advantage while eliminating the reliability problem at the joint interface.
Solution Approach 2:
The patent creates a composite structure by directly bonding solder material to the copper land surface without an intermediate Ni-Au plating layer. This direct metal-to-metal bonding creates a more reliable joint interface compared to the composite structure of copper-Ni-Au-solder that inherently contains phosphorus and micro voids.
3Ease of manufacture
If P is mixed in electroless Ni-Au plating, then the plating process can be completed, but micro voids are generated in the P-concentrated layer and impact resistance deteriorates
Solution Approach 1:
The invention extracts and removes the entire electroless Ni-Au plating process from the manufacturing flow, thereby eliminating the phosphorus mixing issue and micro void formation. By taking out this problematic process step, the patent achieves both ease of manufacture (through simplified process) and high manufacturing precision (through elimination of defects).
Solution Approach 2:
The patent replaces the complex electroless Ni-Au plating process with a simpler, more direct soldering approach. This substitution uses a cheaper, more reliable method that eliminates the need for phosphorus-containing plating chemicals and the complex plating process steps, thereby improving both manufacturability and product quality.
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 use of a Sn-Cu based solder precoat improves the impact resistance and reliability of the joint between the solder balls and the wiring substrate, stabilizing the semiconductor device's quality and preventing signal quality deterioration.
Implementation Method 1
applying solder paste to a plurality of lands on the side of the undersurface of the wiring substrate; after the (a) step, melting the solder paste or the solder ball on the side of the top surface and the solder paste on the side of the undersurface by reflow to form solder precoat on each of the surfaces of the lands
Data Source
AI summary
To aim at improvement of reliability of a semiconductor device of flip chip connection type. In assembling a BGA of flip chip connection type, when a semiconductor chip is solder-connected by a flip chip connection, because solder precoat is formed on the surface of a land on the side of an undersurface of a wiring substrate, the connection between the land and a solder ball, which is an external terminal, is solder-connection, and therefore, it is possible to increase impact resistance of a connection part between the land and the solder ball and to aim at improvement of reliability of the BGA.