QFN Package Substrate Connection Frame for Plated Cut Electrodes
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Solution Overview
Problem
Copper electrodes in QFN packaged chips are prone to oxidation, leading to degraded solder wetting characteristics, making it difficult to fix the chips to a wiring board, and the cutting process is challenging due to thickness variations and potential blade clogging and burr formation.
Innovation Solution
A package substrate design with a metallic lead frame and connection frame, where the connection frame is superposed on the lead frame, allowing for a cut groove forming step followed by electroplating to form a plating layer on exposed cut surfaces, and subsequent division into individual chips with precise cutting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrodes are half cut by a predetermined depth to enable plating processing, then the solder wetting characteristics are improved, but it is difficult to form grooves of high-accuracy cutting depth due to package substrate thickness variation and warp
Solution Approach 1:
The patent introduces a connection frame as an intermediary component between the lead frame and the mold resin. This connection frame serves as a mediator that enables plating processing to be performed on its side surfaces after cutting, rather than directly on the electrodes of the lead frame. The connection frame acts as a buffer that decouples the cutting process from the plating process, allowing plating to be applied to the connection frame's side surfaces which are more accessible and easier to control for plating deposition.
Solution Approach 2:
The patent segments the frame structure into three distinct parts: the lead frame, the connection frame, and the mold resin. This segmentation allows the connection frame to be treated as a separate component that can be independently processed. The connection frame's side surfaces are specifically designed to be exposed after cutting, enabling plating processing to be performed on these surfaces rather than on the electrodes themselves, thus resolving the contradiction between achieving good solder wetting and maintaining cutting depth accuracy.
2Strength
If the electrodes are half cut to expose side surfaces for plating, then the mechanical strength of solder joint parts is enhanced, but clogging of the cutting blade and burr formation on the electrodes occur
Solution Approach 1:
The connection frame serves as an intermediary that absorbs the cutting process challenges. Instead of cutting directly through the electrodes to expose their side surfaces, the cutting process cuts through the connection frame, which is more tolerant to cutting variations. The plating is then applied to the connection frame's side surfaces, which are easier to process without causing blade clogging or burr formation on the actual electrodes.
Solution Approach 2:
The patent applies plating processing locally to the side surfaces of the connection frame rather than to the entire electrode structure. This localized approach allows plating to be applied only where needed for solder joint strength, while avoiding the problems associated with cutting and plating the electrodes themselves. The connection frame's side surfaces are specifically designed to be the location for plating, separating the plating function from the electrode function.
3Reliability
If plating processing is applied to the electrodes after half cutting, then the solder wetting characteristics are maintained, but the process complexity increases due to multiple cutting and plating steps
Solution Approach 1:
The patent merges the plating function with the connection frame rather than requiring separate plating of each electrode. By applying plating to the side surfaces of the connection frame as a unified structure, the process simplifies the overall manufacturing sequence. The connection frame acts as a carrier that consolidates the plating operation, reducing the complexity compared to individually plating multiple electrodes after cutting.
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 approach relaxes the accuracy requirements for cutting depth, prevents blade clogging, and maintains solder wettability, enhancing the mechanical strength of solder joints.
Implementation Method 1
the connection frame forms an electrode when electroplating processing is applied to sections of the first electrode portions
Data Source
AI summary
A package substrate includes a metallic lead frame that includes first frame portions in a lattice shape along planned dividing lines and a plurality of first electrode portions extending from each of the first frame portions, a connection frame that includes second frame portions in a lattice shape along the planned dividing lines and a plurality of second electrode portions extending from each of the second frame portions, the connection frame being superposed on a side of the lead frame on which a device chip is disposed, and a mold resin that covers the device chip and the connection frame. Distal ends of the second electrode portions are formed in a protruding shape and connected to the first electrode portions, and the connection frame forms an electrode when electroplating processing is applied to sections of the first electrode portions.