Semiconductor Package Substrate With Wettable Side Flanks
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Solution Overview
Problem
Current semiconductor packages with non-wettable lead flanks hinder automated optical inspection and reduce solder strength, making it difficult to inspect solder joints, especially in applications requiring visibility under low power microscopy, such as medical, military, and automotive industries.
Innovation Solution
A semiconductor package substrate with side wettable flanks (SWFs) is developed, featuring a non-metallic material with exposed terminals on the side surfaces, including a vertical groove or U-shape slot hole, allowing for improved solderability and enabling 100% automatic optical inspection post-assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional lead frame packages are used with non-wettable flanks, then the package structure is simple and manufacturing is easier, but automated optical inspection of solder joints becomes difficult and solder strength is reduced
Solution Approach 1:
The patent applies local quality by creating wettable flanks only at specific locations where solder joints need to be inspected, rather than making the entire lead frame wettable. The wettable flank is formed by removing the non-wettable coating from the flank surface, exposing the underlying metal to enable solder wicking, while maintaining the non-wettable coating elsewhere for protection and simplicity.
2Measurement precision
If pullback lead terminals are used, then the package structure is simpler, but solder joint visibility for inspection is reduced
Solution Approach 1:
The patent inverts the traditional approach by extending the lead terminal beyond the package body (no pullback design) and creating a wettable flank that allows solder to climb up the side surface. This inversion makes the solder joint visible from the side for automated optical inspection, rather than hiding it within the package as in traditional pullback designs.
3Strength
If non-wettable lead flanks are used, then manufacturing is easier and protection is better, but solderable area is reduced and solder strength decreases
Solution Approach 1:
The patent applies local quality by creating wettable flanks only at specific locations where solder joints need to be inspected, rather than making the entire lead frame wettable. The wettable flank is formed by removing the non-wettable coating from the flank surface, exposing the underlying metal to enable solder wicking, while maintaining the non-wettable coating elsewhere for protection and simplicity.
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 SWF design enhances board-level mechanical robustness and allows for precise, automatic visual inspection of solder joints, ensuring reliable connections and meeting the requirements of high-speed data communication applications like automotive Ethernet.
Implementation Method 1
This assembly is encapsulated with a mould compound, which protects the die and wire bonds from environmental and physical damage.
Implementation Method 2
the surface of the exposed lead or flank is flush with the mould compound of the device such that solder does not readily climb-up or 'wick' the flank of the package
Data Source
Figure 1
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AI summary
The disclosure proposes a semiconductor package substrate (1) made from non-metallic material having a first (top) surface (6), a second (bottom) surface (7) opposite from the first surface, and at least one side surface (8), the substrate comprising at least two pads (2) positioned on the first surface (6) and suitable for receiving an electronic element (3), an encapsulant material layer (4) covering the first surface (6), at least two terminals (5) positioned on the second surface and electrically connected to the pads (2), wherein a portion of at least one of the two terminals (5) is exposed at the at least one side surface (8) and structured as a wettable flank (9).