Leadless Semiconductor Packages With Wettable Flanks
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Solution Overview
Problem
Leadless semiconductor packages with plated leadframes face challenges in forming visible filleted solder connections due to the lack of wettable flanks, making visual inspection difficult and requiring alternative verification methods.
Innovation Solution
The method involves forming leadless packages using a sacrificial substrate with conductive layers and contacts that extend across saw streets, allowing for the exposure of wettable flanks during singulation, enabling the formation of filleted solder connections when mounted on a PCB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a plated leadframe is used to reduce package height, then package height is reduced, but wettable flanks are lost making visual inspection difficult
Solution Approach 1:
The leadframe structure is segmented into multiple functional zones: solderable flanks that extend to the side surfaces of the package for visual inspection, and non-solderable flanks that are enclosed by encapsulant for structural support. This segmentation allows the package to simultaneously achieve low height while maintaining visible solder joints for inspection.
Solution Approach 2:
Different portions of the leadframe are given different properties: the flanks near the package edges are made solderable and exposed to enable visual inspection, while other portions are made non-solderable and enclosed by encapsulant to provide structural support. This local differentiation resolves the contradiction between height reduction and inspectability.
2Strength
If leadframe flanks are enclosed by encapsulant to provide structural support, then structural support is improved, but visual inspection of solder connections becomes impossible
Solution Approach 1:
The encapsulant is segmented to selectively enclose only the non-solderable flanks while leaving the solderable flanks exposed at the package side surfaces. This allows structural support to be maintained for enclosed portions while visual inspection remains possible for the exposed solderable portions.
Solution Approach 2:
The encapsulant provides structural support at specific locations where flanks are enclosed, while deliberately leaving other locations (side surfaces) open to expose solderable flanks for visual inspection. This localized application of encapsulant resolves the contradiction between structural support and inspectability.
3Ease of manufacture
If conventional leadless packages are used without wettable flanks, then manufacturing is simpler, but solder connection verification requires additional inspection technologies
Solution Approach 1:
The leadframe structure itself provides the visual inspection capability through its exposed solderable flanks, eliminating the need for external inspection technologies. The package structure serves its own inspection function, maintaining manufacturing simplicity while reducing inspection complexity.
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 allows for visually verifiable solder connections while maintaining a thin package height, ensuring proper interconnection and reducing the need for additional inspection technologies.
Implementation Method 1
Leadless package 122 includes a plated leadframe 104 formed on a sacrificial substrate 100
Implementation Method 2
An encapsulant or molding compound 40 is disposed around semiconductor die 24 and leadframe 26 for electrical isolation and protection from contaminants
Implementation Method 3
Solder 50 is reflowed between leadframe contacts 26a and contact pads 22 on PCB 20 to form a metallurgical and electrical connection
Data Source
AI summary
A leadless package with wettable flanks is formed by providing a substrate and plating a metal layer onto the substrate to form a contact on the substrate extending across a saw street. An encapsulant is deposited over the contact. The substrate is removed to expose the contact and encapsulant. The encapsulant and contact are singulated. In some embodiments, the substrate includes a ridge, and the contact is formed over the ridge.