Wettable Flank Leadless Packages for Detectable Solder Joints
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Solution Overview
Problem
Current leadless semiconductor packages do not consistently form solder fillets that extend outward from the package, making it difficult for automated optical inspection systems to detect proper electrical connections, which is a challenge for high reliability applications.
Innovation Solution
The leadless semiconductor packages feature conductive plating on the leads, known as wettable flanks, that cover the lower and side surfaces of the leads, providing 100% coverage and a thickness greater than 7 micrometers to ensure consistent solder fillet formation and prevent oxidation, allowing solder joints to be easily detected by inspection systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If leadless packages use exposed leads on side surfaces for mounting, then the package footprint is reduced, but solder joints are not easily detected by AOI systems
Solution Approach 1:
The patent applies local quality by adding conductive plating specifically to the flanks (side surfaces) and lower surfaces of the leads, rather than uniformly plating the entire lead structure. This localized plating creates wettable surfaces that promote solder fillet formation and extend outward from the package, making solder joints detectable by AOI systems while maintaining the compact footprint of the leadless package structure.
2Reliability
If conductive plating is applied to lead surfaces, then solder fillet formation is improved, but manufacturing complexity increases
Solution Approach 1:
The patent implements preliminary action by applying conductive plating to the lead flanks and lower surfaces before the final package encapsulation and singulation steps. This advance plating ensures that the wettable surfaces are prepared in advance, allowing consistent solder fillet formation during subsequent mounting operations without requiring additional complex manufacturing steps after package completion.
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 conductive plating on the leads ensures that solder fillets consistently extend outward from the package, enabling easy detection by automated optical inspection systems and making the packages suitable for high reliability applications.
Implementation Method 1
The conductive plating improves the formation of solder fillets by substantially covering the lower and side surfaces of the leads to prevent oxidation
Implementation Method 2
The conductive plating on the leads encourages the formation of solder. Namely, when the leadless semiconductor package is mounted to a substrate, solder formed on the conductive plating consistently extend outward from the leadless semiconductor package to form solder fillets
Data Source
AI summary
The present disclosure is directed to leadless semiconductor packages with improved wettable flanks that encourage the formation of solder fillets when the leadless semiconductor package is mounted to a substrate. The solder fillets are consistently formed and are easily detectable by inspection systems, such as automated optical inspection (AOI) systems.