Surface-Contact Wire Extensions for Inspectable QFN Solder Joints
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Solution Overview
Problem
QFN/SON devices face challenges in high reliability environments due to solder fatigue, thermo-mechanical strains, moisture absorption, and inadequate automated solder joint inspection, which hinder their adoption in industries like automotive, medical, and aviation.
Innovation Solution
Modifying non-leaded packages with wires extending from the surface contacts to facilitate inspectable solder joints and increase standoff height, reducing solder fatigue issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If QFN/SON devices use non-leaded surface contacts inset into the mold cap, then device size is reduced to chip-scale, but automated solder joint inspection becomes inadequate
Solution Approach 1:
The patent extends surface contacts vertically from the bottom surface of the mold cap, adding a height dimension to otherwise planar contacts. This dimensional change allows inspection equipment to access and image solder joints from the bottom side, resolving the inspection difficulty while preserving the compact chip-scale footprint of the device.
Solution Approach 2:
The extended surface contacts act as intermediaries that bridge the solder joint between the device and PCB. By protruding from the mold cap, these contacts provide a visible interface that allows inspection equipment to detect solder joint quality without requiring direct access to the buried joint interface.
2Length of stationary object
If QFN/SON devices have lower standoff height, then device profile is reduced, but thermo-mechanical strains increase due to CTE mismatch
Solution Approach 1:
The patent modifies the standoff height parameter by extending surface contacts beyond the mold cap surface. This parameter change increases the distance between the device body and PCB, reducing the leverage effect of CTE mismatch during thermal cycling and thereby decreasing thermo-mechanical strains on the solder joints.
3Difficulty of detecting and measuring
If surface contacts are extended with wires, then solder joint inspection capability is improved, but device complexity increases
Solution Approach 1:
The extended surface contacts serve multiple functions: they maintain electrical connectivity, provide mechanical support, enable solder joint attachment to PCB, and facilitate automated inspection. This multi-functionality reduces the need for separate inspection features, offsetting the added complexity with functional consolidation.
Data Source
AI summary
An electronic package includes an electronic component including terminals, a plurality of surface contacts, at least some of the surface contacts being electrically coupled to the terminals within the electronic package, a mold compound covering the electronic component and partially covering the surface contacts with a bottom surface exposed from the mold compound, and a plurality of wires extending from exposed surfaces of the surface contacts, each of the wires providing a solderable surface for mounting the electronic package at a standoff on an external board.