Semiconductor Package Pads With Enlarged Ends for PCB Anchorage
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Solution Overview
Problem
Semiconductor devices with QFN or LGA packages face challenges in solder joint reliability and anchorage to printed circuit boards due to variability in welding strength and thermal expansion coefficients, which current wettable flanks only partially address.
Innovation Solution
The semiconductor device design includes electrically conductive pads with enlarged end portions extending over the package molding material, formed through galvanic plating or other metal deposition techniques, to increase the soldering surface area and mechanical coupling, thereby enhancing solder joint reliability and anchorage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional QFN or LGA packages with standard pads are used, then the device structure is simple and manufacturing is easy, but the solder joint reliability and anchorage strength are insufficient due to variability in welding strength and thermal expansion coefficients
Solution Approach 1:
The patent extends the conductive pads in the vertical dimension by forming enlarged end portions that protrude from the package molding material rear surface. This dimensional extension increases the soldering surface area and creates overlapping solder joints, thereby improving solder joint reliability and anchorage strength without fundamentally changing the horizontal package structure
Solution Approach 2:
The conductive pads are pre-formed with enlarged end portions before final package assembly. This preliminary formation of extended pads allows for better solder distribution and stronger mechanical coupling to be established in advance, improving solder joint reliability before the device is mounted on the PCB
2Reliability
If wettable flanks are used to increase solder attachment area, then solder adhesion is slightly improved and optical inspection is facilitated, but the overall welding strength and solder joint reliability remain insufficient
Solution Approach 1:
Instead of only increasing solder attachment area laterally through wettable flanks, the patent extends the pads vertically by forming enlarged end portions that protrude from the package molding material. This vertical extension creates overlapping solder joints that significantly enhance welding strength and solder joint reliability beyond what wettable flanks alone can achieve
3Strength
If the soldering surface area is increased to improve anchorage strength, then the mechanical coupling to PCB is enhanced, but the package structure becomes more complex and manufacturing becomes more difficult
Solution Approach 1:
The patent increases soldering surface area by extending pads in the vertical dimension through enlarged end portions that protrude from the package molding material rear surface. This approach achieves enhanced anchorage strength and mechanical coupling without requiring significant increases in horizontal pad dimensions or overall package footprint
Solution Approach 2:
The enlarged end portions are formed selectively at specific locations where enhanced anchorage is needed, rather than uniformly increasing the size of all pads. This localized enhancement of pad structure provides improved mechanical coupling at critical interfaces while maintaining simplicity in other areas of the package structure
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 solution improves solder joint reliability and strengthens the anchorage of semiconductor devices to printed circuit boards, offering better thermal management and longer lifespan compared to previous methods.
Implementation Method 1
formed through galvanic plating or other metal deposition techniques
Data Source
AI summary
A semiconductor device comprises at least one semiconductor die electrically coupled to a set of electrically conductive leads, and package molding material molded over the at least one semiconductor die and the electrically conductive leads. At least a portion of the electrically conductive leads is exposed at a rear surface of the package molding material to provide electrically conductive pads. The electrically conductive pads comprise enlarged end portions extending at least partially over the package molding material and configured for coupling to a printed circuit board.