Leadless Semiconductor Package Recesses for PCB Solder Joint Reliability
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Solution Overview
Problem
Leadless packaged semiconductor devices, such as QFN devices, face challenges in reliably connecting to printed circuit boards due to the vulnerability of solder joints, which can easily become void, fail, or crack.
Innovation Solution
A packaged semiconductor device design featuring electrically conductive contacts with recesses and a molding compound, along with a manufacturing method using lead-frames and connection bars, where the molding compound is disposed and the connection bar is separated to create recesses between the contacts, enhancing the mechanical and electrical connection with the PCB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If leadless packaged semiconductor devices are used to reduce size, then device compactness is improved, but solder joint reliability deteriorates
Solution Approach 1:
The device is segmented into distinct functional regions: a central active region containing the device die, and peripheral contact regions with electrically conductive contacts arranged around it. This segmentation allows the compact central region to maintain small size while the distributed peripheral contacts provide multiple reliable solder joint locations, resolving the contradiction between compactness and solder joint reliability.
Solution Approach 2:
The electrically conductive contacts are arranged in a two-dimensional peripheral pattern around the central device die, transitioning from a traditional linear lead arrangement to a distributed circular pattern. This dimensional reorganization maximizes the use of available package perimeter space, providing multiple solder joint opportunities within a compact footprint, thus improving reliability without increasing device volume.
2Reliability
If electrically conductive contacts are arranged around the peripheral region, then connection reliability is improved, but device complexity increases
Solution Approach 1:
The molding compound performs multiple functions simultaneously: it provides mechanical support for the device die, electrically isolates the electrically conductive contacts from each other, and creates the recesses that define the contact arrangement. By merging these functions into a single material and manufacturing step, the design achieves improved connection reliability without proportionally increasing device complexity.
Solution Approach 2:
The recesses formed by the molding compound serve multiple purposes: they provide mechanical clearance between adjacent electrically conductive contacts, define the spatial arrangement of contacts, and facilitate solder application during assembly. This multi-functionality reduces the need for additional structural elements, maintaining manufacturing simplicity while achieving reliable connections.
3Reliability
If recesses are created between electrically conductive contacts, then solder joint integrity is improved, but manufacturing complexity increases
Solution Approach 1:
The recesses between electrically conductive contacts are pre-formed during the molding compound fabrication process, before the actual soldering operation. This preliminary creation of clearance spaces ensures proper solder flow and joint formation without requiring additional post-molding processing steps, thereby improving solder joint integrity while avoiding significant increases in manufacturing complexity.
Solution Approach 2:
The molding compound automatically forms the recesses through its own curing and shrinkage characteristics during the standard molding process. The material's natural behavior creates the necessary clearance spaces between contacts without requiring separate machining, etching, or forming operations, thus improving solder joint integrity while maintaining manufacturing simplicity.
Data Source
AI summary
A packaged semiconductor device has a first surface, a second surface opposite the first surface, and sidewalls therebetween. The semiconductor device includes: a device die arranged in a central region surrounded by the sidewalls; a plurality of electrically conductive contacts around a peripheral region of the second surface; and molding compound between electrically conductive contacts, and between the device die and the electrically conductive contacts. The electrically conductive contacts each have an end side surface forming a part of the sidewall, and remainder of the sidewall comprises surfaces of the molding compound. The packaged semiconductor device has recesses between the electrically conductive contacts, each recess has a first distance along the sidewall from the second surface towards the first surface, and a second distance from the sidewall towards the central region.