Leadframe Recess Filler Structure for Stronger PCB Solder Joints
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Solution Overview
Problem
The reliability of leadless packages is compromised due to weakened solder joints caused by differing coefficients of thermal expansion between the package and the printed circuit board, and as packages shrink, available space for solder joints is limited, necessitating strong solder bonds.
Innovation Solution
The introduction of recesses on the outer surface of the leads filled with a filler material, such as solder, provides a wetable surface for improved adhesion during mounting and enhances visual inspection of solder joints, ensuring stronger connections between the package and the PCB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If packages are reduced in size to achieve smaller package dimensions, then package size is improved, but the available space for solder joints is reduced and solder joint strength deteriorates
Solution Approach 1:
The patent applies local quality by creating recesses specifically at the solder joint locations on the lead surfaces. These recesses concentrate the filler material where it is most needed for strengthening solder joints, rather than uniformly distributing material throughout the entire package. This allows the package to maintain small overall dimensions while having enhanced solder joint strength at critical locations.
Solution Approach 2:
The patent applies preliminary action by pre-filling the recesses with filler material during the leadframe manufacturing process, before the actual soldering operation. This preliminary placement of filler material ensures that when the package is mounted, the solder has immediate adhesion points and proper wetting surfaces are already prepared, compensating for the limited space available in miniaturized packages.
2Length of moving object
If different coefficients of thermal expansion between package and PCB are present, then package miniaturization is enabled, but solder joint reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-preparing the lead surfaces with recesses filled with filler material that has compatible thermal expansion properties. This preliminary preparation creates a transition structure that can better accommodate thermal cycling stresses, improving solder joint reliability in miniaturized packages subject to CTE mismatch.
Solution Approach 2:
The patent applies composite materials by using a filler material in the recesses that is specifically selected to bridge the thermal expansion difference between the package substrate and the PCB. This filler material acts as a composite interface layer that reduces thermal stress transmission to the solder joints, thereby improving reliability despite CTE mismatch.
3Ease of manufacture
If traditional flat lead surfaces are used, then manufacturing simplicity is maintained, but visual inspection of solder joints becomes difficult
Solution Approach 1:
The patent applies local quality by modifying only the surface topology at specific locations (the recesses) while keeping the overall leadframe structure and manufacturing process simple. The recesses create localized features that enhance solder material accumulation and provide visual indicators of proper solder joint formation, without requiring complex manufacturing changes.
Solution Approach 2:
The patent applies the principle of visual indication by creating surface features (recesses) that cause observable changes in the appearance of solder joints. The recesses allow solder material to pool and create visible menisci or surface tension indicators that make it easier to inspect whether proper soldering has occurred, similar to how color changes indicate process 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
This approach strengthens solder joints, improves adhesion, and facilitates easier visual inspection, addressing the limitations of existing technologies by providing a robust and reliable connection between the package and the PCB.
Implementation Method 1
The filler material in the recesses provides a wetable surface for filler material, such as solder, to adhere to during mounting of the package to another device
Data Source
AI summary
Embodiments of the present disclosure are directed to a leadframe package with recesses formed in outer surface of the leads. The recesses are filled with a filler material, such as solder. The filler material in the recesses provides a wetable surface for filler material, such as solder, to adhere to during mounting of the package to another device, such as a printed circuit board (PCB). This enables strong solder joints between the leads of the package and the PCB. It also enables improved visual inspection of the solder joints after the package has been mounted.