Coated Surface-Mount IC Package Sidewall Solder Connection
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Solution Overview
Problem
Conventional surface-mount integrated circuit (IC) packages, such as flat no-leads and flat leads packages, face challenges in forming effective and reliable solder bonds between leadframe terminals and printed circuit boards (PCBs) due to incomplete solder-enhancing coatings, resulting in inadequate physical and electrical connections.
Innovation Solution
The method involves forming IC packages with leadframe surfaces coated using a tin immersion process to cover the full height of the terminal sidewalls or distal ends, ensuring comprehensive solder-enhancing coverage for improved solder connections, which includes a combination of tin electroplating and immersion processes to ensure the solder material forms a fillet that covers at least 80% or 100% of the surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional partial coating methods are used on leadframe terminals, then manufacturing complexity is reduced, but solder connection reliability deteriorates due to incomplete coverage of terminal surfaces
Solution Approach 1:
The patent applies preliminary action by forming a complete coating on the leadframe terminal surfaces before the singulation cut is made. The coating process is performed on the full-height terminal structure while it is still attached to the leadframe, ensuring that the entire sidewall surface is covered before any cutting occurs. This preliminary coating ensures that when the terminal is later separated and soldered, the coating is already in place and cannot be compromised by subsequent handling or positioning operations.
Solution Approach 2:
The patent segments the manufacturing process into distinct stages: first forming the complete coating on the terminal sidewalls while attached to the leadframe, then performing the singulation cut to separate individual terminals, and finally proceeding to soldering. This segmentation allows the coating process to be performed on a stable, supported structure rather than on isolated terminals, ensuring complete and uniform coverage before the terminals are separated for final assembly.
2Reliability
If full-height coating is applied to terminal sidewalls, then solder material flow and wetting are improved, but manufacturing process complexity increases due to additional coating steps
Solution Approach 1:
The patent performs the full-height coating operation as a preliminary step before singulation, when the terminal structure is still supported by the leadframe. This timing allows the coating material to be applied uniformly to the entire sidewall surface area without requiring complex positioning or handling of individual terminals. The coating is established in advance, ensuring complete coverage before any subsequent manufacturing steps are performed.
Solution Approach 2:
The patent merges the coating operation with the period when terminals are still attached to the leadframe structure. By combining the coating step with this intermediate state in manufacturing, the process leverages the structural support of the leadframe to achieve complete sidewall coverage without requiring additional complex fixtures or handling mechanisms. The coating process is integrated into the existing manufacturing sequence rather than being added as a separate, isolated operation.
3Reliability
If coating is performed before singulation cut, then coating coverage is complete, but risk of coating damage during cutting increases
Solution Approach 1:
The patent applies beforehand cushioning by performing the coating operation before the singulation cut, when the terminal structure is still supported and protected by its attachment to the leadframe. This timing provides mechanical support to the coated surface during the coating process and immediately before cutting, reducing the risk of damage. The coating is established while the structure is most stable, and the subsequent cutting is performed with awareness of the fragile coated surface.
Solution Approach 2:
The patent performs the coating as a preliminary action before any cutting operations, ensuring that the coating is fully established and adhered to the terminal surface while the terminal is still supported by the leadframe. This preliminary coating creates a protective layer that can withstand subsequent handling and cutting operations, rather than attempting to apply coating after the terminal has been separated and is more vulnerable to damage.
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 enhances the flow and wetting of solder material, resulting in significantly improved solder connections that provide reliable physical and electrical bonds between the IC packages and the PCB, addressing the inefficiencies of partial coatings in existing methods.
Implementation Method 1
forming a coating of a coating material over the full height of the exposed terminal structure sidewall surface
Implementation Method 2
forming a first coating of a first coating material
Data Source
AI summary
Methods are disclosed for forming flat no-leads packages (e.g., QFN packages) with soldering surfaces that are fully coated, e.g., by a tin immersion process, for improved solder connections of the packages to a PCB or other structure. The method includes forming a flat no-leads package structure including a leadframe terminal structure having an exposed top or bottom surface; forming a first coating of a first coating material (e.g., tin) on the exposed top or bottom surface; cutting through a full thickness of the leadframe terminal structure to define an exposed terminal sidewall surface; and forming a second coating of a second coating material (e.g., tin) over the full height of the exposed terminal sidewall surface. The coating (e.g., tin immersion coating) covering the full height of the leadframe terminal sidewall may enhance the flow of solder material, e.g., when soldering to a PCB, to provide an improved solder connection.