Leadframe Terminal Plating for Burr-Free Surface-Mount IC Packages
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Solution Overview
Problem
Existing methods for forming surface-mount IC packages with solder-enhancing leadframe terminals often result in burrs and incomplete removal of mold compound, leading to electrical shorting and reduced solder wettability.
Innovation Solution
A process involving laser grooving to remove mold compound, followed by a saw step cut to further clear the leadframe terminal grooves, and subsequent plating with solder-enhancing material to improve solder connections between leadframe terminals and PCBs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques are used to form plated leadframe terminals, then leadframe terminals can be plated with solder-enhancing material, but burrs from leadframe material may cause electrical shorting between adjacent leadframe terminals
Solution Approach 1:
The patent applies preliminary action by performing laser grooving and chemical deflash processes before the sawing and plating steps. The laser grooving removes mold compound from the leadframe terminal groove, and chemical deflash further cleans the surfaces, ensuring that no mold compound or burrs are present before plating. This preliminary preparation prevents burr formation and ensures clean surfaces for solder-enhancing plating, thereby improving electrical connection reliability.
2Reliability
If conventional techniques are used to form plated leadframe terminals, then leadframe terminals can be plated with solder-enhancing material, but mold compound may remain on leadframe terminal surfaces reducing solder wettability
Solution Approach 1:
The patent replaces conventional mechanical cleaning methods with laser grooving technology. The laser beam precisely removes mold compound from the leadframe terminal groove and adjacent surfaces through ablation, achieving complete removal without mechanical contact that could leave residues. This substitution ensures thorough mold compound removal and creates clean surfaces for optimal solder-enhancing plating adhesion and solder wettability.
Solution Approach 2:
The patent employs chemical deflash as a secondary process after laser grooving to further remove any remaining mold compound residues. The chemical solution chemically etches and removes organic material from the leadframe surfaces, ensuring complete cleanliness before plating. This parameter change from physical to chemical removal enhances the completeness of mold compound removal and improves solder connection reliability.
3Ease of manufacture
If a single cutting process is used for singulation, then manufacturing complexity is reduced, but burr formation and incomplete mold compound removal occur
Solution Approach 1:
The patent segments the singulation process into multiple distinct steps: laser grooving to remove mold compound, chemical deflash to clean surfaces, sawing to cut through the leadframe, and plating to apply solder-enhancing material. Each step is optimized for its specific function, with laser grooving handling mold compound removal, chemical deflash handling surface cleaning, and sawing handling the actual cut. This segmentation ensures high terminal surface quality and complete mold compound removal while maintaining manufacturing efficiency through automated integration of all steps.
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 process enhances solder connections by reducing burr formation and ensuring effective removal of mold compound, thereby improving the solder-enhancing plating and overall reliability of the IC packages.
Implementation Method 1
A laser grooving process may be performed to remove at least a portion of mold compound from a leadframe terminal groove
Implementation Method 2
Exposed leadframe surfaces, including terminal end surfaces exposed by the saw step cut, are plated with a solder-enhancing material, e.g., tin
Data Source
AI summary
Flat no-leads integrated circuit (IC) packages are formed with solder wettable leadframe terminals. Dies are mounted on die attach pads, bonded to adjacent leadframe terminal structures, and encapsulated in a mold compound. A laser grooving process removes mold compound from a leadframe terminal groove extending along a row of leadframe terminal structures. A saw step cut along the leadframe terminal groove extends partially through the leadframe thickness to define a saw step cut groove. Exposed leadframe surfaces, including surfaces exposed by the saw step cut, are plated with a solder-enhancing material. A singulation cut is performed along the saw step cut groove to define leadframe terminals with end surfaces plated with the solder-enhancing material. The laser grooving process may improve the results of the saw step cut, and the saw step cut may remove mold compound not removed by the laser grooving process.