Wettable Lead Flanks for QFN Solder Joint Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Quad Flat No-Lead (QFN) and Power Quad Flat No-Lead (PQFN) packaging approaches impair solder joint strength and reliability due to mold compound filling recessed leads, reducing the solderable area and visibility of solder fillets.
Innovation Solution
A method involving a selectively plated lead frame with exposed copper areas, partial etching to form recesses, and re-plating to create wettable lead flanks, allowing for increased solderable area and improved inspection of solder fillets after singulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If injection molding is performed after mounting the integrated circuit die on the lead frame with selectively recessed leads, then the package structure is formed, but the mold compound material fills the recesses, impairing visibility of solder fillets and reducing solderable area
Solution Approach 1:
The patent applies preliminary plating to the lead frame leads before the injection molding process. A solderable material is deposited on the leads in advance, creating a protective and functional coating that prevents the mold compound from contaminating the solderable surfaces. This preliminary action ensures that the leads remain wettable and visible for subsequent soldering operations, resolving the contradiction between forming the package structure and maintaining solder joint reliability
Solution Approach 2:
The patent implements preliminary anti-action by applying a protective plating layer to the leads before molding. This anti-action prevents the harmful effect of mold compound contamination on the solderable surfaces. The plating creates a barrier that actively counteracts the potential filling and obscuring effects of the mold compound, ensuring that the leads remain visible and solderable after the molding process
2Shape
If the lead frame leads are recessed before molding, then the package structure is defined, but the mold compound fills the recesses, reducing the available solderable area
Solution Approach 1:
The patent applies preliminary plating to the recessed leads before the injection molding process. By depositing solderable material on the leads in advance, the patent ensures that even though the leads are recessed to define the package structure, the solderable surface area is preserved and enhanced. The plating material fills the recesses with a functional coating that maintains solderability while allowing the mold compound to form the desired package shape
3Ease of manufacture
If the mold compound fills the recessed leads, then the package encapsulation is complete, but the visibility of solder fillets is reduced
Solution Approach 1:
The patent applies preliminary plating to the leads before molding, creating a distinct solderable surface that contrasts with the mold compound. This preliminary coating ensures that after encapsulation, the solder fillets formed on the plated leads remain visible and detectable, as the plating material provides a recognizable surface特征 for inspection purposes
Solution Approach 2:
The patent utilizes color or appearance changes through the plating process. The plated leads have a distinct appearance compared to the mold compound, which enhances the visibility of solder fillets during inspection. The plating material's optical properties create a visual contrast that makes it easier to detect and measure solder fillet quality after the package is encapsulated
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
Enhances solder joint strength and reliability while maintaining efficient sawn lead frame packaging processes, allowing for visual inspection of solder fillets post-soldering.
Implementation Method 1
a lead frame packaging process is provided wherein a selectively plated lead frame is provided; an integrated circuit die is mounted to the selectively plated lead frame
Implementation Method 2
a partial etch process is applied to form recesses in the lead frame
Implementation Method 3
the recessed areas are then re-plated to form wettable lead flanks
Data Source
AI summary
A method and apparatus are described for fabricating a low-pin-count chip package (701) including a die pad (706) for receiving an integrated circuit device and a plurality of connection leads (702) having recessed lead ends (704) at the outer peripheral region of each contact lead. After forming the package body (202) over the integrated circuit device, unplated portions (104) of the exposed bottom surface of the selectively plated lead frame are partially etched to form recessed lead ends (302) at the outer peripheral region of each contact lead, and the recessed lead ends are subsequently re-plated (402) to provide wettable recessed lead ends at the outer peripheral region of each contact lead.