QFN Packaging Structure with Wettable Flanks for Solder Coating
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Solution Overview
Problem
The traditional quad flat no leads (QFN) package structure has non-wettable flanks, making it difficult to coat solder and leading to oxidation, which complicates automated optical inspection due to protrusions formed during solder connection between the package and the printed circuit board.
Innovation Solution
A packaging process and structure with wettable flanks, achieved by embedding an electronic component, thermal conduction structure, and metal layers within an insulation structure, forming concaves and openings to facilitate solder coating and optical inspection, using a metal re-distribution layer to connect the components and enable easy coating of conducting material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the lead frame surface on the flank is not electroplated to maintain smaller volume and cheaper cost, then the package structure is simpler and more cost-effective, but the flank becomes difficult to coat with solder and oxidizes easily
Solution Approach 1:
The patent applies local quality by selectively electroplating only the flank surfaces of the lead frame that require solderability, while leaving other areas unplated to maintain cost-effectiveness. The insulating coating is applied locally at specific positions on the flank surfaces, creating different functional zones on the same component - plated areas for solder attachment and unplated areas for cost savings.
Solution Approach 2:
The patent introduces an insulating coating as an intermediary layer at specific positions on the electroplated flank surfaces. This intermediate insulating layer prevents solder from spreading to unwanted areas while maintaining the solderability of the plated surfaces, resolving the conflict between achieving good solder joints and preventing solder proliferation.
2Ease of manufacture
If traditional QFN package structure is used without protrusion control, then the manufacturing process is simpler, but automated optical inspection becomes difficult due to solder protrusions
Solution Approach 1:
The patent applies local quality by creating a protrusion prevention structure at specific locations where solder joints are formed. The insulating coating is positioned locally at the flank surfaces adjacent to the solder joint areas, preventing solder from forming protrusions that would interfere with optical inspection, while maintaining simplicity in other manufacturing areas.
3Difficulty of detecting and measuring
If concave is formed on lead frame by etching method to enable automated optical inspection, then inspection becomes possible, but position of lead frame is limited and process complexity increases
Solution Approach 1:
The patent introduces an insulating coating as an intermediary element that enables automated optical inspection without requiring complex etched concaves in the lead frame structure. The insulating layer acts as a visual reference or barrier that facilitates optical detection of solder joint quality, simplifying the overall device structure compared to etched concave approaches.
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
The solution allows for effective solder coating on the power module's side wall, preventing oxidation and enabling reliable automated optical inspection by ensuring a flat, conductive interface between the thermal conduction structure and the board.
Implementation Method 1
a first metal re-distribution layer is formed to connect the insulation structure, the first metal layer and the second metal layer
Implementation Method 2
a thermal conduction structure, a first metal layer attached on the electronic component
Data Source
AI summary
A packaging process and a packaging structure of an electronic component are provided. By the packaging process and the packaging structure of the disclosure, the groove of the thermal conduction structure is covered by the first metal re-distribution layer. Therefore, the flank of the thermal conduction structure is easy to coat the conducting material. Moreover, because the flank of the thermal conduction structure is coated, the surface of the flank of the thermal conduction structure is difficultly oxidized. Furthermore, the conducting material between the thermal conduction structure and the board is flat, so that automated optical inspection of the packaging structure is easy to implement.