Support-Free Cantilever Leadframe for Electronic Systems

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Solution Overview

Problem

Electronic systems with metal leadframes, used in power switches and voltage regulators, face issues of electrical shorts, delamination of molding compound, moisture sensitivity, and metal corrosion due to exposed metallic supports during assembly, which interfere with board designs and reliability.

Innovation Solution

A temporary pallet is used to support half-etched leadframes during component attachment, providing stability and then removed before encapsulation, allowing components to bridge gaps and stabilize cantilever leads, eliminating the need for exposed metallic supports.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If metallic support bumps and pads are left un-etched during leadframe fabrication to provide physical support during assembly, then the stability of cantilever leads during component attachment is improved, but the risk of electrical shorts, delamination, and moisture ingress increases

Engineering Contradiction:

Improvestability of cantilever leads during assemblyVSAvoidrisk of electrical shorts and delamination

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The invention extracts and removes the problematic metallic support bumps and pads from the leadframe structure. By completely etching the leadframe including areas that would traditionally remain as support features, the patent eliminates the source of electrical shorts, delamination, and moisture ingress while maintaining assembly stability through alternative means (pallet support and component bridging).

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces a pallet as an intermediary support structure during the assembly process. This temporary pallet provides the necessary physical support for cantilever leads during component attachment, replacing the traditional permanent metallic bumps and pads. The pallet is removed after assembly, leaving no residual metallic supports that could cause reliability issues.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If metallic support features are exposed from the encapsulation to support thin cantilever leads, then the ease of assembly is improved, but the interference with board designs and potential for corrosion increases

Engineering Contradiction:

Improveease of component assemblyVSAvoidmetal corrosion and board design interference

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The invention extracts all metallic support features from the final packaged structure by completely etching the leadframe. This eliminates exposed metal surfaces that could corrode or interfere with board designs, while the assembly process is simplified through the use of a reusable pallet that does not become part of the final product.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The pallet used for assembly is designed as a temporary, disposable, or reusable tool that does not become part of the final product. It performs its supporting function during assembly and is then removed, leaving no permanent metallic features that could cause corrosion or board interference issues.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Productivity

If traditional molding encapsulation is used with exposed soldering pads and support bumps, then the manufacturing process is simplified, but the sensitivity to moisture ingress and delamination increases

Engineering Contradiction:

Improvemanufacturing efficiencyVSAvoidmoisture ingress and delamination

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The invention extracts all exposed metallic features from the encapsulation process by completely etching the leadframe. This eliminates the interfaces between metal and molding compound that are prone to delamination and moisture ingress, while the molding process itself remains unchanged and efficient.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention applies different etching depths to different areas of the leadframe, creating a local quality variation where the cantilever leads are thin (for flexibility) and the connection areas are thick (for strength and soldering), without leaving any exposed metallic support features that would compromise reliability.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS8304868B2Multi-component electronic system having leadframe with support-free with cantilever leads

Publication Date: 2012.11.06 TEXAS INSTRUMENTS INC

AI summary

A pallet (501) supporting a half-etched leadframe with cantilever-type leads (403) without metallic supports during the step of attaching components (510) to the leads in order to assemble an electronic system. After assembly, the pallet is removed before the molding step that encapsulates (601a) the components on the leadframe and mechanically supports (601b) the cantilever leads. The pallet is machined from metal or inert plastic material, tolerates elevated temperatures during soldering, and is reusable for the next assembly batch.