Down-set leadframe package structure for die alignment
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Solution Overview
Problem
Current surface mount packages with exposed terminations face issues such as die alignment problems during solder attach, material waste in manufacturing, and increased costs due to flip-chip interconnect schemes and under bump metallurgy, which can lead to quality and reliability issues.
Innovation Solution
A down-set leadframe package structure with recessed conductive leads and stand-offs that self-center the semiconductor chip during attachment, reducing misalignment and using an overmolding process to minimize material waste, along with optional undulating leads for enhanced thermal dissipation and a solderable metal structure for reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If single cavity molding processes are used, then manufacturing is simplified, but material waste increases due to mold compound runners and gate regions
Solution Approach 1:
The patent divides the molding process into multiple cavities, where each cavity independently forms a package. This eliminates the need for runners and gate regions that connect single cavities, thereby reducing mold compound waste while maintaining manufacturing simplicity through standardized multi-cavity tooling
2Device complexity
If lead frames with excess material are used, then package structure is simplified, but material waste increases and costs increase
Solution Approach 1:
The patent extracts and removes excess lead frame material after the molding process, keeping only the necessary lead portions that form the package leads. This eliminates waste of unnecessary lead frame material while maintaining the simplified lead frame structure during manufacturing
Solution Approach 2:
The patent discards excess lead frame material that is not needed for the final package structure. By removing and discarding this excess material after molding, the process reduces waste while maintaining structural simplicity during the manufacturing phase
3Reliability
If die attach and solder reflow steps are performed, then electrical connections are established, but die movement occurs causing misalignment
Solution Approach 1:
The patent performs preliminary alignment of the die to the lead frame before the solder reflow process. By establishing precise alignment beforehand and using fixtures or alignment features, the die position is locked in place before heating and soldering occur, preventing movement and misalignment during the thermal processing steps
4Reliability
If flip-chip interconnect scheme is used, then chip connectivity is improved, but manufacturing complexity and cost increase due to UBM and solder bump plating
Solution Approach 1:
The patent extracts and eliminates the need for under bump metallurgy (UBM) layers and solder bump plating processes by using an alternative interconnect method. The lead frame directly provides electrical connections to the die, removing the complex multi-layer metallization structure required in flip-chip configurations
Data Source
AI summary
In one embodiment, a leadless package includes down-set conductive leads having base portions. The base portions include stand-offs that attach to electrodes on an electronic chip using, for example, a solder die attach material. An optional encapsulating layer covers portions of the down-set conductive leads and portions of the electronic chip while leaving pad portions of the down-set conductive leads and a surface of the electronic chip exposed. The pad portions and the surface of the electronic chip are oriented to attach to a next level of assembly.