Asymmetric Land Structure for MLF Package Reliability
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Solution Overview
Problem
Micro lead frame (MLF) type semiconductor packages face reliability issues due to lands dislodging from the package during manufacturing or attachment to a next level assembly, such as a PCB, which reduces their reliability and functionality.
Innovation Solution
A substrate with a land structure and adhesion pad isolated by an insulating layer, where the land structure and adhesion pad have size variations, with the upper part being larger than the lower part, providing improved locking features and stability through a series of processing steps including half-etching, filling with resin, and plating, to prevent lands from detaching from the package substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional MLF type semiconductor package is fabricated with lands on the lead frame, then the package can be manufactured with standard processes, but the lands become dislodged from the bottom surface during manufacturing or attachment to PCB
Solution Approach 1:
The land structure is designed with asymmetric geometry where the upper part (exposed surface) has a larger area than the lower part (embedded portion). This asymmetric configuration creates a mechanical interlock with the molding compound, preventing the land from being dislodged during manufacturing or PCB attachment processes while maintaining reliable electrical connection.
Solution Approach 2:
The invention transitions from a conventional two-dimensional land surface to a three-dimensional land structure by embedding the land partially into the molding compound. This dimensional change creates depth and volume in the land structure, forming a mechanical interlock that prevents dislodging while maintaining electrical connectivity.
2Reliability
If the land structure is modified with varying sizes (upper part larger than lower part), then locking features are improved and lands are prevented from detaching, but the manufacturing process becomes more complex
Solution Approach 1:
The land structure is segmented into distinct portions: an upper part with larger area for electrical connection and a lower part with smaller area for embedding. This segmentation allows each portion to serve its specific function optimally while being manufactured as an integrated structure through standard lead frame fabrication processes.
Data Source
AI summary
In one embodiment, a method for forming a package substrate includes selectively removing portions of a lead frame to form cavities and filling the cavities with a resin layer to define an adhesion pad and a land structure. Top portions of the lead frame are selectively removed to isolate the adhesion pad and the land structure from each other, to expose a top surface of the resin layer, and to form at least one land having a part with a relatively greater size than the size of a respective lower part.