Chemical Anchoring of Mold Compound on Copper Lead Frames
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Solution Overview
Problem
Existing semiconductor packages experience delamination between the mold compound and the die pad or conductive members, leading to diminished structural and functional integrity.
Innovation Solution
A conversion coating solution comprising a salt of zirconate or vanadate with a complexing agent is used to chemically bond the mold compound to a copper lead frame, or a copper tungsten layer is electroplated to create chemical bonds with the mold compound, enhancing adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional physical adhesion methods are used to bond mold compound to lead frame, then manufacturing process is simple, but adhesion strength is insufficient leading to delamination
Solution Approach 1:
A conversion coating layer comprising zirconate, vanadate, or both is applied to the lead frame surface to serve as a chemical intermediary between the mold compound and the lead frame. This coating layer contains reactive functional groups that form chemical bonds with the mold compound, significantly enhancing adhesion strength while maintaining process simplicity through immersion or spray application methods.
Solution Approach 2:
The surface chemistry of the lead frame is fundamentally changed by applying a conversion coating that transforms the inert metal surface into a chemically reactive surface. The coating layer introduces functional groups with different chemical properties that can form strong chemical bonds with the mold compound, changing the interaction mechanism from physical to chemical adhesion.
2Reliability
If conversion coating is applied to enhance adhesion, then adhesion strength improves significantly, but manufacturing process complexity increases
Solution Approach 1:
The conversion coating acts as a chemical bridge that reliably bonds the mold compound to the lead frame, preventing delamination and maintaining structural integrity throughout the product lifecycle. The coating layer's chemical composition is specifically designed to provide reliable adhesion under various environmental conditions.
Solution Approach 2:
The conversion coating process is designed to be self-regulating, where the coating automatically forms the appropriate thickness and chemical composition through controlled chemical reactions with the lead frame surface. This self-service characteristic reduces the need for complex process control and manual intervention, maintaining manufacturing ease.
3Reliability
If conventional bonding methods are used, then manufacturing cost is low, but delamination occurs reducing product quality
Solution Approach 1:
The bonding mechanism is replaced from mechanical/physical adhesion to chemical adhesion through the conversion coating. Instead of relying on mechanical interlocking or weak physical bonds, the coating forms chemical bonds with the mold compound, providing reliable bonding without complex mechanical structures or processes.
Solution Approach 2:
The bonding mechanism parameter is fundamentally changed from physical to chemical interaction. The conversion coating modifies the surface energy, chemical reactivity, and bonding characteristics of the lead frame, enabling reliable adhesion through chemical bonds rather than weak physical forces.
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 chemical anchoring techniques significantly improve adhesion strength between the mold compound and the lead frame, achieving superior adhesion strengths of approximately 4.5 N/mm² and 3.9 N/mm² respectively, compared to traditional methods.
Implementation Method 1
forming a conversion coating solution comprising a salt of a vanadate, a salt of a zirconate, or both with a complexing agent; cleaning a copper lead frame, wherein the cleaned copper lead frame comprises copper oxide on an outer surface thereof; immersing the cleaned copper lead frame in the conversion coating solution
Implementation Method 2
An adhesion strength at an interface between the mold compound and the at least the portion of the outer surface of the copper lead frame is increased relative to a same assembly formed without immersing the copper lead frame in the conversion coating solution
Implementation Method 3
a copper tungsten layer is electroplated to create chemical bonds with the mold compound, enhancing adhesion
Data Source
AI summary
In examples, a method of forming a semiconductor package comprises forming a conversion coating solution comprising a salt of a vanadate, a salt of a zirconate, or both with a complexing agent; cleaning a copper lead frame, wherein the cleaned copper lead frame comprises copper oxide on an outer surface thereof; immersing the cleaned copper lead frame in the conversion coating solution; rinsing the copper lead frame; and forming an assembly by coupling a semiconductor die to the copper lead frame, coupling the semiconductor die to a lead of the copper lead frame, applying a mold compound onto at least a portion of the outer surface of the copper lead frame, and curing the mold compound. An adhesion strength at an interface between the mold compound and the at least the portion of the outer surface of the copper lead frame is increased relative to a same assembly formed without immersing the copper lead frame in the conversion coating solution.