Additive Lead Frame Surface Modification for Adhesion
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Solution Overview
Problem
Conventional lead frame packaging of semiconductor devices faces challenges with adhesion of die attach material, mold compound, and wire bonds to the surface of the lead frame, requiring costly plating or micro-etching processes for surface roughening.
Innovation Solution
The use of additive deposition techniques, such as inkjet printing, to apply metal or polymer inks that form solid residues or pillars on the lead frame surface, creating selective roughening or surface energy modifications to enhance adhesion and containment of materials like solder and die attach compounds, reducing the need for aggressive plating or etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional aggressive electrolytic plating or micro-etching is used to roughen the lead frame surface, then adhesion of die attach material and mold compound is improved, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent changes the surface properties of the lead frame by depositing metal particles and controlling their sintering parameters (temperature, time, atmosphere) to create a roughened surface with enhanced adhesion. This alternative approach modifies physical parameters (surface morphology) without requiring complex plating or etching processes
Solution Approach 2:
The invention creates a composite surface structure by depositing metal particles (such as palladium, platinum, or nickel) onto the lead frame surface. This composite layer combines the roughness needed for adhesion with the metallic properties for electrical conductivity and solderability, replacing the need for multi-step plating processes
2Reliability
If global roughening of the lead frame surface is applied, then adhesion is improved, but manufacturing cost increases due to aggressive plating steps
Solution Approach 1:
The patent applies surface roughening selectively to specific regions of the lead frame where adhesion is needed (such as die attach areas and wire bond pads) rather than globally roughening the entire surface. This localized approach reduces material consumption and manufacturing cost while maintaining adhesion performance where required
Solution Approach 2:
The invention uses metal particle deposition that can be applied through printing or spraying techniques, creating a replicated rough surface structure. This method is more cost-effective than traditional aggressive plating while achieving the same adhesion enhancement effect
3Reliability
If metal ink is sintered to create rough surface structures, then adhesion and containment of materials are improved, but process time increases
Solution Approach 1:
The patent employs periodic or pulsed heating during the sintering process to rapidly heat and cool the metal particles. This pulsed sintering approach reduces overall process time compared to continuous slow sintering, while still achieving the desired rough surface morphology and adhesion properties
Solution Approach 2:
The metal particle deposition process serves multiple functions simultaneously: it creates surface roughness for adhesion, provides electrical conductivity, enables solderability, and creates containment structures. This multi-functionality reduces the need for separate process steps, thereby reducing total manufacturing time
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
This method provides a cost-effective and area-selective surface modification that improves adhesion and containment of materials, reducing yield loss and reliability issues while maintaining the structural integrity of the semiconductor devices.
Implementation Method 1
The ink can be, for example, a sinterable metal ink or a UV-curable polymer or a UV-curable polymer-based mixture
Implementation Method 2
an ink that is either solid (e.g., particles, such as nanoparticles) or a precursor for a solid that forms a solid (e.g., particles) upon curing or sintering to remove its liquid carrier
Implementation Method 3
to remove its liquid carrier including a solvent and/or dispersant
Implementation Method 4
Selective roughening structures aid in adhesion of the die attach material, mold compound, wire bonds, or solder to the surface of the substrate
Data Source
AI summary
A method of lead frame surface modification includes providing at least one pre-fabricated metal lead frame or package substrate (substrate) unit including a base metal having a die pad and a plurality of contact regions surrounding the die pad. An ink including a material that is a solid or a precursor for a solid that forms a solid upon a curing step or a sintering step that removes a liquid carrier is additively deposited including onto at least one of (i) a region of the die pad and (ii) at one region of at least a first of the contact regions (first contact region). The ink is sintered or cured to remove the liquid carrier so that a substantially solid ink residue remains.