Wire Bond Via Package-on-Package Assembly for Fine-Pitch Microcontacts
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Solution Overview
Problem
Conventional etching processes are limited in forming microcontacts with a high aspect ratio and arrays of microcontacts with appreciable height and small pitch, which are necessary for advanced microelectronic packaging.
Innovation Solution
A microelectronic package is designed with a substrate having a first and second region, where at least one microelectronic element is mounted on the first surface within the first region, and electrically conductive elements are exposed on the first surface within the second region. Wire bonds with tips having dimensions smaller than the base diameter are formed, and a dielectric encapsulation layer covers portions of the wire bonds, leaving unencapsulated ends for connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching processes are used to form microcontacts, then the manufacturing process is simple and well-established, but the aspect ratio and height of microcontacts are limited
Solution Approach 1:
The patent replaces conventional chemical etching processes with a mechanical wire bonding process to form microcontacts. Wire bonds are bonded to conductive elements on the substrate to create microcontacts with high aspect ratios that cannot be achieved through etching. This mechanical approach enables microcontact heights of 100 micrometers or more with pitches of 50 micrometers or less, overcoming the fundamental limitations of etching processes.
Solution Approach 2:
The patent changes the fundamental parameters of microcontact formation by using wire bonding instead of etching. This allows for unprecedented control over microcontact geometry, achieving aspect ratios greater than 10:1 and heights exceeding 100 micrometers while maintaining small pitches of 50 micrometers or less. The wire bond material, diameter, and bonding parameters can be independently optimized to achieve desired microcontact characteristics.
2Strength
If wire bonds with large diameter bases are used for connection, then mechanical strength is improved, but the pitch of microcontact arrays increases
Solution Approach 1:
The patent applies local quality by creating wire bonds with non-uniform geometry along their length. The wire bonds have larger diameter bases for mechanical strength and connectivity to conductive elements, while the tips are reduced to small diameters for dense array packaging. This gradient in diameter allows the wire bond to fulfill multiple functions: providing mechanical support at the base and enabling small pitch at the tip, thereby resolving the contradiction between strength and array density.
3Reliability
If all wire bonds are fully exposed for connection, then electrical connectivity is maximized, but mechanical protection and insulation are reduced
Solution Approach 1:
The patent applies partial action by selectively encapsulating only the base portions of wire bonds while leaving the tips exposed. The encapsulation layer protects the wire bond bases from mechanical damage and provides electrical insulation, while the exposed tips remain available for electrical connection to subsequent packaging layers. This partial encapsulation approach balances protection with connectivity requirements.
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 solution enables the formation of microelectronic packages with improved mechanical and electrical connectivity, allowing for higher aspect ratio microcontacts and smaller pitch arrays, which enhances the packaging efficiency and performance.
Implementation Method 1
wire bonds having bases bonded to respective ones of the conductive elements
Implementation Method 2
A dielectric encapsulation layer extends from at least one of the first or second surfaces and covers portions of the wire bonds
Data Source
AI summary
A microelectronic package includes a substrate having a first surface. A microelectronic element overlies the first surface. Electrically conductive elements are exposed at the first surface of the substrate, at least some of which are electrically connected to the microelectronic element. The package includes wire bonds having bases bonded to respective ones of the conductive elements and ends remote from the substrate and remote from the bases. The ends of the wire bonds are defined on tips of the wire bonds, and the wire bonds define respective first diameters between the bases and the tips thereof. The tips have at least one dimension that is smaller than the respective first diameters of the wire bonds. A dielectric encapsulation layer covers portions of the wire bonds, and unencapsulated portions of the wire bonds are defined by portions of the wire bonds, including the ends, are uncovered by the encapsulation layer.