Cavity Semiconductor Package Two-Step Adhesion Venting
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Solution Overview
Problem
Cavity-type semiconductor packaging faces challenges with blow holes forming during heat curing, which allows contaminants to ingress and compromises the hermetic seal, especially when using conductive lid materials for electromagnetic shielding, and existing solutions like ultrasonic welding may damage fragile MEMS devices.
Innovation Solution
A two-step adhesion process is employed, where a heat curable conductive adhesive is applied partially to allow venting during heat curing, followed by a secondary adhesive that cures at room temperature or under UV to seal the gaps, ensuring a hermetic or near-hermetic seal without damaging MEMS devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat curable conductive adhesive is applied to bond lid to base, then electromagnetic shielding is achieved, but blow holes form during heat curing allowing contaminant ingress
Solution Approach 1:
The bonding process is segmented into two distinct steps: first applying heat curable conductive adhesive for electromagnetic shielding with intentional gaps, then applying secondary adhesive to seal the gaps after curing. This segmentation allows each adhesive to perform its specific function without interference.
Solution Approach 2:
The heat curable conductive adhesive is applied first and cured before the secondary adhesive is applied. This preliminary action establishes the electromagnetic shielding and creates a stable base structure, allowing the secondary adhesive to focus solely on sealing without concern for disrupting the shielding properties.
2Strength
If ultrasonic welding is used to attach lid, then bonding strength is improved, but fragile MEMS devices may be damaged
Solution Approach 1:
The mechanical ultrasonic welding process is replaced with a chemical bonding process using two-step adhesive application. This substitution eliminates the high-energy mechanical vibrations that could damage MEMS devices while achieving comparable or superior bonding strength through controlled adhesive curing.
Solution Approach 2:
The bonding method changes from high-energy mechanical welding to controlled chemical adhesion. By changing the fundamental bonding mechanism from mechanical/thermal to chemical, the process becomes compatible with fragile MEMS devices while maintaining strong lid attachment.
3Object-affected harmful factors
If conductive lid material is used for electromagnetic shielding, then shielding effectiveness is improved, but blow hole formation compromises the seal
Solution Approach 1:
The adhesive application is segmented into two functional zones: the heat curable conductive adhesive provides electromagnetic shielding in specific areas, while the secondary adhesive seals the gaps in other areas. This spatial segmentation allows both electromagnetic protection and hermetic sealing to coexist.
Solution Approach 2:
The solution uses a composite adhesive system combining two different adhesive materials with distinct properties. The heat curable conductive adhesive provides electromagnetic shielding properties, while the secondary adhesive provides superior sealing properties. Together they form a composite bonding system that delivers both functions.
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 effectively prevents blow holes and maintains a secure, hermetic seal while allowing for electromagnetic shielding, suitable for MEMS devices that are sensitive to other attachment methods.
Implementation Method 1
Some lid attachment materials for cavity-type semiconductor packaging, call for heat curing to harden the lid attach material dispensed between the base that includes one or more semiconductor devices and the lid having a cavity in which the semiconductor devices are to reside.
Implementation Method 2
followed by a secondary adhesive that cures at room temperature or under UV to seal the gaps
Implementation Method 3
followed by a secondary adhesive that cures at room temperature or under UV to seal the gaps
Data Source
AI summary
A method (30) of forming a semiconductor package (20) entails applying (56) an adhesive (64) to a portion (66) of a bonding perimeter (50) of a base (22), with a section (68) of the perimeter (50) being without the adhesive (64). A lid (24) is placed on the base (22) so that a bonding perimeter (62) of the lid (24) abuts the bonding perimeter (50) of the base (22). The lid (24) includes a cavity (25) in which dies (38) mounted to the base (22) are located. A gap (70) is formed without the adhesive (64) at the section (68) between the base (22) and the lid (24). The structure vents from the gap (70) as air inside the cavity (25) expands during heat curing (72). Following heat curing (72), another adhesive (80) is dispensed in the section (68) to close the gap (70) and seal the cavity (25).