Microelectronic Assemblies with Lid Cavities and Interposer Vias
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Solution Overview
Problem
Microelectronic assemblies face failures due to thermal stresses caused by mismatched coefficients of thermal expansion between semiconductor dies and wiring substrates, leading to cracking and detachment of connections, and existing solutions like underfill and lids often introduce additional warpage and stress during the manufacturing process.
Innovation Solution
Attaching a lid made of semiconductor material with a matching coefficient of thermal expansion to the microelectronic module before underfill deposition, and using an interposer with conductive vias and a redistribution layer to buffer the thermal mismatch between the die and the substrate, while forming trenches for precise lid placement and reducing adhesive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If underfill is introduced to reduce thermal stresses on connections, then connection reliability is improved, but warpage of the assembly increases
Solution Approach 1:
The lid is attached to the die before underfill deposition, establishing a pre-assembled unit with matched thermal expansion properties. This preliminary action ensures that the thermal stress buffer is in place before the underfill is applied, allowing the underfill to cure without causing excessive warpage while still providing connection reliability.
Solution Approach 2:
The lid acts as an intermediary element between the die and the underfill/substrate system. By attaching the lid first, it mediates the thermal expansion mismatch, allowing the underfill to be applied without transmitting excessive warpage forces to the connections while still maintaining connection integrity.
2Strength
If lid is attached after underfill curing to strengthen the assembly, then assembly strength is improved, but residual stress increases and may cause later failure
Solution Approach 1:
The lid is attached to the die before underfill deposition and curing, rather than after. This preliminary attachment ensures that the lid and die form a pre-assembled unit with matched thermal expansion properties before the underfill is applied, avoiding the introduction of residual stress that would occur if the lid were attached after curing.
Solution Approach 2:
The lid serves as a beforehand cushioning element that compensates for thermal expansion mismatch between the die and substrate. By being attached in advance, it provides continuous stress buffering throughout the underfill curing process and subsequent thermal cycling, preventing residual stress accumulation that could lead to later failure.
3Shape
If lid is pressed hard against warped assembly to straighten it, then assembly flatness is improved, but connections may break
Solution Approach 1:
The lid is attached to the die before underfill deposition, creating a pre-assembled unit that maintains its relative positioning throughout the process. This eliminates the need for subsequent pressing operations that would be required if the lid were attached after underfill curing, thereby avoiding connection damage while still achieving assembly flatness.
Solution Approach 2:
The lid acts as an intermediary that maintains the structural integrity of the die-substrate assembly during underfill curing. By being attached in advance, it provides a stable reference frame that prevents excessive warpage without requiring hard pressing operations that could break connections.
4Strength
If underfill is applied in liquid form and then cured, then die is attached to substrate, but underfill shrinkage causes warpage
Solution Approach 1:
The lid is attached to the die before underfill deposition and curing. This preliminary action creates a pre-assembled unit with matched thermal expansion properties, which serves as a stable foundation during underfill curing. The lid's presence during curing helps distribute and mitigate the warpage caused by underfill shrinkage while still achieving strong die-to-substrate attachment.
Solution Approach 2:
The lid acts as an intermediary element during the underfill curing process. By being attached in advance, it mediates the warpage forces generated by underfill shrinkage, distributing these forces in a way that maintains both die-to-substrate attachment strength and assembly flatness.
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 approach reduces thermal stresses, minimizes warpage, and enhances the reliability of microelectronic assemblies by matching the thermal expansion coefficients and providing a buffer with the interposer, allowing for stronger and more stable connections.
Implementation Method 1
thermal stresses, i.e. mechanical stresses caused by thermal expansion and contraction that may occur during manufacture and subsequent use
Implementation Method 2
buffer the thermal mismatch between the die and the substrate
Data Source
AI summary
Die (110) are attached to an interposer (420), and the interposer/die assembly is placed into a lid cavity (510). The lid (210) is attached to the top of the assembly, possibly to the encapsulant (474) at the top. The lid's legs (520) surround the cavity and extend down below the top surface of the interposer's substrate (420S), possibly to the level of the bottom surface of the substrate or lower. The legs (520) may or may not be attached to the interposer/die assembly. In fabrication, the interposer wafer (420SW) has trenches (478) which receive the lid's legs during the lid placement. The interposer wafer is later thinned to remove the interposer wafer portion below the legs and to dice the interposer wafer. The thinning process also exposes, on the bottom, conductive vias (450) passing through the interposer substrate. Other features are also provided.