Reinforcing Interposer Assembly for Low-Temperature PCB Soldering
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Solution Overview
Problem
Surface mount technology (SMT) poses a challenge in attaching packaged semiconductor devices to printed circuit boards (PCBs) without exposing them to high reflow temperatures, which can erase data in temperature-sensitive circuits like MRAMs, while low-temperature solder joints are unreliable due to fractures at interfaces and within the solder joint.
Innovation Solution
A reinforcing interposer with conductive pads and preformed low-temperature solder is used to create a reliable attachment between the packaged semiconductor device and the PCB, allowing for reflow at temperatures below 200 degrees Celsius, forming strong solder joints without damaging the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature reflow soldering (>235°C) is used to create reliable solder joints, then solder joint reliability is improved, but temperature-sensitive circuitry (e.g., MRAM data) is damaged or data is erased
Solution Approach 1:
The invention divides the soldering process into two separate stages: first, a preliminary solder attachment is formed at lower temperature to establish basic mechanical and electrical connection; second, a reinforcement solder is applied and reflowed at higher temperature to create strong, reliable joints. This segmentation allows different temperature requirements to be satisfied at different stages, protecting temperature-sensitive circuitry while ensuring final joint reliability.
Solution Approach 2:
The preliminary solder attachment is applied and partially reflowed before the final reinforcement solder is added. This preliminary action creates an initial bond that holds components in place and establishes basic connectivity, allowing subsequent high-temperature reflow of the reinforcement solder to occur without exposing the entire assembly to damaging temperatures from the start.
2Object-affected harmful factors
If low temperature solder materials are used to protect temperature-sensitive circuitry, then thermal damage to circuitry is prevented, but solder joint reliability deteriorates due to fractures at interfaces and within the solder joint
Solution Approach 1:
The soldering process is segmented into two distinct solder applications: preliminary solder that attaches at lower temperature to protect sensitive circuitry, and reinforcement solder that is reflowed at higher temperature to ensure joint reliability. This segmentation resolves the contradiction by assigning different temperature profiles to different solder layers based on their specific functions.
Solution Approach 2:
The invention changes the temperature parameter dynamically during the soldering process by applying solder in stages with different reflow temperatures. The preliminary solder uses lower temperature parameters to protect circuitry, while the reinforcement solder uses higher temperature parameters to ensure reliability, thus adapting temperature parameters to different process stages.
3Strength
If standard Pb-free solder reflow temperature is used, then solder joint strength is improved, but data in temperature-sensitive circuits (e.g., MRAM) is lost
Solution Approach 1:
The soldering process is divided into two stages with different temperature profiles: a first solder attachment at lower temperature that preserves data in temperature-sensitive circuits, and a second reinforcement solder application with higher temperature reflow that ensures strong joints. This segmentation allows strength requirements to be met by the reinforcement solder without exposing sensitive circuits to damaging temperatures.
Solution Approach 2:
The preliminary solder attachment is established before the high-temperature reinforcement solder is applied and reflowed. This preliminary action creates an initial bond that protects sensitive circuits during the subsequent high-temperature process, as the reinforcement solder is applied in a way that minimizes thermal exposure to temperature-sensitive components.
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 ensures the formation of reliable solder joints between the packaged device and the interposer and the PCB at lower temperatures, protecting temperature-sensitive circuitry and reducing stress on the solder joints, thereby preventing data loss and improving joint reliability.
Implementation Method 1
an adhesive layer which exposes the conductive pads, and preformed low-temperature solder material on each of the conductive pads
Implementation Method 2
preformed low-temperature solder material on each of the conductive pads... The device assembly is then reflowed at a temperature of less than 200 degrees Celsius to form reliable solder joints
Data Source
AI summary
A semiconductor device comprises a substrate including a set of interconnect pads, a die mounted on the substrate, wherein the die includes circuitry that cannot withstand typical lead-free (Pb-free) solder reflow temperature during reflow process, and a reinforcing interposer including a first set of interconnect pads and a second set of interconnect pads. Low temperature solder material connects one of the set of interconnect pads on the substrate to a corresponding one of the first set of interconnect pads on the reinforcing interposer. A printed circuit board includes a set of interconnect pads. Low temperature solder material connects one of the set of interconnect pads of the printed circuit board to a corresponding one of the second set of interconnect pads of the reinforcing interposer. The low temperature solder material has a reflow temperature below typical Pb-free solder material.