Package-Integrated Balun Coupler for Low-Loss MM-Wave MMIC Output
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Solution Overview
Problem
Existing mm-wave semiconductor devices face challenges in reducing PCB interconnect losses and optimizing package footprint, particularly in automotive radar applications, due to the need for on-die or in-package BALUNs which are high-loss and limited by metal thickness constraints.
Innovation Solution
A packaged semiconductor device with a balun coupler integrated between the differential output of the MMIC and a single-ended stripline on the package substrate, utilizing a configuration with a ground plane and a stripline transmission line, which provides effective ESD protection and a high common mode rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an on-die BALUN is used to convert differential to single-ended signals, then the PCB footprint is optimized, but the mm-wave losses increase due to limited metal thickness
Solution Approach 1:
The patent moves the BALUN function from the die level (2D plane) to the package substrate level, utilizing the third dimension (thick metal layers in the package substrate) to achieve low-loss mm-wave signal conversion while maintaining compact footprint. The package substrate's multi-layer structure with thick metal provides the necessary dimensional space for effective BALUN operation.
Solution Approach 2:
The package substrate acts as an intermediary between the MMIC die and the PCB, performing the BALUN function in this intermediate layer. This mediator approach allows the thick metal of the package substrate to be used for low-loss signal conversion, while the die itself remains compact and the PCB footprint is optimized.
2Loss of energy
If an in-package micro-strip based BALUN is used to reduce area occupancy, then the mm-wave losses are reduced, but the ball pitch requirement increases to at least 1.5 mm
Solution Approach 1:
The package substrate serves multiple functions simultaneously: it provides mechanical support, electrical interconnection through pillars, and hosts the BALUN function. This multi-functionality allows the design to achieve low mm-wave losses without being constrained by increased ball pitch requirements, as the BALUN is integrated into the substrate's existing structure.
Solution Approach 2:
The patent changes the key parameter of metal thickness by utilizing the package substrate's thick metal layers (typically 17-35 micrometers) compared to on-die metal (1-4 micrometers). This parameter change enables effective mm-wave signal conversion without requiring increased ball pitch, as the thick metal provides sufficient current carrying capacity and signal integrity.
3Loss of energy
If a micro-strip based balun is used to reduce area occupancy, then the mm-wave losses are reduced, but the impedance range becomes limited by packaging design rules
Solution Approach 1:
The patent employs tunable impedance structures in the package substrate that can be adjusted to match different impedance requirements. The BALUN design includes variable geometric parameters (such as trace width, spacing, and length) that can be dynamically optimized during the design process to achieve the required impedance transformation ratio, providing adaptability across different application requirements.
Solution Approach 2:
The package substrate allows for localized optimization of impedance characteristics at different positions. By varying the metal layer configuration, dielectric thickness, and trace geometry in specific regions of the substrate, the design can achieve different impedance values locally while maintaining low overall losses. This local quality approach enables broad impedance range adaptation without compromising the low-loss performance.
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 achieves reduced mm-wave losses, improved ESD protection, and a high common mode rejection ratio, while also allowing for impedance matching and compact device design.
Implementation Method 1
a balun coupler between the differential output, and the single-ended stripline aligned along a second axis; wherein the balun coupler comprises an opening in the first metal layer
Implementation Method 2
Providing the balun integrated with the coupler from die to package may be useful for space-saving, and may give good electro-static-discharge (ESD) protection, since the ground and the signal pin may be galvanically connected, by being shorted on a typically thick ground plane
Implementation Method 3
a second metal layer, therebetween, comprises a single-ended stripline; wherein the stripline transmission line is aligned along a second axis
Data Source
AI summary
Disclosed is a packaged semiconductor device comprising a semiconductor die comprising a MMIC having a differential output; a package substrate, comprising first second and third metal layers, and electrically connected to the semiconductor die by a plurality of pillars between the semiconductor die and the first metal layer, wherein the first and third metal layers comprise a ground plane, and the second metal layer, therebetween, comprises a single-ended stripline; wherein the differential output is galvanically connected to the first metal layer by a pair of pillars aligned along a first axis; wherein the packaged semiconductor device comprises a balun coupler between the differential output, and the single-ended stripline aligned along a second axis; wherein the balun coupler comprises an opening in the first metal layer, the opening comprising two arms extending in a first direction parallel to the second axis.