Power Integrity Analysis and Optimization in the Substrate Design

Harini M, Zakir H, Sukumar M

ABOUT CALIBER

Caliber is a fast growing technology services company.

Expertise is High speed PCB, IC package design.

Highly proficient in Signal Integrity, Power Integrity, EMI/EMC analysis.

Specializes in Embedded design services, ATE hardware & Thermal analysis.

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SERVICES

•Pre layout & Post layout•Serial & parallel interface (DDR 2/3/4, gigabit-SERDES)•Co-design (IC/package/board)•IBIS/IBIS-AMI based system SI•Crosstalk, channel loss, s-parameter, eye-diagram, timing analysis

Signal Integrity

•DC Analysis (IR drop, voltage/current distribution, density plots)• AC Analysis ( PDN impedance analysis, target impedance optimization, Transient noise estimation)• Decoupling cap analysis & optimization

Power Integrity

•EMI Radiation•EMI Susceptibility•Compliances to various EMI standards during design phase

EMI/EMC

• Cadence Sigrity PowerDC, PowerSI, optimize PI• Other EDA tools

Simulation Tools

NEED FOR POWER INTEGRITY ANALYSIS?

Modern devices needs higher functionality at lowers possible power => Lower supply voltage

Silicon density doubles every year => increase in core frequency => transient current requirement is getting higher at lower power supply voltages

DC analysis (Cadence Sigrity PowerDC) AC analysis (Cadence Sigrity PowerSI) Decoupling cap optimization (Optimize PI)

SUBSTRATE DESIGN ATE TEST BOARD (silicon wafer testing)

It is a multi layer PCB mounted to the ATE (Automatic Test Equipment) on which the device to be tested is placed.

Probe CardProbe cards are test boards used to test and

measure the IC before packing. It is a testing tool that delivers electrical signals to chips on a wafer by contacting the probes which is fixed on PCB with epoxy. It is an essential inspection device that enables a wafer to be tested by contacting each signal of the tester and pad on wafer with chip unit at the same time.

Probe card types :1. Epoxy Cantilever Probe Card2. Cobra Vertical Probe Card

SUBSTRATE DESIGN Substrate

A substrate is a base material that supports a microelectronic device. It is used in Vertical probe cards as interface between probe card and the wafer. Substrates are called as Vertical space transformers. A space transformer is a major component of a probe card. It provides pitch reduction, high routing density and localized mid-frequency decoupling.

Types of Substrate :Depending on the type of material used, Design and Manufacturing process, the substrates are differentiated as 1. MLO (Multi Layer Organic)2. MLC (Multi Layer Ceramic)

MLC uses ceramic layers that exceed more than 20 layers whereas MLO has organic buildup on both sides of a core.

DC ANALYSIS OPTIMIZATION

Systematic variation of various parameters and show impact of each of them.

Changing the plane layer material (copper -> silver) Increasing trace width in the fanout layer to reduce

DC drop. Increasing plane area (adding 1 or 2 extra power

plane in ceramic layer) Increase via connectivity Increasing the plane thickness

DESIGN#1

24 layer stackup 1-DUTMLC substrateTotal die pin count 936 pinTotal thickness 2.8mm +/- 0.05mm

POWER DOMAINS

IR Drop target for S0_VDD < +/- 1%

IR DROP ANALYSISORIGINAL CASE : with 1 power plane in ceramic layer, copper conductor of 10 um thickness for power planes

CASE1 : ORIGINAL CASE + conductor material changed to silver

=> Change of material makes only 0.1% difference

CASE2 – CASE 1 + thin film layer fanout trace width is increased from 30 um to 90/100 um

=> Fanout trace width increase made significant difference

Hotspot region shown in the thin film layer

CASE3 - CASE 2 + 2 power plane in ceramic layer of 10 um thickness

=> Adding additional plane didn’t help much

CASE3.1 - CASE 3 + improved via connectivity

=> Improving via connectivity made little difference

Improved via connectivity

=> Improving via connectivity make some difference

CASE4 – CASE3 + power plane in ceramic layer of 18 um thickness

=> Now we achieved the target

DESIGN#2

33 layer 3-DUT1623 pins/siteThickness 3.8mm +/- 0.05mm

Similar trends were observed during IR drop optimization process

RESULTS

Similar trends were observed during IR drop optimization process

Z11 ANALYSIS

Case#1: Original layoutCase#2: Adding 1 power planeCase#3: Adding 2 power planeCase#4: Adding extra decoupling capacitors

Original Case#1

Case#2

Case#3

Case#4

Decap report for the best scheme

CONCLUSIONS

Each layout should be seen on case by case basis for AC and DC analysis. Effectiveness of universal rule does not apply.

Systematic analysis was done for DC analysis and AC analysis using Cadence Sigrity tool

Bottleneck is to be found for each new layout for improving IR drop and meeting the target Z.

Increasing fanout trace width and plane layer thickness was found to be most effective in these cases for improving IR drop

Cadence Sigrity tools are very significant tools for doing such kind of analysis quick and efficient.

THANK YOU

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