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EE4800 CMOS Digital IC Design & Analysis
Lecture 12 Packaging, Power and Clock Distributions
Zhuo Feng
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.11
Outline■ Packaging■ Power Distribution■ Clock Distribution
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.22
Packagesg■ Package functions
►Electrical connection of signals and power from g pchip to board
►Little delay or distortionM h i l i f hi b d►Mechanical connection of chip to board
►Removes heat produced on chip►Protects chip from mechanical damage►Protects chip from mechanical damage►Compatible with thermal expansion► Inexpensive to manufacture and test► Inexpensive to manufacture and test
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.33
Package Typesg y■ Through-hole vs. surface mount
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.44
Multichip Modules■ Pentium Pro MCM
►Fast connection of CPU to cache►Expensive, requires known good dice
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.55
Chip-to-Package BondingChip to Package Bonding■ Traditionally, chip is surrounded by pad frame
► Metal pads on 100 – 200 μm pitchp μ p► Gold bond wires attach pads to package► Lead frame distributes signals in package► Metal heat spreader helps with cooling► Metal heat spreader helps with cooling
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.66
Advanced Packagesg■ Bond wires contribute parasitic inductance■ Fancy packages have many signal, power layers■ Fancy packages have many signal, power layers
► Like tiny printed circuit boards
■ Flip-chip places connections across surface of di th th d i hdie rather than around periphery► Top level metal pads covered with solder balls► Chip flips upside downp p p► Carefully aligned to package (done blind!)► Heated to melt balls► Also called C4 (Controlled Collapse Chip Connection)► Also called C4 (Controlled Collapse Chip Connection)
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.77
Package ParasiticsgUse many VDD, GND in parallel– Inductance I
Package
– Inductance, IDD
S S ChipVDD
BoardVDD
Bond Wire Lead Frame
Chip
ignal Pins
PackageCapacitor
ignal Pads
DD
Chip
DD
BoardpGND GND
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.88
Heat Dissipation■ 60 W light bulb has surface area of 120 cm2
■ Itanium 2 die dissipates 130 W over 4 cm2p► Chips have enormous power densities► Cooling is a serious challenge
Package spreads heat to larger surface area■ Package spreads heat to larger surface area► Heat sinks may increase surface area further► Fans increase airflow rate over surface area► Liquid cooling used in extreme cases ($$$)
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.99
Thermal Resistance■ ΔT = θjaP
► ΔT: temperature rise on chip► θja: thermal resistance of chip junction to ambient► P: power dissipation on chip
■ Thermal resistances combine like resistors■ Thermal resistances combine like resistors► Series and parallel
■ θja = θjp + θpa
► Series combination
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1010
Example■ Your chip has a heat sink with a thermal
resistance to the package of 4.0° C/W. ■ The resistance from chip to package is 1° C/W.
■ The system box ambient temperature may reach 55° C55° C.
■ The chip temperature must not exceed 100° C.
■ What is the maximum chip power dissipation?■ What is the maximum chip power dissipation?
■ (100-55 C) / (4 + 1 C/W) = 9 W■ (100 55 C) / (4 1 C/W) 9 W
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1111
Temperature Sensor■ Monitor die temperature and throttle performance■ Use a pair of pnp bipolar transistors
► Vertical pnp available in CMOS
lnBEqV
ckTc s BE
IkTI I e VI
= → =
1 2 11 2
2
ln ln ln ln
c
c c cBE BE BE
s s c
q I
I I IkT kT kTV V V mq I I q I q⎛ ⎞ ⎛ ⎞
Δ = − = − = =⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
■ Voltage difference is proportional to absolute temp► Measure with on-chip A/D converter
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1212
Power Distribution■ Power Distribution Network functions
►Carry current from pads to transistors on chip►Maintain stable voltage with low noise►Provide average and peak power demands►Provide current return paths for signals►Avoid electromigration & self-heating wearout►C littl hi d i►Consume little chip area and wire►Easy to lay out
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1313
IR Drop in Power Distribution NetworkIR drop: voltage drop due to non-ideal resistive wires
VDD
XX
VDD VDD
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1414
GNDGND Cadence
Power Delivery NetworkySocket
ChipPackage
C4 Bumps
PCB
Entire Power Delivery Network
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1515
On-Chip Power Delivery Network
Power System Modely■ Power comes from regulator on system board
► Board and package add parasitic R and L► Bypass capacitors help stabilize supply voltage► But capacitors also have parasitic R and L
■ Simulate system for time and frequency responses■ Simulate system for time and frequency responses
V lt P i t d Ci it P k S ldVoltageRegulator
Printed CircuitBoard Planes
Packageand Pins
SolderBumps
Bulk Ceramic Package On-Chip On-ChipV
Chip
BulkCapacitor
CeramicCapacitor
PackageCapacitor
On ChipCapacitor
On ChipCurrent DemandVDD
PackageBoard
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1616
Power Delivery Network Modelingy g
Multi-million nodesThousands of nodes
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1717
On-Chip Power Grid Modeling & Analysis■ Multi-layer interconnects are modeled as 3D RC network
► Switching gate effects are modeled by time-varying current loadings
p g y
Vdd Vdd
Vdd Vdd
■ DC analysis solves linear systemTens of millionsof unknowns !G v b⋅ = :n nG ×∈ℜ Conductance Matrix
■ Transient analysis solves
( )( ) ( )dv tG v t C b t+1
::
n n
n
Cv
×
×
∈ℜ
∈ℜ
Capacitance Matrix
Node Voltage Vector
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1818
( )( ) ( )G v t C b tdt
⋅ + ⋅ =1 :nb ×∈ℜ Current Loading Vector
Power Requirements■ VDD = VDDnominal – Vdroop
■ Want Vdroop < +/- 10% of VDD■ Want Vdroop / 10% of VDD
■ Sources of Vdroop
► IR drops► L di/dt noise
■ IDD changes on many time scalesPower
clock gatingMax
Average
Min
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.1919
Time
Important Metrics I■ Voltage Droop.
► Two sources: IR drops and Ldi/dt noises.► Large voltage droop leads to circuit timing failure or function► Large voltage droop leads to circuit timing failure or function
failure.► Usually only 5% rail is allowed for 90nm or beyond
technologiestechnologies.VDDn
+ ( )dn DD DDn SSnV V V V= − −
5%V V≤
V
Tn
-
Vn5%dn DDV V≤
VSSn
VDD
V V
5%VDDVdn
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2020
VDDn -VSSn
IR Drop■ A chip draws 24 W from a 1.2 V supply. The
power supply impedance is 5 mΩ. What is the IR drop?
■ IDD = 24 W / 1.2 V = 20 AIR d (20 A)(5 Ω) 100 V■ IR drop = (20 A)(5 mΩ) = 100 mV
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2121
L di/dt Noise■ A 1.2 V chip switches from an idle mode
consuming 5W to a full-power mode consuming 53 W. The transition takes 10 clock cycles at 1 GHz. The supply inductance is 0.1 nH. What is the L di/dt droop?the L di/dt droop?
ΔI = (53 W – 5 W)/(1.2 V) = 40 AΔt = 10 cycles * (1 ns / cycle) = 10 nsL di/dt droop = (0.1 nH) * (40 A / 10 ns) = 0.4 V
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2222
Important Metrics II■ Current density.
► High direct current density leads to electromigration phenomenonphenomenon.
► Electromigration decreases reliability or even breaks connections.
/J I w=
I
, , /avg m avg m mJ I w
,avg mJ σ≤Im
I
0
Im
Iavg,
m
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2323
m
Technology Scaling: Challenges
■ Scaled down supply voltage vs. increased operating frequency and power densities.p g q y p► Higher percentage of voltage droops.► Lower voltage droop tolerance.
■ Shrunk chip area vs. increased gated density.► Less wiring resources.► Larger power delivery network dimensions.
■ Fine-grained power management■ Fine-grained power management.► Power gating.► Multiple power domains.
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2424
Technology Scaling: Implications■ Simulation:
► Stricter accuracy requirement.M ffi i t i t f ti d► More efficient in terms of runtime and memory.
► Full chip simulation with package and integrated components.
■ Verification:► Power-gated power delivery network with multiple power► Power gated power delivery network with multiple power
gating configurations.
D i■ Design:► Optimization for wire sizing.► Detailed tradeoff analysis for on-chip voltage regulation.
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2525
► Optimization for on-chip voltage regulation.
Frequency Responsey■ Multiple capacitors in parallel
► Large capacitor near regulator has low impedance at low frequencies
► But also has a low self-resonant frequency► Small capacitors near chip and on chip have low impedance at
high frequencies
■ Choose caps to get low impedance at all frequencies
impeda
f (H )
nce
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2626
frequency (Hz)
Example: Pentium 4■ Power supply impedance for Pentium 4
► Spike near 100 MHz caused by package Ly g
■ Step response to sudden supply current chain► 1st droop: on-chip bypass caps► 2nd d k it► 2nd droop: package capacitance► 3rd droop: board capacitance
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2727
[Wong06]
Clock Distribution■ On a small chip, the clock distribution network is just a wire
► And possibly an inverter for clkb
■ On practical chips, the RC delay of the wire resistance and gate load is very long► Variations in this delay cause clock to get to different elements at
different times► This is called clock skew
■ Most chips use repeaters to buffer the clock and equalize the delay► Reduces but doesn’t eliminate skew
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2828
Example■ Skew comes from differences in gate and wire delay
► With right buffer sizing, clk1 and clk2 could ideally arrive at the same time.
► But power supply noise changes buffer delays► clk2 and clk3 will always see RC skew2 3
3 mm 3.1 mmgclk
0.5 mm
1.3 pF
clk1 clk2clk3
0 4 pF 0 4 pF0.4 pF 0.4 pF
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.2929
Review: Skew Impact
F1 F2
clk clk
Combinational Logic
Tc
Q1 D2■ Ideally full cycle isavailable for work
clk
Q1
tskew
tsetup
tpcq
tpdq
■ Skew adds sequencingoverhead
D2
CLF1
clk
Q1
■ Increases hold time too
F2
clk
D2
( )setup skew
sequencing overhead
pd c pcqt T t t t≤ − + +
Q1
clk
tskew
thold
tccq
hold skewcd ccqt t t t≥ − +
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3030
Q
D2 tcd
ccq
Solutions■ Reduce clock skew
►Careful clock distribution network design►Plenty of metal wiring resources
■ Analyze clock skew►Only budget actual, not worst case skews►Local vs. global skew budgets
T l t l k k■ Tolerate clock skew►Choose circuit structures insensitive to skew
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3131
Clock Dist. Networks■ Ad hoc■ Grids■ Grids■ H-tree
Hybrid■ Hybrid
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3232
Clock Grids■ Use grid on two or more levels to carry
clock■ Make wires wide to reduce RC delay■ Ensures low skew between nearby points■ But possibly large skew across die
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3333
Alpha Clock GridsAlpha 21064 Alpha 21164 Alpha 21264
PLL
gclk gridgclk grid
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3434
Alpha 21064 Alpha 21164 Alpha 21264
H-Trees■ Fractal structure
► Gets clock arbitrarily close to any point► Matched delay along all paths► Matched delay along all paths
■ Delay variations cause skew■ A and B might see big skew
A B
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3535
Itanium 2 H-Tree■ Four levels of buffering:
►Primary driverRepeaters
►Repeater►Second-level
l k b ffclock buffer►Gater
■ Route aroundTypical SLCBLocations■ Route around
obstructions Primary Buffer
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3636
Hybrid Networksy■ Use H-tree to distribute clock to many points■ Tie these points together with a gridp g g
■ Ex: IBM Power4, PowerPC► H-tree drives 16-64 sector buffers► Buffers drive total of 1024 points► All points shorted together with gridp g g
Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 2010Z. Feng MTU EE4800 CMOS Digital IC Design & Analysis 201012.12.3737