Low Inductance Capacitors
Introduction
The signal integrity characteristics of a Power Delivery
Network (PDN) are becoming critical aspects of board level
and semiconductor package designs due to higher operating
frequencies, larger power demands, and the ever shrinking
lower and upper voltage limits around low operating voltages.
These power system challenges are coming from mainstream
designs with operating frequencies of 300MHz or greater,
modest ICs with power demand of 15 watts or more, and
operating voltages below 3 volts.
The classic PDN topology is comprised of a series of
capacitor stages. Figure 1 is an example of this architecture
with multiple capacitor stages.
An ideal capacitor can transfer all its stored energy to a load
instantly. A real capacitor has parasitics that prevent
instantaneous transfer of a capacitor’s stored energy. The
true nature of a capacitor can be modeled as an RLC
equivalent circuit. For most simulation purposes, it is possible
to model the characteristics of a real capacitor with one
Slowest Capacitors
capacitor, one resistor, and one inductor. The RLC values in
this model are commonly referred to as equivalent series
capacitance (ESC), equivalent series resistance (ESR), and
equivalent series inductance (ESL).
The ESL of a capacitor determines the speed of energy
transfer to a load. The lower the ESL of a capacitor, the faster
that energy can be transferred to a load. Historically, there
has been a tradeoff between energy storage (capacitance)
and inductance (speed of energy delivery). Low ESL devices
typically have low capacitance. Likewise, higher capacitance
devices typically have higher ESLs. This tradeoff between
ESL (speed of energy delivery) and capacitance (energy
storage) drives the PDN design topology that places the
fastest low ESL capacitors as close to the load as possible.
Low Inductance MLCCs are found on semiconductor
packages and on boards as close as possible to the load.
Fastest Capacitors
Semiconductor Product
VR
Bulk
Board-Level
Package-Level
Die-Level
Low Inductance Decoupling Capacitors
Figure 1 Classic Power Delivery Network (PDN) Architecture
LOW INDUCTANCE CHIP CAPACITORS
The key physical characteristic determining equivalent series
inductance (ESL) of a capacitor is the size of the current loop
it creates. The smaller the current loop, the lower the ESL. A
standard surface mount MLCC is rectangular in shape with
electrical terminations on its shorter sides. A Low Inductance
Chip Capacitor (LICC) sometimes referred to as Reverse
Geometry Capacitor (RGC) has its terminations on the longer
side of its rectangular shape.
When the distance between terminations is reduced, the size
of the current loop is reduced. Since the size of the current
loop is the primary driver of inductance, an 0306 with a
smaller current loop has significantly lower ESL then an 0603.
The reduction in ESL varies by EIA size, however, ESL is
typically reduced 60% or more with an LICC versus a
standard MLCC.
INTERDIGITATED CAPACITORS
The size of a current loop has the greatest impact on the ESL
characteristics of a surface mount capacitor. There is a
secondary method for decreasing the ESL of a capacitor.
This secondary method uses adjacent opposing current
loops to reduce ESL. The InterDigitated Capacitor (IDC)
utilizes both primary and secondary methods of reducing
inductance. The IDC architecture shrinks the distance
between terminations to minimize the current loop size, then
further reduces inductance by creating adjacent opposing
current loops.
An IDC is one single capacitor with an internal structure that
has been optimized for low ESL. Similar to standard MLCC
versus LICCs, the reduction in ESL varies by EIA case size.
Typically, for the same EIA size, an IDC delivers an ESL that
is at least 80% lower than an MLCC.
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Low Inductance Capacitors
Introduction
LAND GRID ARRAY (LGA) CAPACITORS
Land Grid Array (LGA) capacitors are based on the first Low
ESL MLCC technology created to specifically address the
design needs of current day Power Delivery Networks (PDNs).
This is the 3rd low inductance capacitor technology
developed by AVX. LGA technology provides engineers with
new options. The LGA internal structure and manufacturing
technology eliminates the historic need for a device to be
physically small to create small current loops to minimize
inductance.
The first family of LGA products are 2 terminal devices. A
2 terminal 0306 LGA delivers ESL performance that is equal
to or better than an 0306 8 terminal IDC. The 2 terminal 0805
LGA delivers ESL performance that approaches the 0508
8 terminal IDC. New designs that would have used 8 terminal
IDCs are moving to 2 terminal LGAs because the layout is
easier for a 2 terminal device and manufacturing yield is better
for a 2 terminal LGA versus an 8 terminal IDC.
LGA technology is also used in a 4 terminal family of products
that AVX is sampling and will formerly introduce in 2008.
Beyond 2008, there are new multi-terminal LGA product
families that will provide even more attractive options for PDN
designers.
LOW INDUCTANCE CHIP ARRAYS (LICA
®
)
The LICA
®
product family is the result of a joint development
effort between AVX and IBM to develop a high performance
MLCC family of decoupling capacitors. LICA was introduced
in the 1980s and remains the leading choice of designers in
high performance semiconductor packages and high
reliability board level decoupling applications.
LICA
®
products are used in 99.999% uptime semiconductor
package applications on both ceramic and organic
substrates. The C4 solder ball termination option is the
perfect compliment to flip-chip packaging technology.
Mainframe class CPUs, ultimate performance multi-chip
modules, and communications systems that must have the
reliability of 5 9’s use LICA
®
.
LICA
®
products with either Sn/Pb or Pb-free solder balls are
used for decoupling in high reliability military and aerospace
applications. These LICA
®
devices are used for decoupling of
large pin count FPGAs, ASICs, CPUs, and other high power
ICs with low operating voltages.
When high reliability decoupling applications require the very
lowest ESL capacitors, LICA
®
products are the best option.
470 nF 0306 Impedance Comparison
1
0306 2T-LGA
0306 LICC
0306 8T-IDC
0603 MLCC
Impedance (ohms)
0.1
0.01
0.001
1
10
Frequency (MHz)
Figure 2 MLCC, LICC, IDC, and LGA technologies deliver different levels of equivalent series inductance (ESL).
100
1000
REV 01
73
LGA Low Inductance Capacitors
0204/0306 Land Grid Array
Land Grid Array (LGA) capacitors are the latest family of low inductance MLCCs from AVX.
These new LGA products are the third low inductance family developed by AVX. The in-
novative LGA technology sets a new standard for low inductance MLCC performance.
Our initial 2 terminal versions of LGA technology deliver the performance of an 8 terminal
IDC low inductance MLCC with a number of advantages including:
•
Simplified layout of 2 large solder pads compared to 8 small pads for IDCs
•
Opportunity to reduce PCB or substrate contribution to system ESL by using multi-
ple parallel vias in solder pads
•
Advanced FCT manufacturing process used to create uniformly flat terminations on
the capacitor that resist “tombstoning”
•
Better solder joint reliability
APPLICATIONS
Semiconductor Packages
•
Microprocessors/CPUs
•
Graphics Processors/GPUs
•
Chipsets
•
FPGAs
•
ASICs
Board Level Device Decoupling
•
Frequencies of 300 MHz or more
•
ICs drawing 15W or more
•
Low voltages
•
High speed buses
0306 2 TERMINAL LGA COMPARISON WITH 0306 8 TERMINAL IDC
1
Impedance (Ω)
0.1
0.01
0.001
1
10
100
1000
Frequency (MHz)
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051316
DSP and ARM Processors
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