Low Inductance Capacitors Introduction The signal integrity characteristics of a Power Delivery Network (PDN) The ESL of a capacitor determines the speed of energy transfer to a are becoming critical aspects of board level and semiconductor load. The lower the ESL of a capacitor, the faster that energy can be package designs due to higher operating frequencies, larger power transferred to a load. Historically, there has been a tradeoff between demands, and the ever shrinking lower and upper voltage limits around energy storage (capacitance) and inductance (speed of energy low operating voltages. These power system challenges are coming delivery). Low ESL devices typically have low capacitance. Likewise, from mainstream designs with operating frequencies of 300MHz higher capacitance devices typically have higher ESLs. This tradeoff or greater, modest ICs with power demand of 15 watts or more, and between ESL (speed of energy delivery) and capacitance (energy operating voltages below 3 volts. storage) drives the PDN design topology that places the fastest low ESL capacitors as close to the load as possible. Low Inductance MLCCs are The classic PDN topology is comprised of a series of capacitor stages. found on semiconductor packages and on boards as close as possible Figure 1 is an example of this architecture with multiple capacitor to the load. 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 capacitors 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 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). Slowest Capacitors 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 INTERDIGITATED CAPACITORS The key physical characteristic determining equivalent series inductance The size of a current loop has the greatest impact on the ESL (ESL) of a capacitor is the size of the current loop it creates. The smaller characteristics of a surface mount capacitor. There is a secondary the current loop, the lower the ESL. A standard surface mount MLCC is method for decreasing the ESL of a capacitor. This secondary method rectangular in shape with electrical terminations on its shorter sides. uses adjacent opposing current loops to reduce ESL. The InterDigitated A Low Inductance Chip Capacitor (LICC) sometimes referred to as Capacitor (IDC) utilizes both primary and secondary methods of Reverse Geometry Capacitor (RGC) has its terminations on the longer reducing inductance. The IDC architecture shrinks the distance between side of its rectangular shape. terminations to minimize the current loop size, then further reduces inductance by creating adjacent opposing current loops. When the distance between terminations is reduced, the size of the current loop is reduced. Since the size of the current loop is the An IDC is one single capacitor with an internal structure that has been primary driver of inductance, an 0306 with a smaller current loop has optimized for low ESL. Similar to standard MLCC versus LICCs, the significantly lower ESL then an 0603. The reduction in ESL varies by EIA reduction in ESL varies by EIA case size. Typically, for the same EIA size, however, ESL is typically reduced 60% or more with an LICC versus size, an IDC delivers an ESL that is at least 80% lower than an MLCC. a standard MLCC. 74Low Inductance Capacitors Introduction LAND GRID ARRAY (LGA) CAPACITORS LOW INDUCTANCE CHIP ARRAYS (LICA) Land Grid Array (LGA) capacitors are based on the first Low ESL The LICA product family is the result of a joint development effort MLCC technology created to specifically address the design needs between AVX and IBM to develop a high performance MLCC family of of current day Power Delivery Networks (PDNs). This is the 3rd low decoupling capacitors. LICA was introduced in the 1980s and remains inductance capacitor technology developed by AVX. LGA technology the leading choice of designers in high performance semiconductor provides engineers with new options. The LGA internal structure and packages and high reliability board level decoupling applications. manufacturing technology eliminates the historic need for a device to be LICA products are used in 99.999% uptime semiconductor package physically small to create small current loops to minimize inductance. applications on both ceramic and organic substrates. The C4 solder The first family of LGA products are 2 terminal devices. A 2 terminal ball termination option is the perfect compliment to flip-chip packaging 0306 LGA delivers ESL performance that is equal to or better than an technology. Mainframe class CPUs, ultimate performance multi-chip 0306 8 terminal IDC. The 2 terminal 0805 LGA delivers ESL performance modules, and communications systems that must have the reliability that approaches the 0508 8 terminal IDC. New designs that would have of 5 9s use LICA . used 8 terminal IDCs are moving to 2 terminal LGAs because the layout LICA products with either Sn/Pb or Pb-free solder balls are used for is easier for a 2 terminal device and manufacturing yield is better for a decoupling in high reliability military and aerospace applications. These 2 terminal LGA versus an 8 terminal IDC. LICA devices are used for decoupling of large pin count FPGAs, ASICs, LGA technology is also used in a 4 terminal family of products that AVX CPUs, and other high power ICs with low operating voltages. is sampling and will formerly introduce in 2008. Beyond 2008, there are When high reliability decoupling applications require the very lowest new multi-terminal LGA product families that will provide even more ESL capacitors, LICA products are the best option. attractive options for PDN designers. 470 nF 0306 Impedance Comparison 1 0306 2T-LGA 0306 LICC 0306 8T-IDC 0603 MLCC 0.1 0.01 0.001 1 10 100 1000 Frequency (MHz) Figure 2 MLCC, LICC, IDC, and LGA technologies deliver different levels of equivalent series inductance (ESL). 75 Impedance (ohms)