Low Inductance Capacitors Introduction The signal integrity characteristics of a Power Delivery capacitor, one resistor, and one inductor. The RLC values in Network (PDN) are becoming critical aspects of board level this model are commonly referred to as equivalent series and semiconductor package designs due to higher operating capacitance (ESC), equivalent series resistance (ESR), and frequencies, larger power demands, and the ever shrinking equivalent series inductance (ESL). lower and upper voltage limits around low operating voltages. The ESL of a capacitor determines the speed of energy These power system challenges are coming from mainstream transfer to a load. The lower the ESL of a capacitor, the faster designs with operating frequencies of 300MHz or greater, that energy can be transferred to a load. Historically, there modest ICs with power demand of 15 watts or more, and has been a tradeoff between energy storage (capacitance) operating voltages below 3 volts. and inductance (speed of energy delivery). Low ESL devices The classic PDN topology is comprised of a series of typically have low capacitance. Likewise, higher capacitance capacitor stages. Figure 1 is an example of this architecture devices typically have higher ESLs. This tradeoff between with multiple capacitor stages. ESL (speed of energy delivery) and capacitance (energy storage) drives the PDN design topology that places the An ideal capacitor can transfer all its stored energy to a load fastest low ESL capacitors as close to the load as possible. instantly. A real capacitor has parasitics that prevent Low Inductance MLCCs are found on semiconductor instantaneous transfer of a capacitors stored energy. The packages and on boards as close as possible to the load. 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 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 The size of a current loop has the greatest impact on the ESL inductance (ESL) of a capacitor is the size of the current loop characteristics of a surface mount capacitor. There is a it creates. The smaller the current loop, the lower the ESL. A secondary method for decreasing the ESL of a capacitor. standard surface mount MLCC is rectangular in shape with This secondary method uses adjacent opposing current electrical terminations on its shorter sides. A Low Inductance loops to reduce ESL. The InterDigitated Capacitor (IDC) Chip Capacitor (LICC) sometimes referred to as Reverse utilizes both primary and secondary methods of reducing Geometry Capacitor (RGC) has its terminations on the longer inductance. The IDC architecture shrinks the distance side of its rectangular shape. between terminations to minimize the current loop size, then further reduces inductance by creating adjacent opposing When the distance between terminations is reduced, the size current loops. of the current loop is reduced. Since the size of the current loop is the primary driver of inductance, an 0306 with a An IDC is one single capacitor with an internal structure that smaller current loop has significantly lower ESL then an 0603. has been optimized for low ESL. Similar to standard MLCC The reduction in ESL varies by EIA size, however, ESL is versus LICCs, the reduction in ESL varies by EIA case size. typically reduced 60% or more with an LICC versus a Typically, for the same EIA size, an IDC delivers an ESL that standard MLCC. is at least 80% lower than an MLCC. REV 01 72Low Inductance Capacitors Introduction LAND GRID ARRAY (LGA) CAPACITORS LOW INDUCTANCE CHIP ARRAYS (LICA ) Land Grid Array (LGA) capacitors are based on the first Low The LICA product family is the result of a joint development ESL MLCC technology created to specifically address the effort between AVX and IBM to develop a high performance design needs of current day Power Delivery Networks (PDNs). MLCC family of decoupling capacitors. LICA was introduced This is the 3rd low inductance capacitor technology in the 1980s and remains the leading choice of designers in developed by AVX. LGA technology provides engineers with high performance semiconductor packages and high new options. The LGA internal structure and manufacturing reliability board level decoupling applications. technology eliminates the historic need for a device to be LICA products are used in 99.999% uptime semiconductor physically small to create small current loops to minimize package applications on both ceramic and organic inductance. substrates. The C4 solder ball termination option is the The first family of LGA products are 2 terminal devices. A perfect compliment to flip-chip packaging technology. 2 terminal 0306 LGA delivers ESL performance that is equal Mainframe class CPUs, ultimate performance multi-chip to or better than an 0306 8 terminal IDC. The 2 terminal 0805 modules, and communications systems that must have the LGA delivers ESL performance that approaches the 0508 reliability of 5 9s use LICA . 8 terminal IDC. New designs that would have used 8 terminal LICA products with either Sn/Pb or Pb-free solder balls are IDCs are moving to 2 terminal LGAs because the layout is used for decoupling in high reliability military and aerospace easier for a 2 terminal device and manufacturing yield is better applications. These LICA devices are used for decoupling of for a 2 terminal LGA versus an 8 terminal IDC. large pin count FPGAs, ASICs, CPUs, and other high power LGA technology is also used in a 4 terminal family of products ICs with low operating voltages. that AVX is sampling and will formerly introduce in 2008. When high reliability decoupling applications require the very Beyond 2008, there are new multi-terminal LGA product lowest ESL capacitors, LICA products are the best option. families that will provide even more 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). REV 01 73 Impedance (ohms)