TSOPs were firstused to make thin credit card modules for notebook computers.ĬSP (CHIP SCALE PACKAGE)Unlike DIP, SOJ, and TSOP packaging, CSP packaging doesn’t use pinsto connect the chip to the board. TSOP (THIN SMALL OUTLINE PACKAGE)TSOP packaging, another surface-mount design, got its name becausethe package was much thinner than the SOJ design. SOJs are surface-mount components -that is, they mount directly onto the surface of the PCB. SOJ (SMALL OUTLINE J-LEAD)SOJ packages got their name because the pins coming out of the chipare shaped like the letter “J”. They can besoldered in place or installed in sockets. DIPs are through-hole components, which means they installin holes extending into the surface of the PCB. DIP (DUAL IN-LINE PACKAGE)When it was common for memory to be installed directly on thecomputer’s system board, the DIP-style DRAM package was extremelypopular.
Take a look atthe different chip packages below, so you can see how they differ. Newerchips, such as RDRAM use CSP (Chip Scale Package). Some earlier chip designs used DIP (DualIn-line Package) packaging and SOJ (Small Outline J-lead). Today’s most common packaging is called TSOP (ThinSmall Outline Package). The term “chip packaging” refers to the material coating around theactual silicon. Experienced designers arrange, or “lay out,”the traces to maximize speed and reliability and minimizeinterference. The width and curvature of these traces as well asthe distance between them affect both the speed and the reliabilityof the overall module. Traces are like roads thedata travels on. INTERNAL TRACE LAYERThe magnifying glass shows a layer of the PCB stripped away toreveal the traces etched in the board. To learn more aboutthe type of metal on the contacts, refer to the section titled,“Tin versus Gold” on page 67. On some memory modules, these leads are plated with tinwhile on others, the leads are made of gold. Purrfect Memory 1 02 04 CONTACT FINGERSThe contact fingers, sometimes referred to as “connectors” or“leads,” plug into the memory socket on the system board, enablinginformation to travel from the system board to the memory moduleand back.
The followingsection titled “Chip Packaging” shows pictures of chips housed indifferent types of chip packages. Most memory chips have black or chromecoating, or packaging, to protect their circuitry. It’s called “dynamic” RAMbecause it can only hold data for a short period of time and mustbe refreshed periodically. DRAM (DYNAMIC RANDOM ACCESS MEMORY)DRAM is the most common form of RAM. The more space thereis between traces, the lesser the chance of noise interference.This makes the module much more reliable. The more layers a PCBhas, the more space there is between traces. In general, higher qualitymemory modules use PCBs with more layers. Each layer contains traces and circuitry,which facilitate the movement of data. PCB(PRINTED CIRCUIT BOARD)The green board that all the memory chips sit on is actually madeup of several layers. The illustrationbelow shows a typical memory module and points out some of its mostimportant features. In general, itlooks like a flat green stick with little black cubes on it.Obviously, there’s a lot more to memory than that. Memory comes in a variety of sizes and shapes.
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