Part 9, Packaging to Protect the Chips from External Elements

Semiconductor chips are tested to sort out defective products before being released as products. Last time, we looked into the “Electrical Die Sorting (EDS)” process which takes place at the completion stage of a wafer. We’ve reached the final part of our series on Eight Essential Semiconductor Processes: the “packaging” process which every chip must make it through to become a perfect semiconductor product. Packaging: Electrically connecting and protecting semiconductor chips from the elements The wafer completed through the previous steps are cut into individual semiconductor chips. Each of these individually cut chips is called a bare chip or a die. But at this stage the chip is unable to exchange electrical signals with the outside and is vulnerable to damage from external impact. For a semiconductor chip—an integrated circuit—to be mounted on a substrate or electronic device, it first needs to be packaged accordingly. The process by which “roads” are made for the semiconductor chip to exchange signals with the outside world and protect it from various external elements is called “packaging.” The aim of packaging is to connect the integrated circuit to an electronic device, and to protect the circuits from elements: high temperatures, high humidity, chemical agents, impact, and vibration. Let’s dive right in, shall we? 1) Wafer cutting

▲ Individually cut chips

First, the wafer needs to be separated into individual chips. A wafer is packed with hundreds of chips, each chip marked out by scribe lines. A diamond saw or laser beam is used to cut the wafer along these scribe lines. Water cutting is otherwise referred to as “wafer sawing” or “wafer dicing.” 2) Die attach

▲ The lead frame functions as a support for the chips

The diced or sawed chips are moved onto a lead frameor printed circuit board (PCB). A lead frame works as a frame that protects and supports the chips, transmitting electrical signals between the semiconductor chip and external circuits. 3) Wire bonding

Connecting the contact point of the semiconductor chip placed on a substrate with the contact point of the substrate using a thin wire to impart electrical properties to the chip is called wire bonding.

▲ Comparison between the wire bonding and flip chip methods

Aside from the traditional wire bonding method, there is another packaging method where the circuits of the chip and substrate are connected using ball-shaped bumps. This improves semiconductor speed. This technique is called flip chip packaging and results in lower electrical resistance, faster speeds, and small form factor capability, compared to wire bonding. The bumps are usually made of gold (Au) or solder (a compound of tin, lead and silver). 4) Molding

▲ Molding: Sealing in the chip with a chemical resin

Once the wire bonding step is complete, it’s time for the molding step. Molding finishes the chip package in the desired shape and protects the semiconductor integrated circuit from physical elements such as heat and humidity. The wire bonded chip is sealed using a chemical resin, and with that the semiconductor chip as we know is completed. The package test: One last step toward the perfect semiconductor chip

▲ Packaged semiconductor chips. Completed chips are subjected to final testing before they are released for a wide range of use in everyday applications

At long last, the semiconductor chip has been completed. After packaging comes the package test to sort out defective semiconductor chips. This test is also called the final test, as it is performed on the finished product. The semiconductor chips are placed in a tester and subjected to various voltages, electrical signals, temperatures and varying levels of humidity to test the product’s electrical properties, functional properties, and operating speed. The data from the tester is analyzed and fed back into the manufacturing or assembly processes, further improving product quality. That ends our series on the eight essential processes that produce semiconductor chips. The processes required to slice silicon ingots into round wafers and turn them into the chips no larger than a fingernail that we find all around us are more intricate and complex than we may have thought. Although mostly hidden, semiconductors are all around us. And the progress of semiconductor technology promises to further enrich our lives.