Semiconductor Manufacturing by Elmer Epistola

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Semiconductor Manufacturing (Page 2 of 2)

by Elmer Epistola

Assembly

The process of putting the integrated circuit inside a package to make it reliable and convenient to use is known as semiconductor package assembly, or simply 'assembly'. Over the years, the direction of assembly technology is to develop smaller, cheaper, more reliable, and more environment-friendly packages. Just like wafer fabrication technology, assembly technology has advanced tremendously that there are now a multitude of packages to choose from.

Despite glaring differences between the various packages available in the industry today, all packages share some things in common. To name a few, all of them: 1) provide the integrated circuit with a structure to operate in; 2) protect the integrated circuit from the environment; 3) connect the integrated circuit to the outside world; and 4) help optimize the operation of the device.

In general, an assembly process would consist of the following steps: 1) die preparation, which cuts the wafer into individual integrated circuits or dice; 2) die attach, which attaches the die to the support structure (e.g., the leadframe) of the package; 3) bonding, which connects the circuit to the electrical extremities of the package, thereby allowing the circuit to be connected to the outside world; and 4) encapsulation (usually by plastic molding), which provides 'body' to the package of the circuit for physical and chemical protection.

Subsequent steps that give the package its final form and appearance (e.g., DTFS) vary from package to package. Steps like marking and lead finish give the product its own identity, improve reliability, and add an extra shine at that.

Assembly Links:

Wafer Backgrind → Die Preparation → Die Attach → Wirebonding → Die Overcoat →

→ Molding → Sealing → Marking → DTFS → Leadfinish

Test

Once assembled, the integrated circuit is ready to use. However, owing to the imperfection of this world, assembled devices don't always work. Many things can go wrong to make a device fail, e.g., the die has wafer fab-related defects, or the die cracked during assembly, or the bonds were poorly connected or not connected at all. Thus, prior to shipment to the customer, assembled devices must first be electrically tested.

Electrical testing of devices in big volumes must be done fast and inexpensively. Mass-production electrical testing therefore requires an automated system for doing the test. Equipment used to test devices are called, well, testers, and equipment used to handle the devices while undergoing testing are called, well, handlers. Tester/handler systems are also known as automatic test equipment (ATE).

Different products require different levels of sophistication in ATE requirements. Electrical testing of voltage reference circuits certainly don't require high-end ATE such as those used to test state-of-the-art microprocessors or digital signal processors. One area of electrical testing that continuously challenge engineers is building an ATE that can test the speed of new IC's that are much faster than what they can use in building their ATE's.

Software written for testing a device with an ATE is known as a test program. Test programs consist of a series of subroutines known as test blocks. Generally, each test block has a corresponding device parameter to test under specific conditions. This is accomplished by subjecting the device under test (DUT) to specific excitation and measuring the response of the device. The measurement is then compared to the pass/fail limits set in the test program. After the device is tested, the handler bins it out either as a reject or as a good unit.

After a lot is tested, it is subjected to other back-end processes prior to shipment to the customer. Tape and reel is the process of packing surface mount devices in tapes with pockets while this tape is being wound around a reel. Boxing and labeling is the process of putting the reels or tubes in shipment boxes, and labeling these shipment boxes in accordance with customer requirements.

Test Links:

Electrical Test → Burn-in → Marking → Tape and Reel → Dry Packing → Boxing and Labeling

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