While most IC handlers cost many times more, a distinct market exists for systems with price tags of less that $200,000. Regardless of how much is paid, these relatively low-cost handlers address the same fundamental job as the more expensive ones—to accurately position a packaged IC so it can be tested. But that’s just the beginning.
You probably need to test a great many ICs, so after the first one has passed or failed, the handler must place it in the appropriate output location to make room for the next untested IC. The output storage medium could be tubes, trays, or tapes, for example, and the handler has to be compatible.
In general, parametric testing will yield a distribution of performance, not just a simple go, no-go decision. The process of deciding to which performance range a device belongs is called binning. Some handlers have the capability to determine 10 or more separate gradations or bins. Grading parts implies the need for permanent marking for identification.
Temperature is a particularly important environmental factor because it can significantly alter the operation of some types of ICs. Consequently, it has become common for handlers to precondition ICs prior to test.
Traditionally, trays of parts may be soaked at low temperature before they are tested. After the test, their temperature is raised to ambient before they are tested again. Finally, a high-temperature test is run.
A recent alternative to this approach directly controls the temperature of each IC as it is presented to the tester. Some systems simply apply a constant temperature block to the IC to force it to the desired test temperature. This technique ensures that the package temperature is close to the required value, but internal dissipation can cause the actual chip temperature to be several degrees higher.
More sophisticated handlers anticipate temperature changes by monitoring the IC power supplies. If the correct amount of heat is removed from the IC package during the time that it is heating up because of additional dissipation, the die temperature can be held nearly constant. This approach is particularly relevant for high-power ICs such as fast microprocessors.
New Packaging Constraints
Handlers obviously do much more than just handle, but even the mechanical aspects of handling are changing. As packages and lead spacing become smaller, maintaining high throughput while manipulating individual parts becomes more difficult. Manufacturers are pursuing several initiatives to provide reliable performance.
Mechanics
Flash from the package molding process can cause jams in the handler mechanism. John Lalley, director of sales and marketing at WTS, explained, “The capability to properly separate the devices when flash holds them together is key to having few device jams. We carefully consider the customer’s devices. Although they may be within the JEDEC specification, they may not run properly through the handler. With miniature small outline package (MSOP) and thin-shrink small outline package (TSSOP) devices, the JEDEC specification is too loose to maintain a low jam rate. Consequently, the machine tracks and running surfaces have to be optimized for the smaller packages.”
The range of package positioning options was described by Kevin Brennan, marketing manager at Delta Design. “The alignment method is determined by the type of package being handled. The simplest approach is to use alignment pins that mate with holes on the contactor or test socket. This works well for packages with leads on only two sides.
“Packages with leads on four sides require a combination of alignment pins and a nest to hold the device,” he said. “For ball grid array (BGA) parts, it’s best to use a precisor that puts the part in a known location before it is picked up and inserted into the contactor.”
Optical sensors are becoming more prevalent in handlers. Regardless of the high degree to which a mechanism has been perfected, optical feedback provides positive verification of component position.
According to Kathryn McClelland, vice president of marketing and sales at Exatron, “We have used optical sensors many years for this purpose. Also, we incorporate redundant monitoring to assure our customers of repeatable, accurate placement. This accuracy preserves the integrity of the leads in the contactor or test socket and ensures correct placement of components in the tray, tube, or tape outputs.”
High-speed parts also influence handler design. It’s not practical to provide only a good mechanical positioning solution if a component’s high operating frequency demands very short lead lengths. The design also must be compatible with an appropriate contactor or test socket if the part is to be tested at speed.
A Different Paradigm
“We are using the latest surface-coating technology for longer life,” said Karsten Mau, vice president of sales and service at Multitest Electronic Systems. “Also, we are developing a strip-format handler that operates in conjunction with final packaging.”
The strip format he refers to is a very recent initiative intended to simplify device handling. A large number of small parts or only three or four very large ICs are packaged and held in position relative to each other by a large lead frame. The lead frame must be designed so that each device can be electrically tested without interference from its neighbors. Otherwise, its function is to hold all the components in precise alignment within a relatively large panel.
Manipulating such a panel is far simpler than attempting to feed thousands of miniscule devices at high speed. On the other hand, high positional accuracy still is required because each lead on each device must be contacted without shorting between leads or causing mechanical damage.
In addition to the Multitest development, Mr. Brennan confirmed that Delta Design was using a vision system to ensure positional accuracy for a test-on-strip handler.
Trends and Economics
Customers are demanding lower cost test solutions, and handlers are feeling the pinch as much as testers. Test-on-strip promises to reduce prices, but changing the packaging/test process takes time. Until manufacturers have fully adopted the new technology, the focus remains on reducing the cost of single device handlers.
Multitest’s Mr. Mau commented, “Handler throughput, reliability, and flexibility are key to driving down the cost of the back-end operation. The Multitest Model MT 9918 achieves up to 36,000 units/h to address the throughput issue. The handler is modular, so customers can quickly reconfigure it to suit different input/output media and device types. Also, it can be used for engineering or high-volume production purposes by putting together only those modules and features needed.”
In most cases, the requirement for less expensive handling solutions is accompanied by an understanding that these need to be more targeted solutions to keep cost down. According to Delta Design’s Mr. Brennan, “If features typically found in higher end machines are needed, the user often is willing to forego other features to keep the handler price low. As an example, device power-dissipation control is needed for a small percentage of packages today. However, the number of packages requiring thermal control is growing, and we will offer this capability as the need for it develops in the market.”
Agreeing that the price of a handler reflects its capabilities, Mike Gillette, director of sales and marketing for Contrel, said, “There has always been constant pressure to reduce cost. To minimize cost, you must decide what features you really need. What can you sacrifice in the way of performance?”
Comparison Chart
A comparison chart of this year’s handlers and similar charts included in EE’s May 1998 handler article shows evolutionary changes. More types of packages are being used today including chip scale (CSP) and power transistor single outline (TO) styles. Where tubes previously dominated the input/output media columns, now a large percentage of handlers support trays and tape-and-reel.
Most of the handlers in this year’s chart are gravity-feed models because pick-and-place machines generally are higher cost. However, as demonstrated by some of the Multitest machines, high throughput and a large-quantity contactor-pin capability can be obtained for less than $200k.
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May 2001