Manufacturers of ball-grid-array (BGA) burn-in sockets are using a variety of processes to help them keep pace with the testing requirements posed by today's faster and denser integrated circuits. While some vendors are sticking with a stamped metal manufacturing process to produce their sockets, others are using small metal balls to meet the finer lead-pitch requirements of the sockets. Still other BGA socket makers are experimenting with screw machine technology.
At the very finest pitches (0.5 mm), sockets created with stamped metal technology are difficult to mount. "The contacts are so small that they start to lose strength and lack durability," said Brian Abrams, sales and marketing manager at 3M's Test Business, Electronic Handling and Protection Division (Austin, Texas). "It's also difficult to get enough room to open the socket contact," Abrams added. "More people are looking at spring probes, which are bottom-ball contacts, instead of the standard tweezer contact, which grabs the ball at the sides and is popular from 0.65 mm up."
At Semicon West this month, 3M will unveil a 0.65-mm, open-top socket based on stamped metal technology. In the stamped metal manufacturing process, terminals and contacts are stamped in a single piece, then bent as necessary to form the socket.
Advanced Interconnections Corp. (West Warwick, R.I.) has begun shipping 1-mm products based on screw machine technology and is working toward finer-pitch products as well. The company recently announced its True BGA Socket, a 1-mm (0.039-inch)-pitch socket designed to allow a BGA device to be placed directly onto mating contacts. The parts aim to offer a reliable and consistent connection and to eliminate the need for device desoldering at removal.
The socket features a compact, low-profile design that is only 9.5 mm (0.374 inch larger than the device) and co-planarity of less than .006 inch. The sockets are available with either a coin screw or integral finned heat sink.
When surface-mount BGA sockets are soldered to a target BGA pattern, they provide a pluggable interface, and parts can be dropped into sockets for testing and burn-in. The newer parts that need testing may be smaller than their predecessors, and have smaller lead pitches, or they may offer more functionality, packing as many as 800 leads into a 1-mm socket and significantly more in 1.27 mm.
In February, Ironwood Electronics (Eagan, Minn.) introduced a line of high-performance, 1.27-mm-pitch BGA sockets with low clearance and no performance loss. The SK-BGA937A-Z-S-01 and SK-BGA937A-Z-D-01 are zero-insertion-force (ZIF), surface-mountable BGA sockets. They are made for an IBM 06N4604, a 937-pin-count BGA IC (32.5 x 32.5-mm body size, 25 x 25-mm array size and 1.27-mm pitch).
The SK-BGA937A-Z-S-01 surface-mount socket with solder balls can be placed easily on the target board by the flux and surface-mount reflow method, according to Lee Roll, director of marketing. A low-temperature alloy consisting of 63 percent tin and 37 percent lead is used to produce the solder balls.
Other patterns and shapes
Ironwood is also exploring the possibility of offering other BGA patterns and shapes, in addition to a gigahertz BGA socket and a BGA extender. The company's PB-BGA256K-Z-01 probe board (0.8 mm, 17 x 17 array) with ZIF socket is a two-piece adapter. It is designed to simplify IC swap out and provide easy access to all signals while using no more board space than is needed by the IC under test.
The product makes all signals available for probing on .025-inch, gold-plated square posts around the perimeter of the socket. The low-profile, high-density BGA emulation base, SF-BGA289K-B-01, attaches to the target system's BGA in place of the IC, using standard flux and reflow techniques. The two parts plug together via Ironwood's patent-pending interstitial, variable-height terminal pin system, an innovation that provides pluggable interfaces down to 0.75-mm microBGA densities.
The SK-BGA937A-Z-D-01 mounts directly to the target board using up to 80 screws or no screws. Very short connection distances allow for unimpaired system speeds, the company said. The sockets are 2.5 mm larger on a side than the actual BGA package size. Each socket is a precision device, guiding the IC to the exact position for connection. An aluminum heat sink screw provides compressive force.
The sockets use a high-frequency elastomer medium for interconnection and can dissipate power because the body and compression screw are made of aluminum. Operation speed hits 6 GHz. The sockets cost $471 each in 100-piece quantities.
Even in the larger pitches, BGA sockets offer the advantage of allowing a semiconductor to be housed in a package that is only slightly larger than its own size. "We've had 1.27-mm-pitch products for some time, and we keep expanding our offering there," said Gary Eastman, applications manager at Advanced Interconnections.
"Our design goal is to keep the outside perimeter of the socket no more than 2 mm wider than the semiconductor itself. The customer can go back and add a socket to an existing design without having to make any changes, because the part is close enough in physical size to the actual semiconductor," Eastman said.
Demand remains strong for 1-mm and 1.27-mm sockets in characterization, test and burn-in. "I am getting more calls from people needing 1-mm pitch instead of 1.27 mm, and some are even down to .8 mm," said Jim Kudla, sales and marketing manager for Methode Electronics Inc. Connector Products (Rolling Meadows, Ill.). For now, Kudla said, the company will continue to focus on its two-piece, 1.27-mm BGA socketing solution.
A number of devices are available at 1 mm or less (typically .8 or .75 mm). Ironwood, for example, has begun shipping .8- and .75-mm chip carrier and probing adapters. "MicroBGA packages of .8-mm and .75-mm pitch are becoming increasingly common as chip scale packaging techniques reduce overall package sizes," said Roll. "The smaller pitch is especially valuable in handheld, portable products."
Roll added that microBGA devices present several challenges to engineers during product development and testing, as signals are located underneath the IC device and real estate around the chip is often at a premium. Further, replacing defective devices requires rework procedures that can compromise other component connections nearby.
Most of the demand for .5-mm BGA socket solutions is coming from users who want to test memory chips, which have very high I/O levels, noted Joe Bagliere, president of Emulation Technology Inc. (Santa Clara, Calif.). "With too many I/Os at .5 mm, it becomes expensive to route out the pc board. The line and space gaps are so close together that the pcb processes become very expensive. Until that changes, the state of the art for most packages will be .8 mm."
Emulation Technology recently introduced its Silverwings Solderless Socket System, which can handle system operation speeds of up to 9 GHz. The system contains five sockets, available in a variety of pitches (.5 mm, .75 mm, .8 mm, 1 mm, 1.27 mm, 1.5 mm and 2.5 mm) to fit BGA pin counts, lead pitches and grid sizes simply by changing the contact pads and adjusters. The system also includes a heat sink. Applications include development, debug, hand test, programming, qualification and production.
Besides using BGA sockets for testing, many designers have discovered that sockets are ideal for connecting two boards together. "It's a good fit if the customer is attaching a BGA anyway and wants to take that same processing method and use it on the other side of the board as well," said Danny Boesin, marketing director at Samtec USA (New Albany, Ind.). "The sheer density of these connectors is very appealing, and they are also popular in high-speed applications, since the BGA connectors give them plenty of points to use for grounding to improve the speed and performance of the boards."
Samtec offerings
Samtec will introduce a line of mating sockets and terminal sets in a grid array pattern. The SamArray system comprises a high-density connector set with up to 500 I/Os. The 1.27-mm-pitch sockets are available in 5 mm and higher stacking heights with a 25-mm version to be released shortly. The system is available with attached solder balls and features a high-reliability Tiger Eye contact, which is a three-finger, heat-treated beryllium copper contact for high-cycle applications.
Emulation Technology, meanwhile, offers a BGA adapter system that plugs into its BGA base and has balls on top that can be used to solder a daughterboard to the motherboard. "When a motherboard has a lot of expensive chips on it, engineers can take all the expensive high-pin-count chips and put them on another board to keep the motherboard at four layers rather than 18," explained Emulation Technology's Bagliere. "Making a largelayer daughterboard, which is then used with the Emulator Adapter, becomes an efficient way of connecting to large-pin-count packages."
In June, Mill-Max Manufacturing Corp. (Oyster Bay, N.Y.) introduced its BGA Socket/Adapter Systems, which are used for socketing BGA devices and interconnecting circuit boards. The company will offer systems to fit 1-mm and .050-mm grid footprints. A gold-plated beryllium copper "three-finger" contact is press-fit into each mating socket. Sockets and pins are made of brass and plated gold.
A tapered EZ-IN pin for the 0.050-grid systems reduces 0.4N down to 0.08N per pin and is recommended for pin counts over 500.
HAILEY LYNNE MCKEEFRY IS A FREELANCE TECHNICAL WRITER.
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COMPANY CONTACTS
3M Test Business, Electronic Handling and Protection Division
(800) 487-6649
www.3m.com
EETInfo No. 621
Advanced Interconnections Corp.
(800) 424-9850
www.advancedinterconnections.com
EETInfo No. 622
Emulation Technology Inc.
(408) 982-0660 or 1-800-ADAPTER
www.1800adapter.com
EETInfo No. 623
Ironwood Electronics
(800) 404-0204 or (651) 452-8100
www.ironwoodelectronics.com
EETInfo No. 624
Methode Electronics Inc.
(708) 867-6777
www.methode.com
EETInfo No. 625
Mill-Max Manufacturing Corp.
(516) 922-6000
www.mill-max.com
EETInfo No. 626
Samtec USA
800-SAMTEC-9 or (812) 944-6733
www.samtec.com
EETInfo No. 627
