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connectorZONE Products for the week of April 21, 2008
Ironwood Electronics Says…
Extreme GHz Performance Socket for 0.65-mm Pitch LGA 12 x 12 x 0.65 IC
Socket LGA packages with insignificant performance loss and minimal increase in PCB footprint
Ironwood Electronics introduced the new high performance LGA socket for 0.65mm pitch LGA devices. The XG-LGA-7000 sockets are designed for a 12mm package size, operates at bandwidths up to 40 GHz with less than 1dB of insertion loss. The sockets are designed to dissipate up to several watts without extra heat sinking and can handle up to 100 watts with custom heat sink. The contact resistance is typically 50 milliohms per pin.
The XG-LGA-7000 is constructed with high performance and low inductance elastomer with a gold plated, barbed pad connecting to the IC pad. The temperature range is -40 C to +155 C. The pin self inductance is 0.11 nH and mutual inductance of 0.028 nH. Capacitance to ground is 0.028 pF. The socket accommodates IC packages such as the 12X12 LGA with 0.65mm pads in a 17x17 array. Simply attach the socket to the PCB, drop in chip, place lid. Current capacity is 5 amps per pin. In addition the open lid option (XG-LGA-7001) allows probing of die or direct injection of heat or cooling air.
EN-Genius Says…
LGA (land grid array) packages are getting popular, especially for high-end microprocessors. For one thing, LGAs eliminate the risk of missing or damaged BGA (ball grid array) spheres, and LGAs lend themselves to lower profile designs than do BGAs. Eliminating pins also makes for a cheaper package, which is highly significant as processors evolve into devices with 1000 or more I/Os. There's no doubt that demand for LGAs will increase as time goes by, especially for lower cost applications.
 As ICs get faster, dissipation continues to trend upward, too, which is a function of smaller feature sizes internally and concomitant increases in leakage current. For processor makers, increased dynamic current is also required to scale frequency, and multiple cores are now routinely packaged as well. The question is, how do you deal with the heat? One way is to use more pins. Like it or not, more interconnects are typically needed in order to minimize Joule heating and to generally lower interconnect resistance and inductance.
Recall that the power dissipated through Joule heating is a function of the square of the current, and it’s linearly proportional to resistance. Remember, too, that current demand typically increases with each new round of IC process technology that’s rolled out. Ironwood XG-LGA-7000 sockets, designed for ZIF (zero insertion force) test applications, are in lockstep with these trends.
Precision Sockets
Prototyping tools, fixtures, and the like always fascinate. Typically, they're precision one-off devices. Whether it's a special crimping tool or a microwave fixture, they usually carry high price tags, too. The XG-LGA-7000 sockets are no exception. I think of these Ironwood sockets as specialized tools.
Making an LGA test socket with virtually no stray inductance or parasitic capacitance is no easy feat. When I first read the press release, I suspected Ironwood’s new product would be handmade by skilled machinists and technicians. I called the company's director of R&D, Ranjit Patil, to see if I was correct. Sure enough, Patil explained that the sockets are hand crafted of aluminum, with Kapton-film ball-guide interposers at their bottoms.
The target for most vendors is to produce sockets with less than 0.1 nH mutual inductance, less than 0.02 pF mutual capacitance, and pin-resistance values of 20 mΩ or lower. "There are a few vendors offering such LGA sockets," noted Patil. “But most of these sockets only function up to about the 10 GHz to 12 GHz regime."
Ironwood Electronics' socket makes the grade on most of the above requirements, although pin resistance is a bit higher than sockets from some of the company's competitors. Nonetheless, at maximum rated current, you'd see just a 250 mV voltage drop across a pin handling that amperage on an XG-LGA-7000.
High Temperature Operation
The ability to operate over a near-MIL temperature range is probably more significant, especially at the high end, where the Ironwood socket carries a 155°C spec. Although the socket's contact resistance is 50 mΩ per pin, they can dissipate quite a few watts out of the box, and a whopping 100 W if you fit a heatsink. At 40 GHz, that's extraordinary. Handling up to 5 A/pin, without suffering deleterious dimensional instability, is nothing to sneeze at in what's essentially a microwave design.
Patil indicates that the temperature ratings alone make the XG-LGA-7000 sockets useful for extended-temp testing applications in ATE handlers for ICs slated for automotive applications or medical electronics equipment. In addition to accommodating LGAs, you can also use an XG-LGA-7000 for socketing a BGA. That makes them additionally utilitarian and practical.
Unity pricing of the XG-LGA-7000 is $1453 with volume pricing available.
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