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test&measurementZONE Products for the week of February 4, 2008
Agilent Technologies Says…
Industry-first DDR2 and DDR3 Ball-Grid Array Probes for Oscilloscopes and Logic Analyzers
Dynamic random access memory (DRAM) data rates have increased significantly over the past few years. Hence, the signals are now operating at a faster speed in a smaller package, which requires a more reliable tool for validating the memory systems. Agilent's new DDR BGA probe provides direct access to the balls of the DRAM with low loading and minimal impact to signal integrity. The probes are used with the oscilloscopes and logic analyzers to perform physical layer and functional test.
The Agilent DDR2 and DDR3 BGA probes provide signal access points to the clock, strobe, data, address and command signals of the DDR3 DRAM for true compliance testing with an oscilloscope. The logic analyzer provides timing and protocol view of the DRAM activities. The DDR2 BGA probe enables simultaneous access to the oscilloscope and to the logic analyzer's full compliance and protocol validation.
"Engineers need to access memory buses with measurement tools that provide high signal-integrity performance and protocol validation," said Sigi Gross, vice president and general manager of Agilent's Digital Test Division. "Both the DDR2 and DDR3 BGA probe adapters meet their needs. We are ready with the tools---including the DDR3 test application we launched recently---that will help engineers validate their designs quickly and easily."
The DDR2 BGA probe provides probing of x8 and x16 DRAM packages. Model numbers W2631A and W2632A, when combined with Agilent's E5384A and E5826A logic analyzer adapters, support command and data probing for x16 packages; model numbers W2633A and W2634A provide access to command and data buses for x8 packages. When used with high-bandwidth solder-in InfiniiMax probes, all four DDR2 BGA probe variants allow probing with the oscilloscopes.
The DDR3 BGA probe supports different packages. The W2635A x8 BGA probe provides support for x4 and x8 DRAM package. The W2636A x16 BGA probe adapter provides support for x16 DRAM package. Each comes in two different widths---10 mm and 11 mm---to satisfy the different spacing requirements between DRAM chips.
EN-Genius Says…
The JEDEC committee that invented the ball grid-array package left inspection and test in the dust. Plainly put, BGAs are fiendishly difficult to work with. Once reflow-soldered down, you just can't get to those solder balls and traces hidden forever under the chip's package.
 To partially circumvent the problems, you can include dedicated vias or special probe points in your board layout, but these schemes don't always result in good signal integrity, especially at Gbit/s data rates.
Probing at the wrong location, or with excessively long traces, can result in impedance mismatches and resulting reflections, causing non-monotonic edges. The repercussions are likely to be errors in test. You probably won't be able to accurately measure slew rate, or accurately ascertain set-up and hold times. What you see on your scope will be misleading.
Enter the Agilent BGA probe adapters for DDR memories (the double data rate architecture is a 2n pre-fetch architecture with an interface designed to transfer two data words per clock cycle at the I/O pins). These probes look like just the ticket for dealing with DDRs packaged in big BGAs, giving you that much sought after access to clock, strobe, data, address, and command signals on these sometimes onerous packages.
 The JEDEC1 DDR3 spec (JESD79-3A) is defined at the DRAM ball-out, and that's exactly where Agilent's probe adapter provides access to the array. The adapter passes signals from the memory controller chip and DRAM directly to the top of the probe adapter. Once there, the signals can be accessed with ordinary high-bandwidth scope probes, feeding an oscilloscope or logic analyzer. That ensures a high degree of true compliance testing.
The image shows Agilent's W2633A x8 DDR2 BGA command and data probe. It can feed logic analyzers and oscilloscopes. The photo shows the probe mounted on a typical DDR2 DIMM.
There are also buried resistors in these BGA probe adapters. The resistors minimize capacitive loading. Specifically, the resistors connect probed signals to solder pads designed to work with Agilent's InfiniiMax E2677A, N5381A, N5425A, and N5426A differential solder-in probe heads.
In use, the adaptive probes would be soldered between the BGA DRAM under test and your circuit board, or onto a DIMM (dual in-line memory module) card where the DRAM would normally be soldered. The W2635A probe, for example, would give you 20 signal lines and 12 grounds, brought out to SMT-sized pads. The W2636A would bring out 26 signal lines with 14 ground pads.
Supplied without solder balls attached, either probe's design has the circuit board or DIMM footprint on its bottom side and the DRAM footprint top side. The probes are also designed to tolerate Pb-free soldering profiles. However, Agilent cautions users to apply the minimum temperature required for soldering and to use the minimum number of heating and cooling cycles. Depending on the attachment order, you can use either leaded or Pb-free solder.
This attachment process isn't for the faint of heart, however. Agilent recommends attaching these probes during manufacturing of your board. That is, let someone else do it, namely a skilled contract manufacturing operation.
Compliance Test Software
These probes are intended for use with Agilent U7231A DDR3 compliance test software, but that’s not mentioned in Agilent's press release. Using the software, and one of the company's Infiniium 54850 or 80000 Series scopes, the BGA adapter will let you test and characterize DDR3 circuits, with the software automatically configuring the oscilloscope for each test. As I mentioned above, these adapters are compatible with Agilent InfiniiMax differential solder-in probe heads. It all comprises one neat interrelated package.
For its part, the software provides a reasonably user-friendly setup wizard, as well as a reporting mechanism that includes margin analysis. The U7231A test also brings a proven test algorithm for clock test to the party. Agilent claims that will help slash compliance test times.
The software package also uses a technique to provide Read/Write burst signal separation on the same bus in a real-time mode for debug and analysis, and can also analyze the loading effect of an adjacent rank of the same memory channel. In operation, the system's test framework handles characterization through multiple trials. These then display an array of statistics for each measurement, returning the worst measurement value. Margin analysis indicates how close your device comes to passing or failing the test for each specification, and a so-called Advanced Debug feature, as well as debug tools in the associated oscilloscope, are also available to aid in root-cause analysis.
You will also need to run appropriate RAM test reliability software with your memory system. That's required in order to generate random memory bus activity. The most commonly used RAM reliability test is the Memtest package, which runs under Windows or Linux, or even MS-DOS.
Pricing:
W2631A DDR2 X16 BGA command and data probe for logic analyzer and oscilloscope: 4 probe set $1999
W2632A DDR2 X16 BGA data probe for logic analyzer and oscilloscope: 4 probe set $1999
W2633A DDR2 X8 BGA command and data probe for logic analyzer oscilloscope: 4 probe set $1999
W2634A DDR2 X8 BGA data probe for logic analyzer and oscilloscope: 4 probe set $1999
E5384A 46-CH SE ZIF probe for X8/X16 DRAM BGA probe connect to 90-pin logic analyzer cable $1250
E5826A 46-CH SE ZIF probe for X16 DRAM data only BGA probe connect to 90-pin logic analyzer cable $1000
E5827A 46-CH SE ZIF probe for 2 X8 DRAMS data only BGA probe connect to 90-pin logic analyzer cable $1000
W2635A DDR3 X8 BGA oscilloscope probe:10 probe set $1500
W2636A DDR3 X16 BGA oscilloscope probe: 10 probe set $1500
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