FAQ: 2-Pin HBM Testers

2-pin tester simply means that only 2 pins of the device under test (DUT) are contacted during each stress pulse. Practically, that implies that the DUT connections are made either manually by the operator or by a robotic type of automatic mechanical switching. Electrically, a 2-pin tester isolates the “unselected pins” and makes sure they are truly ‘floating’ as described in the ANSI/ESDA/JEDEC JS-001 HBM Standard.

A relay matrix is not described in the HBM Standard but is commonly used for automatic switching. Banks of relays are used to connect the DUT pins to ground or one of several pulse generators, with each DUT pin having its own wiring and relays. In contrast, an automatic 2-pin tester eliminates the complexities of relays and their many interconnections along the pulse path by using the simpler approach of moving two probes to contact the pins to be tested. Because it is less complicated, a 2-pin tester can usually provide a better HBM waveform and improved testing accuracy as well as features such as recording the stress current. Matrix testers can test 2 pins at a time, but that doesn’t make them a 2-pin tester as they don’t effectively float the unconnected pins.

No, actually most manual HBM testers are 2-pin testers. The only new feature for 2-pin testing is the automatic placement of the probes to the DUT pins.

The main speed difference is between the motion time of motorized probes contacting the DUT pins and the time of relay switching. While relays themselves can operate in a little less than 10 ms, the relay system speed is mainly determined by the controlling electronics. Since thousands of relays are involved, shift registers are normally used to control the relays for a net switching time of 150 to 250 ms for all the relays. Flying probes have a speed of 300 to 400 ms for raising them moving to other pins and lowering based on motors that have micron placement accuracy. Users having experience with both types of testers report the matrix based testers are about 25% faster. Pulsing and leakage measurements can add comparable test times.

Due to the simplicity of 2-pin testers they are more consistent in their stress pulse application. There is only one pulse source rather than 8 to 24 with matrix testers. All pin pairs are connected with the same wires. Low parasitics prevent waveform distortions in 2-pin testers. Therefore, the accuracy of the test is higher in 2-pin testers.

The ESDA/JEDEC HBM standard JS-001-2012 Annex B4 explains how to identify a Low Parasitic tester . Testers that produce the same current waveform for all DUT pin combinations including DUTs with internally connected pins are Low Parasitic. The simplicity of a 2-pin tester intrinsically meets this specification and allows for reduction in pin combinations per the HBM Standard. The commonly used relay matrix testers have significant wiring parasitics and are not low parasitic testers. Matrix tester manufacturers recognizing that this is becoming an ever more significant problem are now offering upgrades to partly fix the problem but they can be costly.

All equipment with moving parts require periodic maintenance. For matrix testers the moving relay parts produce relay failures and that is their biggest source of down time and maintenance costs. For 2-pin testers based on standard probe stations they require a mechanical service to renew bearings approximately every five years. The cost of a maintenance contract for 2-pin testers is typically lower than for relay based testers.

With many large IC manufacturers having problems with test quality they determined that an alternative to their existing testers was needed. This was especially critical to the manufacturers of 45 nanometer node and smaller technologies. 2-pin HBM testers are an answer to providing a more accurate HBM test.

New technology 2-pin socketless HBM testers provide a simpler solution using mechanical switching rather than relay matrix switching. Due to this simplicity, the capital equipment cost and the cost of ownership of 2-pin testers is less than a traditional matrix tester. Custom sockets and test boards are not needed with 2-pin testers.