thermal_contactor_faq

What exactly does the compliant thermode do?
The thermode makes thermal contact to a chip under test to allow efficient heating and cooling of the chip by conduction to a thermal transfer fluid. It provides an accurately controlled temperature to allow fast and accurate testing at set temperatures.

Which devices can be tested with the compliant thermode?
The thermode provides effective thermal management for testing high performance devices such as flip-chip BGAs, WLP, e-WLP, bare dice, power devices, and parts with thermal spreaders. Generally speaking, any high power device incorporates an efficient thermal path that can be mated to the compliant thermode.

What is the temperature range of the thermode?
The thermode is rated to operate over a range from -65⁰C to +160⁰C.

What is the economic justification for using a Centipede compliant thermode for testing?
The high thermal conductivity of the compliant thermode improves test yield by reducing tine incidence of hot pots and the accompanying degradation of performance during test. Additionally, the thermode rapidly sets up thermal conditioning of the device under test to cut wasted time on the ATE, and so improving tool utilization.

How does the thermode minimize hot spots?
The thermode provides a uniform surface temperature in intimate contact with the surface of the device under test. Good thermal contact prevents a hot spot from developing in regions of poor contact due to warping or mechanical non-uniformity.

What is the purpose of compliance?
Mechanical compliance allows the contact surface of the thermode to follow the contour of the device under test in order to make intimate thermal contact.

How much compliance does the thermode provide?
The surface of the compliant thermode is a thin membrane capable of flexing under pressure to match a mating surface of the part under test. In practical application the flexibility of the thermode can accommodate device warping of 50-100 microns, depending upon test conditions.

What is the largest size of a compliant thermode available?
Custom thermodes of this design can be made with an active area up to 25 mm square. Larger thermodes, for example a 300 mm wafer chuck, can be made with a design without the gimbal mount feature used in the PAT series of thermodes.

Does the thermode require a special ambient?
The thermode can operate in any gas environment, although a dry gas is recommended in order to prevent condensation when used at low temperatures. Commonly used gases include clean dry air, dry nitrogen and helium.

Why is helium sometimes used as an ambient gas?
The thermal conductivity of helium is higher than that of air by a factor of about six. Use of helium as the ambient gas will improve thermal coupling by about three to four times, depending upon surface topology on the device.

Does the thermode leave a residue on the device?
The thermode makes dry contact to the device, and leaves no residue. The active area of the thermode surface is pure silver, and pure gold or other metals are available as options. No coupling oils, liquids or organic materials are needed for good thermal contact.

What is the service lifetime of the thermode?
The thermode can provide about one million contact cycles without failure, depending upon test conditions and range of compliance needed. Surface contamination on the thermode must be cleaned periodically to prevent damage or embedding of foreign materials into the surface metal.

What is the purpose of the reticulated surface on the thermode?
A honeycomb of fine lines in the surface of the thermode facilitates compliant flexure of the contact membrane. The reticulation provides a path for ambient gas to circulate to and from the active area of the device. This is important in releasing the thermode from the head after test, without suctioning up the device upon release.

Can the compliance of the thermode cause edge or corner cracking of the die?
The center of each honeycomb element kept out of a region within 0.5 mm of a die edge in order to prevent edge damage. Thermal contact is still made to this edge region, but the centers of forces applied to the honeycombs is kept out of the critical edge band.

How does the compliant thermode apply pressure to the device?
Compressed gas pressure in the thermode manifold moves the active area of the thermode into contact with the device. The force of the thermode on the device is regulated and controlled accurately by adjusting this air pressure. After test, the air pressure is released to retract the active area away from the device.

Which coolants can be used with the compliant thermode?
Any coolant such as aqueous mixes, galden®, fluorinert®, organic coolants, silicone, and virtually any liquid. In addition, gases including dry nitrogen, compressed air, and helium can be used. No organic seals or gaskets are used in construction of the thermode.

Does coolant pressure in the thermode affect the force applied to the device?
The design of the thermode employs a balanced force construction in which coolant pressure has no effect on the force or position of the thermode on the device. Coolant pressure up to 100 psi can be used without influencing the thermal contact.

Do pressure pulses in the thermal transfer fluid disturb contact to the device?
No, pressure variations and pulses in the transfer fluid has no significant effect on the shape of the active surface of the thermode.

What materials are used in the thermode?
The thermode is all metal construction, with no organic, magnetic, or toxic materials used.

Can thermal shock damage the thermode?
The thermode can be thermally cycled at a slew rate of 1000 ⁰C per second without damage. Materials used in the thermode are nearly thermally matched to minimize thermal stresses.

How is the thermode mounted in a test setup?
The thermode is mounted in a manifold that supplies thermal transfer fluid to and from the thermode, and provides an enclosure for air pressure used to actuate operation of the device.

Can thermodes be used to test arrays of devices?
Thermodes can be arrayed to test devices in parallel. With suitable manifolds, each thermode in an array can be controlled separately to provide independent thermal management to each device under test.

How fast can the temperature of the thermode be changed?
The low mass of the thermode allows rapid temperature changes for testing at multiple temperatures and to facilitate fast feedback to maintain a set temperature under varying power conditions. The time constant for response is 0.075 seconds, depending upon configuration.

How easy is it to replace the thermode?
The thermode is supplied as a cartridge, with top and bottom O-ring seals to fit a mating manifold. To replace the thermode, a keeper plate is removed from the manifold, and the thermode cartridge is removed. A replacement cartridge is inserted into the manifold and the keeper plate is re-attached.

After replacement, must the thermode be re-aligned?
The thermode is pre-aligned so that no adjustment or alignment is necessary after installation. Flexibility and gimbal action will automatically align the active surface of the thermode to a device under test.

Is the compliant thermode proprietary?
The thermode is manufactured by Centipede Systems under Patents issued and in process.

Is the compliant thermode unique?
The thermode offers the bestthermal contact and response time available in the world today.

Why didn’t I hear about this before?
The Centipede compliant thermode was released for publication at the BiTS 2012 Workshop on March 5 in Phoenix. Contact info@centipedesystems.com for more information on the thermode and its availability.