Question 1

How does FM Tech manage to improve reliability so much?

Accepted Answer

CTE MATCHING is the very core of FM Tech.  Finar Buffer is engineered to provide anisotropic behaviour.  Its internal structure can be described as a self-standing, closely packed pin grid array (CPPGA).  Put another way Finar Buffer is composed of many strands, loosely connected between each other (remember it is self-standing). These strands allow for large displacement between the two tips of each strand and the adjacent tips in each plane. This means that Material A attached to one side of the Finar Buffer can experience thermal dilatation without creating stress between the different tips of the Finar Buffer strands in contact with the plane because the tips have independent spatial elasticity in all, x, y and z directions.Likewise the Material B on the other side of the Finar Buffer is protected from the thermal dilation of Material A by the elasticity in the length of the strands.
 
We underline that a thin and long pin provides improved flexibility in the plane direction and extremely low structural stiffness.  Moreover, the pins do not form a homogeneous structure, they are not straight or in parallel and this further increases the flexibility.
FM Tech can even handle the higher internal temperatures expected with WBGs.

Question 2

How does FM Tech manage to reduce Thermal Resistance so effectively?

Accepted Answer

Finar Buffer, when made of copper, provides thermal conductivity close to that of solid copper.
The main secret though, is down to the “Zero Attach” property of Finar Buffer, this enables it to virtually neutralize the thermal resistance contribution of the attach or filler.  If you consider that the TIM contribution to thermal resistance can count for some 50% of the overall system, this makes the difference.  BUT equally Solder accounts for some 6% and this can be virtually cancelled, this also has an impact!!
Another critical factor is that AlN or high performance ceramics do not need metalization to join with Finar Buffer, so cheap high grade substrate can be cheaply introduced.  As a result, we are able to eliminate these elements when compared to standard architecture, reducing not only Thermal Resistance but also lowering costs.
Finally, all these characteristics work over extremely large areas and with extreme reliability.

Question 3

Does "Zero Attach" work for all of types of attach materials?"

Accepted Answer

We have used Ag sinter, solder, resin and high conductive glue for join attach internally and TIM externally.  Yes, when attach material is put between Finar Buffer and another material it is forced into the interstitial spaces between the pins, or seen another way the pins pierce the attach material, such that between the end of the pin and the facing material there is "Zero Attach".

Question 4

How does FM Tech drive down the cost of production?

Accepted Answer

FM Tech does not use exotic materials nor does Finar Buffer require a complex production process.  Due to the extreme thermal properties of FM Tech, the silicon chip area can be reduced by up to 50% whlst maintinaing the same performance and with an increased lifespan.  Since the chip accounts for some 50% of the cost of the components this is the primary factor. In addition there are economies from a more simplified design and construction process using fewer components with less stringent specifications.

Question 5

At what stage is the industrialization of FM Tech?

Accepted Answer

FM Tech uses widespread, common materials that are typically produced and formed in a highly industrialized factory.  No exotic material is involved nor any complex production process. As no mass production plant has been developed for FM Tech, it is not possible to fully comment on the production process, however, in building the prototypes the production steps have been developed smoothly and only standard equipment has been employed to mechanically assist the prototype production. No obvious bottleneck or critical step in the production process has transpired to date.
 
In our opinion FM Tech allows for enhanced flexibility in power module design, significantly reducing thermal stress and deformation, allowing FM Tech to be easily applied on any device size or scale, greatly reducing the cost for small series, and allowing to reduce machining costs and overall process costs.

Question 6

Has Finar Module done other tests like Hot store, Humidity, Vibration?"

Accepted Answer

Not yet, that said environmental tests are not central to FM Tech and involve other details of the packaging, though we point out that we thoroughly expect FM Tech to be sufficiently vibration and shock resistant.

Question 7

What are the toughest Heat Cycles done to date?

Accepted Answer

We have done 60 cycles at DT 230°C from 20°C to 250°C.  There were no visible signs of warpage.  This test is far beyond the required temperature ranges for existing power module packaging.

Question 8

Can FM Tech reduce baseplate deformation over prolonged power cycles?

Accepted Answer

FM Tech is focused on the thermo-mechanical management of the baseplate, and can offer an outstanding control of baseplate flatness with time and thermal load to allow for a long term constant and reliable thermal contact.

Question 9

SiC chips pose important problems due to higher temperature, stronger temperature gradients and shorter switch on time.  Can FM Tech deal with these challenges?"

Accepted Answer

FM Tech is focused on the thermo-mechanical management of the environment around the chip, it employs materials which do not suffer degradation for high temperature and offer a better control on mechanical strains resulting from high temperature gradients.  As such it is an ideal solution to manage an SiC chip. FM Tech does not focus specifically on low inductance structures but it is not an obstacle either and as such can implement a number of solutions to minimize inductance.  At present the FM Tech's structure inductance has not been measured.

Question 10

Can FM Tech fit in thin power module configurations, discrete packages, capsule packages and even Press Pack packages? Are there dimensional constraints?"

Accepted Answer

FM Tech can find applications down to power discrete element and can fit in thin packaging, eventually down to less than 5mm, mainly depending on baseplate thickness. Similarly, it can be applied to larger devices and deliver exciting capabilities which can have a large impact in terms of absolute performance, reliability, construction flexibility, opening the way to new designs and higher, reliable, affordable power density at all scales.

Question 11

What is the range of thickness of Finar Buffer?

Accepted Answer

Finar Buffer has been prepared successfully with a thickness down to 500um. Structures as lhin as a few 100um are possible, the lowest limit has yet to be investigated.  Finar Buffer as thick as 30mm has been successfully prepared we do not foresee any relevant upper limitation to height.

Question 12

Is Finar Buffer porous and if so to what extent?

Accepted Answer

Finar Buffer is porous it's structure has a large surface to volume relationship.

Question 13

What is the rate of thermal decay of Finar Buffer?

Accepted Answer

Finar Buffer is made of a high density macroscopic Cu structure, we can therefore expect it to have similar behaviour to solid Cu and therefore no thermal decay in the temperature range of powere device operation.

Question 14

What is the in-plane TEC and E-Modulus?  What is the elasticity of Finar Buffer in the z direction?

Accepted Answer

Finar Buffer is an engineered material which offers different properties depending on the applied design. E-Modulus behaviour under compression and under tension is different and is depending on the design but can be several orders of magnitude lower than solid copper.
Roughly speaking E modulus in the x-y plane can be approximated at 600MPa (Mega, not Giga)
At the moment the Ez modulus is roughly the same of xy plane modulus.
Similarly, TEC can be designed to be from nearly zero to nearly copper. We focused on a high thermal conductivity and high reliability application which has a typically extremely low E-Modulus and nearly zero TEC and a thermal conductivity >90% solid Cu.

Question 15

Can you attach Finar Buffer onto a leadframe of a Discrete?

Accepted Answer

Yes, you can easily attach Finar Buffer to any leadframe material.  BUT we can go one better we can produce Finar Buffer in a way to substitute the entire leadframe.

Question 16

Can Finar Buffer have slightly curved or concave topography?

Accepted Answer

Curved / concave topographies are possible with FM Tech, because the structure is compliant.  Concave topolgies can improve connection when pressure is applied.

Question 17

Have you tried using just Alumina between two Finar Buffer layers, to create a hybrid building block?"

Accepted Answer

Yes, our latest prototypes use Allumina simply glued with resin between two strata of Finar Buffer to provide isolation with excellent thermal and resistance results as a result of its "Zero Attach" qualities.  AlN or high performance ceramics do not need metalization to join with Finar Buffer so cheap high grade substrates can be introduced.

Question 18

Is FM Tech compatible with AMB or AlN substrates?

Accepted Answer

Yes!  Finar Buffer CTE MATCHING also works with an AMB or AlN substrate.  AlN or high performance ceramics do not need metalization to join with Finar Buffer so cheap high grade substrate can be introduced. 
 
The use of AIN can provide a further boost to the thermal performance of the architecture. Moreover, since FM Tech significantly reduces substrate thermo-mechanical stress, we expect that the introduction of AIN will unlock its real potential and further improve reliability.

Question 19

Power Module short circuit capabilities are very important as this is a parameter which impacts client’s dimension choice and auxiliary circuitry complexity and size like short circuit detection circuits and eventually snubber circuits. Is there any impact on these elements from FM Tech?

Accepted Answer

Short circuit capability or I2t is connected to short time thermal response of the chip which is significantly improved by FM Tech. Hence we expect a significant improvement of short circuit handling capability which in turn can affect customers choice for reduced nominal current devices which can eventually offer reduced switching capacity reducing the demands for drivers while eventually switch faster reducing switching losses in a positive reinforcing circle. Moreover, when necessary FM Tech can be applied to allow closed-circuit failure mode. Closed circuit characteristics and stability is under investigation.

Question 20

FM Tech has great performance, the only technology that can match it is Mitsubishi T-PM.   Is there any connection between the two technologies?"

Accepted Answer

Mitsubishi T-PM is an outstanding technique to improve thermal design while handling the thermal stresses. Finar Module is moving on a very different direction as it is based on virtually cancelling the thermal stress. Moreover it can use high performance ceramic as substrate and can reduce also TIM contribution for significantly higher performances. In our opinion FM Tech can handle higher temperature and higher power density maintaining extreme reliability, ready for the next generation of WBGs.