tEchnology cooling
➤
same thermal conductivity as pure copper, we believe the resultant reliability and CTE matching will more than make up for this. The cost of manufacturing is also an order of magnitude lower than conventional microchannel coolers, as ours is not a subtractive process.’ Porous copper, however, will have the
same corrosion issues as copper microchannel coolers. One way of mitigating corrosion is by coating the copper with a protective layer, which would be feasible due to the foam’s open cell structure. US company Advanced Cooling
Technologies (ACT) is hoping that coating conventional microchannel coolers could help alleviate some of the problems. It is developing a passivation process that will result in a pin- hole free protective coating for nickel-gold (Ni/Au) plated copper micro-channel coolers. This proposed approach will use atomic layer deposition (ALD) to deposit highly uniform ceramic thin films on commercially available coolers. The ALD coating will provide corrosion resistance and erosion protection for the micro-channel, thereby increasing reliability. To increase the strain tolerance of the ceramic coating and eliminate any pinholes in the coating, the micro-channel surface will be pretreated with an organic self-assembled monolayer. This layer will provide an ideal surface for ALD bonding, improve uniformity by masking surface defects in the metal, and provide compliance for any mismatch in the thermal expansion coefficient. Peter Ritt, vice president of technical services at ACT, says: ‘In my discussions with laser manufacturers, corrosion of microchannel coolers is the
improved thermal management by advanced heatsink design Start at CS-mount
Rth = 0.60 K/W LD-bar
n-contact isolator
p-contact
Reducing height & add nose CH-mount
Add thermal bypass CN-mount
n-contact isolator
Rth = 0.5 K/W p-contact n-contact Rth = 0.3 K/W
Jenoptik’s cn mount technology uses a heatsink on the n-side as well as the p-side of the laser diode bar, giving more efficient cooling Image courtesy of Jenoptik
Number 1 life issue. Our programme is on- going, but we hope to have some results we can share next year. We hope this innovative metal-organic-ceramic combination will allow Ni/Au-plated copper microchannel coolers to transition from primarily laboratory use to an economical means of cooling commercial and military high power laser diode systems.’ Ceramic materials also feature in some
other emerging products in this field. For example, German company Curamik Electronics is using an aluminium nitride (AlN) layer in its ILasCo microchannel cooler to isolate the electrical circuit from the cooling circuit. While this gives a lower cooling performance, it gives a better CTE match to GaAs laser diodes, and means the microcoolers
in an enhanced performance impingement cooler (Epic), the channels carrying the cooling liquid are perpendicular to the surface of the laser. Water impinges (strikes) the surface like an array of fire hoses spraying water on the hot surface Image courtesy of SLT
can be used with standard filtered water, rather than deionised water. ‘Our microchannels are still made in copper, but because the copper is now electronically isolated, there is no electrical corrosion,’ explains product manager Manfred Goetz. ‘We are targeting lifetimes of around 50,000hrs and are currently waiting for feedback from a couple of customers before we officially release the product onto the market.’ Because of the electrical isolation, stacking
the laser diode bars can be a challenge. Curamik has had to increase the width of the package to up to 20mm in order to fit in vias that are capable of feeding 100A through the stack. ‘We know that customers want a direct replacement for conventional copper microchannel coolers, but our solution will require our customers to think a little bigger,’ says Goetz. ‘We realise we will have to work hard to persuade some companies that changing the form factor is worthwhile, but we believe the change is necessary in order to achieve the increased performance.’ While Curamik’s approach is a hybrid
copper/ceramic technology, US company Cutting Edge Optronics (CEO) is going one step further and has decided to move away from copper completely and use an entirely ceramic material instead. ‘We have developed a ceramic microchannel cooler that provides excellent thermal performance and does not require the use of deionised water,’ says Ryan Feeler, sales manager at CEO. The company’s ceramic microchannel
coolers are produced using high-temperature co-fired ceramic (HTCC) technology, which is well-known in the microelectronics industry,
24 ElEctro optics l OCTOBER 2011 ➤
www.electrooptics.com
p-contact isolator
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52