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Posted on 01 March 2019

Something New Has Been Added

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Attention all Space, Military, Aerospace, Hi-Rel Power semiconductor users.

A new Power Semiconductor Package, The Ecconowatt, has been designed and the concept patented. It is ceramic, hermetic, surface mountable, lightweight, assembly friendly, with a short cycle time and most importantly, low cost.

By Robert Satriano, CNS Power Ceramix

 

A New Power Semiconductor package has been designed and the concept patented. It is ceramic, hermetic, surface mountable, lightweight, assembly friendly and automatable, with a short cycle time and most importantly,  low cost.

The manufacturing process to produce The Ecconowatt is proprietary and it is the technique used and the experience acquired in ceramics that provides the assurance to allow all the above characteristics to be met. CNS Power Ceramix, A company founded by a business man, a ceramic engineer, and an assembly manufacturing systems and packaging engineer, represent the management. This team is dedicated to producing the Ecconowatt packaging concept in a manner that takes into consideration the Package Manufactures, the Device assembly house, and above all the Users. The package is designed in strip form (5 per strip) Similar to the Plastic Manufacturing System. This allows automatic die attachment and wire bonding operations adequate landing area has been provided to allow multiple wire bonds if necessary.

To 254 versus Ecconowatt

Thermal Resistance is addressed by brazing into the five position strip base a slug of Silicon Cemented Diamond which thermal conductivity is 580 W/mK. Being all ceramic, the strip can be tested in strip form which allows a yield check and discounts the need to assemble a cap on a reject. Ceramic caps and a low temperature Eutectic pre-form material is loaded into a slot in the base strip of five and then vacuum sealed. After sealing the strips are put through a separation fixture which allows the separated devices to be loaded into plastic shipping sticks. The devices can be marked or branded in the stick prior to shipment to the customer. In reading this narrative it should have become evident that CNS management team are confident that this package concept will be used for all Power Semiconductors. As mentioned earlier in this text getting anything new to the market place is a discouraging realization but change is inevitable and will occur when the risk and effort justifies the need.

Section View

The Ecconowatt name was adopted because it represents a product that supplies power at low cost, with absolute reliability. The inventors of the TO-220 plastic encapsulated package named it the Versawatt due to its versatility to various levels of power devices to the users.

The Ecconowatt will be accepted as the package of choice for Power Semiconductors but not before the ultimate users become aware of its existence and demand it for their products. CNS stands ready and waiting to assist all Hi Rel requirement product manufacture with design information. CNS needs your support to get this Ecconowatt style packaging concept to the users.

Power Semiconductor packaging has not had any innovation since the advent of thermo- set plastic encapsulation technology introduction in the 1970's. A few Hermetic packages have surfaced that mimic the plastic package configuration. These packages are expensive, difficult to produce, not assembly friendly and users are clamoring for something new.

Power Semiconductor packaging underwent a change in the 1970's. From hermetic "tin cans" to silicone plastic encapsulated packages. Cost being the major driver, was instrumental in changing over some device users to the plastic package but Reliability did not meet the old "tin can" standards.

A change from silicone plastic to epoxy was a step in that direction. Epoxy, found to improve reliability was now in vogue, however this change did not fully remedy the issue and many users were reluctant to make the change to plastic encapsulated devices. Epoxy brought forth an entirely new set of problems. Wire bonds were being ripped off bond pads on the chip due to the "Glass Transition Temperature" factor creating the coefficient of expansion to accelerate exponentially. Epoxy was a help in many respects but created other issues that had to be addressed. A correction to this issue came with the plastic manufactures filling the epoxy powder with "glass" to lower the "Glass Transition Temperature" to be suitable enough to achieve reliability acceptance. Glass filled epoxy powder gave the Rel community what they demanded and device users were satisfied. Although reliability improved significantly, the factory suffered, molds, post mold tools and all equipment associated with the glass filled epoxy began to quickly show wear and need of replacement. The cost now became the problem. The additional maintainance costs were eating into the margin and demanded immediate attention.

The mold makers used different steel, and applied very expensive coating to the mold cavities which improved the life of the molds and tooling.

Now Product Engineering, Reliability Engineering, the factory, and device users were at a point where they considered the Plastic Encapsulated Semiconductor to be "Good Enough", However continued Rel testing revealed that since these devices were not hermetically sealed the solder used to attach the power chip to the copper lead frame was being attacked by O². It was found that after power cycling, micro cracks formed in the solder under the chip and continue to propagate until finally the chip is severed from the base. The device continues to function due to the compression forces of the epoxy exerted upon the chip to maintain contact with the base. Although this condition is troublesome no one has voiced a concern since the Rel data did not change.

Weight and Thermal Comparison

Hermetic packaged Power device sales began to decline giving way to the plastic system. Device users for Space, Hi Rel, and Military applications began to show an interest in "New" Hermetic packaging concepts that allow the leads to exit the top and side of the package similar to the plastic version as opposed to the old "tin cans" having the leads protrude from the bottom side. After years of continued requests this type package was offered to the Military, Space, and Hi Rel users. A typical design is the JEDEC outline TO- 254. Although, this package met the lead requirement to exit the top side of the package and matched the appearance of its plastic cousin, it was not assembly friendly. Nevertheless, this design was becoming acceptable regardless of cost, difficulty in device assembly and package fabrication. Since volumes for these devices were low and cost not a factor for Hi Rel, Military and Space users this geometrical configuration thrived.

The package was plagued with considerable problems which dealt primarily with hermeticity and therefore changes had to be made which only added to the cost. An acceptable manufacturing process was finally established that satisfied reliability and hermeticity requirements but not without paying the penalty of cost. The cost of the TO- 254 when first introduced ranged in the neighborhood of $28 each. It now sells for $4-$6 at a volume level of 50,000 per month.

To 254 versus Ecconowatt 2

It is evident that the users of this TO-254 concerned themselves only with the fact that the package was hermetic which connotes reliability and paid the price to acquire the product.

Being acquainted with the evolution of Power Semiconductor Packaging and how passionate the engineers were who invented and generated these geometrical configurations, it displeases me to see the "Its Good Enough" attitude prevail because to make a change in a packaging design and have it accepted is a monumental task.

Selling any new concept, passing reliability, passing customer qualification is enough to discourage change because it takes perseverance and a lot of blood, sweat and tears to get anything new and different into customer products. This discouraging realization is paramount in having an new power semiconductor package emerge.

CNS feels very strongly that once this package gets into the hands of device manufacture and users, it will ultimately become the choice for all power semiconductors. The design lends itself to high volume production and will compete with plastic encapsulated packaging costs at the high volume levels. Please contact CNS at the email address below and share with us your needs as we are totally committed and prepared to help. Currently the Ecconowatt is being considered for the automotive ignition circuit driver which only tells you about the flexibility of its design.

 

 

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