from the largest ptoducer in the usa
"To remove heat, most Si power transistors are soldered to their substrate with gold/silicon solder. Since AuSi is a “hard” solder, the thermal expansion of the substrate should be between 3 and 10 x 10-6 /°C, in order to prevent cracking of the Si upon temperature cycling. The substrate can either be a dielectric or electrical conductor, depending on the type of transistor. Si VMOS and bipolar transistors must be soldered onto an electrically isolated pad on a thermally conductive dielectric. Materion’s BeO ceramic substrates, known as Thermalox™ BeO, offer a unique combination of high thermal conductivity, high electrical resistivity and low dielectric loss over a wide frequency range. Materion provides hot pressed BeO ceramic substrates, manufactured at its Tucson, AZ facility, to meet this requirement. Materion’s facility in Newburyport, MA then screen prints patterns of thick film MoMn paste that is fired onto the BeO, plated with Ni and then brazed into a package using braze alloys supplied by Materion’s facility in Buffalo, NY.
In the mid-1990’s Motorola invented a new type of RF transistor called LDMOS. LDMOS transistors could be soldered directly to an electrically grounded metal flange, thereby eliminating the need for BeO. The elimination of BeO reduced the cost of the package, as well as reduced the overall thermal resistance since most BeO packages contain a flange brazed beneath the BeO. LDMOS transistors ramped up in popularity by the end of the 1990’s. With the conversion from analog to digital cell phones in the early 2000’s LDMOS transistors dominated the market for amplifiers for cellular base stations.
Going forward, Materion is addressing other requirements of the RF transistor industry by manufacturing air cavity packages comprised of a ceramic frame brazed to a metal flange. The industry is demanding flanges with higher thermal conductivity and lower cost. Materion offers brazed ceramic packages with flanges made of CuW, CMC and CPC (Table 1). Various Materion locations are working with key customers to develop flanges made of copper, which will require an entirely new method to solder Si onto the flange due to the severe thermal expansion mismatch between Si and Cu."
but sure, nothing to see here.
except me not capitalizing a chem formula when i'm walking the dog
atleast now i know daily public exposure limit is for not using caps
me on the other hand, i can take 10X the exposure apparently, that helps because i've seen the non-hardened ceramic version of the stuff i was trying to warn OP about before i realized this is one of THOSE forum cultures where cred is more important than imfo
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