SATPC0040394 Tab 04 4 SOW.pdf

Statement of work for the brazing of silicon nitride to compatible metal for high temperature environment

• The vendor shall conduct the following:

o investigate suitability of sintered silicon nitride (Si3N4) for packaging NASA SiC sensors for

1000 °C operation.

o provide NASA-GRC (1.0 x 1.0 x 0.040) inch3 high purity Si3N4 substrates (Qty=4) for electrical o characterization by NASA.

o provide elemental analysis of the Si3N4 by Glow Discharge Mass Spectrometry (GD-MS) o investigate the brazeability of Si3N4 dummy headers (Qty=15) to a metal tube

(including Inconel 718) that is oxidation resistant and thermos-mechanically compatible with the Si3N4.

o apply electroplating and braze joining technique between the metal tube and the Si3N4 dummy o headers. The Si3N4 dummy headers will be Mo-Mn thick film metallized and Ni plated for brazing to Inconel 718 tube.

o ensure that the braze joint is impervious to oxidation at 1000°C in atmosphere for a minimum of 1 hour.

• Metallized and Ni plated Si3N4 headers shall be brazed to the Inconel 718 metal tubes using BAu-

3 braze

• alloy.

• Brazed joints shall be pressure tested using He-water immersion method.

• The joints shall be cross-sectioned and examined under light microscope for voids, cracks and other

• potential defects.

• Five (5) SiC pressure sensors shall be packaged based on the specification below.

• The components to be used for packaging the silicon carbide pressure sensors shall

• withstand pressure of up to 500 psi and temperature up to 900 oC for a minimum of one

• hour at NASA-GRC.

• The preferred packaging architecture shall be based on the MEMS Direct Chip Attach

• concept similar to the one referenced in Fig. 20 of US patent 7,518,234.

• The package shall be a 7-through-hole via with central reference cavity fabricated in the

• ST-200 aluminum nitride (AlN) header that is closest CTE matched to the SiC sensor

• material.

• The diameter of the AlN header shall be 0.278” and the shoulder diameter to be

• reduced from the current 0.2465”. New diameter to be determined.

• The AlN header that houses the SiC sensor shall be brazed to Kovar tube with OD=0.279”

• and ID to be reduced from current 0.251”.

• Kovar tube or any complementary low CTE material with low oxidization rate that would

• survive a minimum of 1 hour in air at 900 ℃.

• The brazing material (NiCuSil-3) to braze the AlN header to the Kovar tube shall be nonoxidizing https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.thermofisher.com/us/en/home/industrial/mass-spectrometry/glow-discharge-mass-spectrometry-gd-ms.html&ved=2ahUKEwjI-4LC9sKSAxW7K1kFHc-fBRkQFnoECA8QAQ&usg=AOvVaw3EUv_12boZqPS6KK-0OpKP https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.thermofisher.com/us/en/home/industrial/mass-spectrometry/glow-discharge-mass-spectrometry-gd-ms.html&ved=2ahUKEwjI-4LC9sKSAxW7K1kFHc-fBRkQFnoECA8QAQ&usg=AOvVaw3EUv_12boZqPS6KK-0OpKP

• or have low oxidation rate to survive a minimum of 1 hour in air at 900 ℃.

• The brazed joint between Kovar tube and the AlN header shall be leak free during use

• for a minimum of 1 hour in air at 900 ℃. Leak rate lower than 6x10-7 would be

• acceptable.

• The leakage current between pins (Au or Pt) and the AlN header carrier substrate shall

• be no more than 0.1 μA (10 Vdc) at 900 oC at NASA-GRC.

• Pt wire (0.007”) shall be used to paste and cure to connect to sensor pads.

• Alumina tube to sheath the Pt wires.

• Each packaged sensor shall be tested at room temperature prior to shipment