Manufacturing Server Sky

Devices and materials

A lot can be done on a very thin planar surface. Other things cannot be done easily. Here are some common electronic devices:

Thin Planar	Non-planar
Printed circuit laminates (ultrathin)	Connectors
Resistors	cooling fins
Planar Capacitors	Wound foil capacitors
pixel sensor arrays	lenses
liquid crystal light modulators	LEDs (?)
Striplines	Coax
Microwave-frequency inductors	Low frequency inductors and transformers
surface acoustic wave (SAW) resonators	crystals
beam lead interconnect	wirebonds and solderbumps

Silicon is the construction material of choice - the solar cell is made of silicon, and the processors and memory are also. Here are some relevant properties of silicon, SiO2 glass, gallium arsenide, copper, aluminum, silver, gold, tantalum, indium tin oxide, kovar, invar, low expansion borosilicate glass, and pyrolytic graphite, which will make up 99.9% of the weight of a server-sat:

property	Si	SiO2	Si3N4	GaAs	Cu	Al	Ag	Au	Ta	ITO	Kovar	Invar	BSiO2	PyroC
Density g/cm^3	2.33	2.65	3.20	5.32	8.96	2.7	10.5	19.3	16.7	6.43	7.85	8.05	2.23	2.25
Coeff. of Thermal Expansion 10-6/K	2.6	0.5	3.2	5.7	16.5	23.1	18.9	14.2	6.3	10?	5.3	1.3	3.25	4.3
Heat Capacity J/g-K	0.71	0.74	0.71	0.33	0.38	0.90	0.24	0.13	0.14	-	0.44	0.51	0.75	0.72
Heat Capacity MJ/m³-K	1.65	1.96	2.27	1.76	3.40	2.43	2.47	2.49	2.34	-	3.45	4.11	1.67	1.62
Thermal Conductivity W/m-K	149	1	30	55	401	237	430	320	58	-	17.3	10.1	1.1	1950
Specific thermal conductivity	64	0.4	9.4	10	45	88	41	16	3.5	-	2.5	12	0.7	870
Thermal Diffusivity mm²/s	90	0.5	13	31	118	98	174	129	25	-	5	2.5	0.3	1200
Youngs Modulus GPa	150	73	260	86	110	70	83	78	186	116	140	148	63	4.8
speed of sound km/s	8.0	5.2	9.0	4.0	3.5	5.1	2.8	2.0	3.3	4.2	4.2	4.3	5.3	1.5
Tensile Strength MPa	7000	50	70	57	210	40	170	100	200	120	270	680	35	-
Atomic Weight (avg/atom)	28	20	20	72	64	27	108	197	181	57	57	56	19	6
Resistivity nano-ohm-m	-	-	-	-	17	27	16	22	131	2200	490	820	-	14000
Dielectric Constant	11.8	3.9	7.5	12.9	-	-	-	-	-	-	-	-	4.6	-

Data mostly from wikipedia and various places online. See also Matweb the material properties website, B.Y.U. CTE table. Tensile strength untrustworthy, and many parameters are anisotropic. Use only for rough estimates.

The vast bulk of the material , and the largest pieces of of the server-sat, will be silicon. Since the server-sat undergoes wide temperature changes when it passes in and out of shadow, or undegoes thermal annealing, it will be more survivable if the non-silicon portions are made of composite materials that match silicon's 2.6E-6/Kelvin coefficient of thermal expansion (CTE). For example, Zicar Ceramics SALI-2 (search on Matweb]] is a mixture of 80% alumina, 20% silica with a a CTE of 6.2E-6 . Alumina, combined in different proportions with silica ( SiO2 ) , might be nicely matched to silicon.

Server sats will also need transparent materials and conductors that closely match silicon. The metals have very high CTEs, while SiO2 has a very low CTE, so slotted metal wires with SiO2 in the gaps is one way to make a "material" that is both conductive and has the same CTE as silicon.