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Project and File Names

  • Project: [SatelliteName_SubsystemAcronym_BoardName_REV]
  • Top level Schematic connection sheet: [SatelliteName_SubsystemAcronym_BoardName_REV]
  • Subsheets: sheet[n]
  • Subsystem Documentation: [SatelliteName_SubsystemAcronym_BoardName_REV] [DataSheet/interface/summary/etc].pdf
  • Release Checklists: [yyyy-mm-dd] [SatelliteName_SubsystemAcronym_BoardName_REV] [FileName].pdf

Libraries

Please see the following YouTube videos for how to install and use our libraries.

Schematics

Consistent Use of Parameters, designators, and comments throughout all of our designs will allow for easier reuse of librarys, generation of bill of materials, and general filtering and searching for components when using altium.

**Style**

All Schematics shall use a single top level connections sheet named using the [SatelliteName_SubsystemAcronym_BoardName_REV] format with all the actual schematics in sub sheets numbered. Please set Ports to there expected direction (In/Out/Bidirectional) this helps detect errors in the schematic. Always display net names on power objects, Remember that Altium is case sensitive (VCC is NOT the same as Vcc as a net) always displaying the net name can help prevent errors caused by this. Please use the signal ground symbol (triangle) not the power ground symbol (three horizontal lines) for normal digital ground connections. All I2C peripherals must have a comment near the symbol with its address (include all timing and comms parameters required to setup communication with the chip). All SPI peripherals must have a comment near their chip select with the port and pin number as it appears to the firmware (include all timing and comms parameters required to setup communication with the chip).

**Component Parameters**

  1. Description (just copy the Digikey one, they are good)
  2. Supplier (generally Digi key or Mouser)
  3. Supplier Part Number (Makes ordering easy, we can just upload the BOM output by Altium to Digikey and press order if you do this correctly)
  4. Manufacturer (Good to have so we can figure out what the Manufacturer part number is)
  5. Manufacturer Part Number (For if Digikey/ the previous supplier we where getting this part from is out we can then find it from another supplier)
  6. Last Modified Date, yyyy-mm-dd format (This lets us track back changes and know who to contact to get an explanation of them)
  7. Last Modified By (This lets us track back changes and know who to contact to get an explanation of them)

**Component Designators**

? indicates number, by setting up your schematic symbols to default to the correct character and a ? it allows you to use the automatic annotation tools in Altium as well as filter and search for components in a consistent way across all of our projects. As per IEEE 200-1975/ANSI Y32.16-1975:

Designator Component Type
A? Separable assembly or sub-assembly (e.g. printed circuit assembly)
AT? Attenuator or isolator
BR? Bridge rectifier
BT? Battery
C? Capacitor
CN? Capacitor network
D? Diode (including Zeners, thyristors and LEDs)
DL? Delay line
DS? Display
F? Fuse
FB? Ferrite bead
FD? Fiducial
FL? Filter
G? Generator
GN? General network
H? Hardware
HY? circulator or directional coupler
J? Jack (least-movable connector of a connector pair) connector (connector may have “male” pin contacts and/or “female” socket contacts)
JP? Link (Jumper)
K? Relay or contactor
L? Inductor or coil or ferrite bead
LS? Loudspeaker or buzzer
M? Motor
MK? Microphone
MP? Mechanical part (including screws and fasteners)
P? Plug (most-movable connector of a connector pair) connector (connector may have “male” pin contacts and/or “female” socket contacts)
PS? Power supply
Q? Transistor (all types)
R? Resistor
RN? Resistor network
RT? Thermistor
RV? Varistor
S? Switch (all types, including push-buttons)
T? Transformer
TC? Thermocouple
TUN? Tuner
TP? Test point
U? Inseparable assembly (e.g., integrated circuit)
V? Vacuum tube
VR? Variable resistor (potentiometer or rheostat)
X? Socket connector for another item not P or J, paired with the letter symbol for that item (XV for vacuum tube socket, XF for fuse holder, XA for printed circuit assembly connector, XU for integrated circuit connector, XDS for light socket, etc.)
Y? Crystal or Electronic oscillator
Z? Zener diode

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**Component Comments**

  • Capacitors: try and keep values in uF or pF, include F at the end of the value
  • Resistors: Do not use R just the value ie 100k (100 thousand ohm) 1m (1 milli ohm) 1M (1 mega ohm) 100 (100 ohm)
  • Inductors: include H at the end of the value
  • Integrated Circuits: Manufacturers part number
  • Connectors: Manufacturers part number
  • Other: Manufacturers part number

PCB Layers

Copper

  • Top layer
  • Mid layer 1 (Not always used)
  • Mid layer 2 (Not always used)
  • Mid layer 3 (Not always used)
  • Mid layer 4 (Not always used)
  • Bottom layer

Solder Mask

  • Top Solder (Top solder mask)
  • Bottom Solder (Bottom solder mask)

Solder Paste

  • Top Paste (Top Solder Paste mask)
  • Bottom Paste (Bottom Paste mask)

Mechanical

  1. Board Outline
  2. Board Labels and information
  3. Top Layer assembly drawing
  4. Bottom Layer assembly drawing
  5. Top layer dimensions and mechanical information
  6. Bottom layer dimensions and mechanical information
  7. Unused
  8. Unused
  9. Unused
  10. Unused
  11. Unused
  12. Unused
  13. 3D Information
  14. Unused
  15. Component keep out Information

Other

  • Keepout: Duplicate board outline, this is needed for using oshpark

Routing Guidlines

  • When routing all traces, determine maximum current and set trace width to max current * 1.2 for a small safety factor using the internal layer calculation from pcb trace width calculator. The factor of safety accounts for the fact that on external layers we are not just missing air but also the FR4 that allows thermal heat transfer in all directions on the mid layers.
  • When routing RF traces, using impedance-controlled routing in Altium.
    • This requires that you specify your stackup first.
    • Remember, power planes act as ground planes for RF signals.
    • For extremely critical RF signals (eg: Ka microwave band) you may want to use stripline (internal trace between two planes) rather than microstrip (external trace over one plane). This is not required on ECOSat-2 but may be necessary on a future satellite.
  • Vcc Traces MUST connect to a chip through a decoupling capacitor, (i.e. the Vcc trace must connect first to the decoupling capacitor then from the decoupling capacitor a separate trace should lead to the Vcc pin of the IC)
  • Calculate load capacitors for XTALs by taking into account the parasitic capacitance of the PCB in pins, take a read through https://www.adafruit.com/blog/2012/01/24/choosing-the-right-crystal-and-caps-for-your-design/
  • When laying out XTALs keep in mind
    • Avoid vias and right angle corners for signal traces
    • Keep the signal traces neat and as close to the same length as possible
    • Try and use ground planes on adjacent layers
    • A ground guard trace (separated from the ground pour) around the crystal should be used, while this is not really necessary with our slow crystals it is good practice
  • Do not allow for acute angles in copper (sub 90 degree) this adds a place for acid to collect and makes the board harder to manufacture without errors.
  • Try and keep vias at least 16mil hole 28mil pad or larger.
  • Keep components at least 40mil (1mm) from the edge of the board
  • System critical traces should be redundant
  • Keep components at least 75-100mil from the pins of the bus connector on the bottom layer
  • Keep components at least 40mil from the plastic housing of the bus connector on the top layer
  • Attempt to keep a clean ground connection under all medium to high speed signals to reduce EMI emission
  • Separate grounds to isolate sensitive electronics and sensors from noisy digital grounds or from power grounds
  • Consider adding RF cans over processors and memory, to add additional shielding and delay TID death. Only do this if you have extra room and the addition of it will not impeded the routing or placement of components for the intended purpose of the system
  • Consider adding SMD test points with available room as long as it does not adversely effect the grounding of the system (i.e. does not significantly cut ground plans or connections)
  • Do not allow for acute angles in copper layers (corners smaller than 90 degrees) this becomes a place for acid to pool during manufacturing and can reduce the reliability of the area by eating away under the copper.
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