Electronic soldering for spacecrafts 1

[AeroAd]

Hi,

Do someone know if there are standards or norms (soldering technics, kind of solders...) on electronic soldering for spacecraft applications.

Thanks.

Adam
Québec, Can

 

[Jick]

Try NASA-STD-8739.3 -- Soldered Electrical Connections. As for materials selection, MSFC-HDBK-527 -- Materials Selection List for Space Flight Hardware, might be of help.

sean

 

[Heckler]

AeroAd,

Here are some q&a from a meeting I attended.

1. What is the best way to shock-mount the printed circuit boards?

Shock mounting is not really necessary if the PCB is properly designed and large parts are secured to the board with adhesive. Be certain to make the board stiff enough so it cannot ‘oil can’.

2. What is the best axis to orient printed circuit boards on with respect the launch direction?

The axis is generally not critical especially with small boards.

3. What material should be used as a conformal coating on the PCBs?

Conformal coating is generally not recommended except as an electrical insulator to prevent shorts in the event a piece of loose conductive material contacts the board. Conformal coating will not prevent outgassing.

4. How well do through-hole PCBs hold up as compared to surface-mount?

Through-hole PCBs have been the standard until recently when surface mount technology was developed. Both technologies have their own characteristic points of failure but if designed correctly, both are acceptable for use in satellites.

5. What is most likely to be damaged on a surface mount PCB during launch?

Components with insufficient pad area or poor mounting are likely to fly off the board. Use a drop of epoxy beneath components to mechanically secure them. Make pads as large as possible. Testing using a shake table is mandatory.

6. Are there certain types of surface mount components that are known to have problems surviving a launch?

None in particular, provided that the pads are large enough and they are properly secured to the board.

7. Should we be concerned about a failure of the actual copper traces on the PCB and, if so, what precautions should be taken to minimize a failure
(i.e., trace width, board thickness, copper weight, number of layers)?

Thickness: >0.062”
Trace Width >10mil
Trace Isolation >10mil
Power and ground planes are mandatory to prevent ground bounce and should be the two center layers. Have one signal plane for horizontal traces and another for vertical on the outside layers. Do not use blind vias, it prohibits access to test points. Minimize trace lengths by intelligently placing components. Do not autoroute PCBs.
Leave >20mil space between edge of board and any copper to prevent shorts. Avoid placing traces beneath components.
Make traces as wide as possible.

8. Are there guidelines for determining acceptable PCB specifications?

Refer to IPC275, MIL -STD-275, and MILP55110. I am currently attempting to obtain these specs.

 

[HeavyWater]

All MIL specs are free to access at the ASSIST web page created by the Department of Defense.

http://assist1.daps.dla.mil/online/start/