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Subject: Re: Surface finish for space

Date: 05/02/00 at 8:24 AM
Posted by: James Jackson
E-mail: JOJ@Texas.net
Message Posted:

In Reply to: Surface finish for space posted by Brendon Parise on 05/01/00 at 10:32 PM:

Hello Brendon,

In a previous life, I was required to do layouts for space flight.

Standards you should be aware of are:

The spec that I used way back when, was NASA NHB 5300.4(3I), but NASA has cancelled this spec., and has called out the requirements in IPC-6011, Class 3 and IPC-6012 instead.

NASA uses NAS 5300.4 (3J-1) for conformal coating and staking.

NHB 5300.4 (3K) was cancelled, and NASA now calls out IPC-2221 and IPC-2222.

There are several other issues that you will need to address dealing with outgassing, temperature, etc.

The boards that I designed had no soldermask, but silkscreen was allowed as it was a special formulation ink that did not outgas (or fell within the NASA limits for outgassing).

The board material was not FR-4, but Polyimide, also due to outgassing issues... as well as elevated temperature issues.

You will need to spend some time creating 'coupons' for cross-sectional testing. These get placed along the outside edges of the P.C. board, and will be used to verify the integrity of the PCB.

The boards also had parts on them that got hot. They needed special 'Thermal Vias' that conducted the heat from the parts to a special inner copper layers that were something like 4oz or 8oz copper. This layer was electrically bolted to the chassis of the enclosure where the heat was dissipated.

The boards worked very well, but required a thermal engineer to design the thermal aspects of this design.

If you have any devices that are tall, they will ned to be secured or staked to the board per the NASA spec.

The PCB fabricator that you use will also need to be qualified to produce NASA/MIL-Spec flight boards.

I also seem to remember lots of documentation for everything. This requirement got worse after the Challenger incident.

Well, at least that's the way I remember it. Things may have changed a bit since I last did a NASA board.

Have fun,

James Jackson
Oztronics


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