[eagle] Re: CAN-Do noise abatement plan and questions

Chuck Green greencl at mindspring.com
Thu Jun 14 10:03:59 PDT 2007

I would strongly suggest that after you have a prototype unit working 
enough that you are convinced you have chosen the right parts, it be 
radiation tested.  Hopefully your PCB is of a size that will fit in 
Stacey's chamber.  This should be a consideration when sizing any 
project's PCB.  If it is not, you may have to produce a PCB sized for 
the purpose, not for flight.  That's why the IHU is 100mm wide; Stacey's 
chamber had a 4" limit.  He has a new, larger, chamber now (I don't know 
it's size).

SOS technology parts are inherently rad-hard.  Of course, "rad-hard" is 
a relative term.  The manufacturer may specify the tolerance since it is 
something they can feature.  If they don't publicly state it, they may 
still know what it is and you might be able to talk to them and pry it 
out of them.  We had some rad-hard memory ICs for the IHU in P3D but we 
still shielded them - probably unnecessary. 


John B. Stephensen wrote:
> OK. The PIC MCU that I'm considering should be safe. It's rated for 40 
> years data retention in an automotive temperature range. Most parts 
> guarantee only 10 year data retention or say nothing on the data sheet.
> The PLLs are in J-lead PLCC packages, but they are silicon on sapphire 
> so they may not need shielding.
> 73,
> John
> ----- Original Message ----- From: "Chuck Green" <greencl at mindspring.com>
> To: "John B. Stephensen" <kd6ozh at comcast.net>
> Cc: "Robert McGwier" <rwmcgwier at gmail.com>; "Bill Ress" 
> <bill at hsmicrowave.com>; <eagle at amsat.org>
> Sent: Thursday, June 14, 2007 15:55 UTC
> Subject: Re: [eagle] Re: CAN-Do noise abatement plan and questions
>> John,
>> Yes, the CAN-Do! s were radiation tested and did very well.  That was 
>> one of the first things done.  It was a special PCB that had some 
>> alternate parts on it for us to choose from for the final version.  
>> The test was run without the Tantalum shields.  The Tantalum shields 
>> reduce the dose rate so we are very comfortable with the device for 
>> the mission.  We probably didn't need to shield everything like we 
>> did but it's easier to do that after testing the total device rather 
>> than try to figure out what each component can tolerate.  Our police 
>> is to shield any device that contains an FET, top and bottom.  I took 
>> this into consideration when designing the layout for this and the 
>> IHU so there are ICs of similar size on opposite sides of the PCB as 
>> much as possible so that the top shield on one provides bottom 
>> shielding for the other.  It's not possible to shield the bottom of 
>> an SMD IC except to put the shield on the other side of the PCB 
>> anyway (J-lead SMDs are an exception to this but we don't use very 
>> many of them).  Tantalum does an outstanding job of shielding.  
>> Sometime when I see you, ask me to tell you about the time I forgot I 
>> had a piece about 6" square in my brief-case when going through 
>> airport security.
>> Chuck
>> John B. Stephensen wrote:
>>> Bob:
>>> Were they tested sufficiently for radiation resistance? I'm assuming 
>>> that the tantalum was used to add radiation shielding for things 
>>> like flash memory on the MCU. Mirek's receiver also uses flash 
>>> memory to store the frequency. The PLLs used in the existing 70 cm 
>>> receiver can be purchased in a pin-compatible rad-hard version. 
>>> However, the frequency has to be stored in flash memory. PIC MCUs 
>>> hold data for 40 years on earth but space is a harsher environment.
>>> We have the option of buying PLLs (with more pins) that can be 
>>> hard-wired to a particular frequency. These PLLs are much more 
>>> expensive and have longer lead times as they are space rated.
>>> 73,
>>> John
>>> KD6OZH
>>> ----- Original Message ----- From: "Robert McGwier" 
>>> <rwmcgwier at gmail.com>
>>> To: "Bill Ress" <bill at hsmicrowave.com>
>>> Cc: <eagle at amsat.org>
>>> Sent: Thursday, June 14, 2007 10:46 UTC
>>> Subject: [eagle] Re: CAN-Do noise abatement plan and questions
>>>> That they were not sufficiently tested by anyone who was to use 
>>>> them to
>>>> build flight units.  This consumed tantalum slides, and lots of 
>>>> effort.
>>>> Stephen got essentially zero feedback from the engineering test 
>>>> units he
>>>> sent.  This noise issue could have easily been found.  They have 
>>>> had the
>>>> engineering units for a LONG time.
>>>> Bob
>>>> Bill Ress wrote:
>>>>> Hi Bob,
>>>>> Just curious - what were the "objections?"
>>>>> Regards...Bill - N6GHz
>>>>> Robert McGwier wrote:
>>>>>> The Germans demanded their flight modules over the objections of the
>>>>>> designers and manufacturers so they are on their own with the
>>>>>> consequences.
>>>> -- 
>>>> AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
>>>> "If you're going to be crazy, you have to get paid for it or
>>>> else you're going to be locked up." Hunter S. Thompson
>>>> _______________________________________________
>>>> Via the Eagle mailing list courtesy of AMSAT-NA
>>>> Eagle at amsat.org
>>>> http://amsat.org/mailman/listinfo/eagle
>>> _______________________________________________
>>> Via the Eagle mailing list courtesy of AMSAT-NA
>>> Eagle at amsat.org
>>> http://amsat.org/mailman/listinfo/eagle

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