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December 2015

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From:
"Upton, Shawn" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Upton, Shawn
Date:
Tue, 1 Dec 2015 20:22:57 +0000
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I'm curious about the solderjoint itself.  Looks like poor wetting, but it looks like what they show as cracking looks more like a lifted land.  Also, what is the discoloration on the green trace running away from the land?  Reminds me of a board that I saw where the copper was damaged by battery acid.  Is that just an artifact from the conformal coating being removed during inspection?

The more I look at it, the more it looks like the crack goes all the way around the joint though, can see a faint line most of the way down the fillet.

The DB-looking connector is corroded, but across from that it looks like a transformer got attacked by the seawater also--so not fully conformally coated?  I could see wear and tear on the DB, but I would have thought the whole board would be conformally coated.  Speaking of which, I wonder if that is where the cracks live, under that transformer-looking thing.  All the other components look like they would have "give" for thermal expansion/contraction.  Well, maybe not the TO cans I guess, but the photo makes it look like that particular crack was relatively away from everything else.  But if the iron core was being attacked by seawater, well, maybe that is where the rust color on the cracked solderjoint is from.

That, or maybe it's under the relay--the lead itself is very rounded, making think it's a relay pin.  Which would sit flush on the board, and perhaps yank.  Certainly "clicks" on accuation.  But then the rust would come from...? the iron core inside the relay?

Anyhow, I looked through the report, and while it's huge it appears it is the typical cascade of failures--not one thing but rather several things went wrong, each compounding the prior.

Shawn Upton

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, December 01, 2015 3:15 PM
To: [log in to unmask]
Subject: Re: [TN] Airbus crash pinned (in part) on solder joint failures

I did a little more digging on the Esterline web page and looked at the photo a little closer, and that relay doesn't fall into the ones that have the space restrictions. This is the relay that is on that board:

http://us.leachint.fr/aerospace/f250/

Steve

On Tue, Dec 1, 2015 at 12:41 PM, Steve Gregory <[log in to unmask]> wrote:

> There is something that I noticed on the photo of the electronic module.
> The board on the left that has the four Leach relays looks like there 
> was a violation of a documented recommendation by Leach of the 
> positioning of the relays next to each other. The document states that 
> the permanent magnet inside the relay could affect the performance of 
> another relay next to it if it is oriented in the same direction and not separated by at least 1/8":
>
> http://www.leachintl2.com/english/english1/vol0/properties/N023eng.htm
>
> It looks to me like all four are oriented the same way and looks to me 
> like they're closer than 1/8" = .125" = 3.175mm to each other. What do 
> you think?
>
> Steve
>
> On Tue, Dec 1, 2015 at 11:37 AM, Stadem, Richard D. < 
> [log in to unmask]> wrote:
>
>> Agreed. There was no redundancy here, nor was there an effective 
>> default condition.
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne Oosterhof
>> Sent: Tuesday, December 01, 2015 11:35 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Airbus crash pinned (in part) on solder joint 
>> failures
>>
>> Figure 35: Electronic Module of RTLU
>>
>> Not much of a failure to cause the loss of life and an aircraft!
>>
>> Conclusion: End-use of a board module dictates extreme level of 
>> attention to design and testing protocols.
>>
>> Ahne.
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Buetow
>> Sent: Tuesday, December 1, 2015 6:28 AM
>> To: [log in to unmask]
>> Subject: [TN] Airbus crash pinned (in part) on solder joint failures
>>
>> Here's the report: 
>> http://kemhubri.dephub.go.id/knkt/ntsc_home/ntsc.htm
>>
>>
>>
>> Discussion of the electrical short and cracked solder joint begins on 
>> page 104.
>>
>>
>>
>>
>>
>> Best,
>>
>>
>>
>> Mike
>>
>>
>>
>> Mike Buetow
>>
>> PCD&F/Circuits Assembly
>>
>> w/m: 617-327-4702
>>
>> @mikebuetow
>>
>>
>>
>> The 2015 CIRCUITS ASSEMBLY *Directory of EMS Companies:* 
>> circuitsassembly.com/dems
>>
>>
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