Pat,

The reason I asked is because what I've seen over the years is that when rosin based fluxes or rosin cored solder wire is used the only time we've seen reliability issues (i.e., dendrite growth) is when the alcohol cleaning was used to remove the rosin residue and in many cases what happened was the cleaning wasn't complete and all that was removed was most of the rosin that was encapsulating the flux activators and once the rosin was removed the activators became mobile and would also be exposed to the humidity in the air.

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]


-----Original Message-----
From: Goodyear, Patrick [mailto:[log in to unmask]] 
Sent: Monday, March 12, 2012 1:51 PM
To: Wenger, George M.; TechNet E-Mail Forum
Subject: RE: [TN] Black substance

Based on the SOP of that time, most likely a Rosin core solder and cleaned with ethyl, or possibly mineral spirits.  
For repair we specify the use of Kester "44" 63/37 and ethyl to remove the flux.   We are not allowed to use no-cleans as it is an unanalyzed condition.    
Everything we do has to be exactly as original or an evaluated deviation (case by case basis) and signed off by a PE.  
All of the equipment is tested to provide certain known response characteristics for a given state based on environmental/accident conditions, and must be maintained in that state.   That is why a simple comparator circuit card with 10 components on it costs 10 grand, and I am tasked to evaluate and repair them. 

pat    

-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]] 
Sent: Monday, March 12, 2012 10:37 AM
To: TechNet E-Mail Forum; Goodyear, Patrick
Subject: RE: [TN] Black substance

Pat,

What cored solder wire or flux was used for the hand soldering operation and how were the boards cleaned?

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer Andrew Corporation - Wireless Network Solutions 40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Goodyear, Patrick
Sent: Monday, March 12, 2012 1:34 PM
To: [log in to unmask]
Subject: Re: [TN] Black substance

Thanks gang for the inputs it helped a lot.   Samples are being sent off for analysis.   Silver dendrites are my guess.

Inge, these are the boards for the instruments that monitor the power levels of a nuclear reactor they cannot be easily replaced, they are part of OEM, they were manufactured 1965 to around 1974 to the then state of the art soldered by hand.  They are single sided, single layer boards, without through plating, all of the runs appear to be plated with solder, there is no conformal coating.   I would expect the solder to be 60/40 and not 63/37 as I believe these were made before the time of 63/37 being widely used.    The boards were manufactured by Westinghouse, copper thickness is on the order of 5 thou. or thicker, all components are through hole.     Most of the "solid state" op amps are 1.5"x2" phenolic bricks made by Philbrick/Nexus (DL-21), all cards operate on +/- 25 vdc supplies.    Storage is in an environmental room with controlled humidity and temperature.     All of the hardware is either anodized, cad, or nickel plated, contacts are heavily gold plated Elco bifurcated contacts, most of the mounting posts are silver plated, most chassis components are aluminum with an anodized finish.

As a sidelight the nuclear program uses a lot of silver plating, this is good from an electronics standpoint but bad from a nuclear standpoint because if the silver is in an area of neutron bombardment it becomes VERY radioactive, contact readings can be on the order of several rem.

pat goodyear
control technician
Diablo Canyon Power Plant


________________________________
From: Inge Hernefjord [mailto:[log in to unmask]]
Sent: Thursday, March 08, 2012 11:15 PM
To: TechNet E-Mail Forum; Goodyear, Patrick
Subject: Re: [TN] Black substance

What is the purpose of your mixing with these antique boards?
My advice is that you perform a EDS or perhaps FTI R analysis of the fragments. Faster way than us guessing.
We know nothing about your products:
-manufacturer
-copper thickness
-number of layers
-finish
-size
-how were they stored?
-what environment?
etc.

Interesting forensic but little foggy

Inge




On 8 March 2012 19:39, Goodyear, Patrick <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Ok got a new one.    Found on the plated portion of a turret a black fuzz, also on the riveted backside and the plated portions of all of the lands outside the soldered areas.
It cleans right off with alcohol leaves no residue, is crystalline in structure and grows away from the metal has a coral like appearance.

I have attached pictures but Steve is off today so don't know who else can post.

Again a 40 year old board.

Any ideas????

Pat

.


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