I've seen far worse than that! Outstanding in my memory are a number of 
boards comprising an NC control, manufactured by a large well-known 
German company, used in the controller for a precision grinder. This was 
in about 1972 or 73 and the boards were single Euro cards, PTH with, of 
course, conventional components. This was in the days before solder 
masks were common.

The assemblies were wave soldered, using a thick layer of halogen free 
flux, activated by a carboxylic acid. This was almost a sine qua non 
with this particular manufacturer, who promoted this technique into DIN 
standards.

The solder side was obviously coated with a thick layer of solder, 
mostly because the solderability was doubtful. The conductors on the 
component side were in bare copper. On the faulty boards, the latter was 
totally corroded away in many places, but particularly round the plated 
through holes where the molten flux had penetrated upwards. Remember 
that this was not a grand public application, but a supposedly highly 
professional bit of electronics.

Where did the error lie? In my opinion, the electronics for a grinding 
machine should never have been put into an ordinary cabinet with 
ventilation louvres, but into a hermetic enclosure. Why? Because 
grinding machines require lubrication and that lubrication forms a mist 
which pervades the workshop, including into the electronics. Worse, the 
lubrication consists of a water-soluble oil which may be 80 or 90% 
water. The electronics were therefore subjected to a perpetual water 
mist, with the results that may be expected.

I don't know whether the choice of housing of the electronics was 
offered by the NC controller manufacturer or that of the grinding 
machine manufacturer. Whatever, it was a fatal and costly mistake. I was 
consulted to determine the cause of the corrosion, although anyone who 
is blind in one eye and couldn't see with the other would have been able 
to see that straight away. Unfortunately, it proved impossible to house 
the electronics in a hermetic box, because the servo motor controllers 
ran very hot and needed that heat evacuated by good ventilation. I 
compromised and recommended a box which was minimally ventilated but 
purged with compressed air impinging on the servo motor controllers. 
This provided a slight positive pressure, sufficient to keep the mist 
from entering the box. I don't consider this was ideal but it seemed to 
do the trick.

Brian

On 17/01/2011 02:01, Steve Gregory wrote:
> Well I finally got your photos Inge! Don't have a clue why it took so
> long, and don't know why it took multiple tries to get your photos. Did
> you try both my work and personal email addresses? Very strange!
>
> Anyway, here are your photos. I have never seen such a pile of shit! I
> understand the true meaning of IPC Class-I electronics now. All my
> instructors have emphasized during certification classes that Class-I
> electronics only have to work once. There's no requirement for them to
> work beyond the first time they are powered up. But I think what you are
> showing us pushes the limit of how terribly something can be made and
> still be called a Class-I assembly!
>
>> From your pictures it looks this board was assembled (if you can
>> called it
> that), and then put into it's plastic case with a very corrosive flux
> left on the board. They probably had to use a very active flux to get
> the solder to wet to anything on that crap!
>
> Here's the links to your photos. I must caution everyone not to click on
> these links if you have a queasy stomach. What you are about to see is
> pretty stomach churning!
>
> http://stevezeva.homestead.com/DSC_8741b.jpg
>
> http://stevezeva.homestead.com/DSC_8743.jpg
>
> http://stevezeva.homestead.com/Kopia_av_DSC_8744.jpg
>
> http://stevezeva.homestead.com/Kopia_av_DSC_8745.jpg
>
> http://stevezeva.homestead.com/Kopia_av_DSC_8746.jpg
>
> Steve
>
> -----Original Message----- From: Inge
> Sent: Thursday, January 13, 2011 6:06 PM
> To: [log in to unmask]
> Subject: [TN] a different Friday quiz
>
> I bought a digital temperature equipment, consisting of a inhouse table
> unit
> and a outdoors unit. Cost = 25 USD. Cheap? Yes. But let's have a look on
> inside after the problem, which started just a few weeks. You can read the
> inside temperature, clock works, date works, and you can use the alarm and
> shift between the four channels, but the receiver does not take in the
> signals from the little sender on the wall any more. I dismantled the box
> and marvelled when I saw the shit I payed for. It's a wonder that there are
> any functions working at all! Now, what caused the dead receiver was a flow
> of iron from one screw (upper left corner ) . There is a bridge of
> corrosion products (brown and green) from the screw to the thermistor (RT)
> continuing to the rest of the circuitry. When I washed the card and dried
> it, the reciever worked again,
>
> Now, folks, here comes a question for the sharp TNetters:
>
> "How can the screw be so rusty and deliver iron ions when it's not
> connected
> to anything? It's just torqued into the plastic body. The other screws are
> identical, but have not been involved in anything. "
>
> The box has been on the kitchen table and has not been exposed to humidity
> or any else abnormal condition.
>
> The two 1.5 V batteries are removed on the pics.
>
> Hope the gregorian Steve will help me with the photos.
>
> /Inge
>
>
>
>
>
>
>
>
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