Re: Real 82S100 in C64

On 02.09.2012 21:56, Gerrit Heitsch wrote:
> On 09/02/2012 09:07 PM, silverdr@wfmh.org.pl wrote:
>> Like most HK boards, with excessive solder flowing under ground planes
>> and traces, making it more difficult to desolder things, with solder mask
>> peeling off, etc. This is how most of the boards look like. Japan boards
>> were of top quality. Clean, flat soldered, no peelings of anything.
>
> Hm, I know the kind of board you are refering to. They usually have a light
> green solder mask while the others do have all kinds of other colors. But
> to me this looks like only one specific maker and I only have one of their
> boards, all others in my collection are of good quality and, from what's
> printed on them, from all kinds of makers. The sticker on the expansion
> port bracket always says 'HKC' though, which I read as 'Hong Kong'.

I also know that kind of boards. I wouldn't say the PCBs are low quality, 
they were just made with a different process which is more sensitive to 
wrong temperature in wave soldering or something like that.

The difference is in the surface of the traces prior to applying the solder 
mask. The older ("better") boards have blank copper traces which are then 
covered by the stop mask. There is no tin, lead/tin or solder layer between 
the copper traces and the stop mask! Nowadays, this is the preferred 
process because it saves you money if the tin layer is only present on 
exposed contact areas. During wave soldering, it is almost impossible for 
the wave solder to get between copper and solder mask.

The other boards have a tin or tin/lead layer applied to the copper before 
applying the solder mask. During wave solder, if the temperature is too 
high, or contact time too long, the tin layer will melt and excess solder 
can flow into this layer, giving the effect we all know.

I think there is also an advantage of the tinned boards. If you have a 
leaking capacitor, the alkaline electrolyte will attack the solder mask and 
the copper traces readily. The tin layer will protect the copper trace so 
there will be no or less attack to the copper.

Nicolas

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