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DGZ80 TRIVIA - The PCB - Printable Version

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DGZ80 TRIVIA - The PCB - someone - 29-11-2020

The DGZ80 PCB was hand laid using Bishop Graphics at the usual 4X scale (ie. 2x width and 2x height) as a positive image.
(i.e. black = copper to, clear = no copper)
It is done at this size to make it easier for the PCB layout artist.
Various styles of prelaid IC footprints and tracing tape (which is essentially black masking tape) were used.

The accompanying Solder mask layout was also created at this scale. Only one was used to derive the component side and solder side solder masks).

An accompanying Drilling drawing was also created.  This symbolically shows the size of every hole on the PCB.

The Copper and Solder mask artwork is then photographically reduced to the desired size negatives which in turn are then replicated and laid out in arrays by the PCB manufacturer to form a large panel of images to best match the size of copper clad sheets used by the manufacturer.

The Drilling drawing is parsed by the PCB manufacturer to configure their drilling apparatus.  The apparatus could be just a manual fiducial alignment or an automated machine that accepts digital coordinates. It was common for the PCB manufacturer to use a combination of both methods so that a paper tape or computerised file could be created from the drilling drawing.

Depending upon the PCB, a physical dimension drawing was created to indicate to the PCB manufacturer the board outline and any slots to be milled.

Since the DGZ80 has a gold plated card edge connector, the appropriate information about was given to the PCB manufacturer.

This additional work is factored into the PCB manufacturer's quote.

Each PCB manufacturer uses their own preferred copper hole plating method. During the 1970's and 1980's the most common method was "Electroless" copper deposition.  The non etched but drilled PCB blanks are immersed into a chemical solution to allow the deposition of copper into the holes and onto the copper. This process has quite a few steps and is time consuming. There are many new and more reliable methods including an electroplating method that uses waterproof cured carbon ink within the holes because uses less steps and is much faster. Other methods include the use of Palladium.

The orientation of the ICs is not uniform but that is not necessarily a negative point.  By reorienting the ICs for minimum signal trace path improves signal integrity however it does make hand assembly more difficult and prone to error by requiring the assembler to ensure that the IC orientation is correct.

The 5V and GND voltage rail trace thicknesses vary greatly from being a essentially copper pour planes to 12mil traces to power some ICs.

Like most S100 boards of that era, the DGZ80 PCB is merely a "Join the Dots" artwork where no consideration to signal integrity was given.  In fact, the whole S100 bus paid no attention to signal integrity hence its issues and finnicky nature.  During that era many incorrect "Rules of Thumb" where used (and are still used today).  To address this unreliability, as an afterthought active termination was used.  It was usually available as an additional S100 card.  The DGZ80's layout exacerbated some signal integrity issues due to its long traces from some ICs (e.g. the Address buffers) to the S100 pins.  It is best to keep all S100 signals on S100 cards as short as possible meaning that the ICs are placed close to the S100 connector.

The power distribution network on the DGZ80 is woefully deficient thus causing unwanted ground bounce and power ripple and noise.
It is these deficiencies that made it easy for Steven Dompier to create the first sounds from S100 systems listening to the EM pollution on AM radios.  The EMI created by such computers prompted the FCC to create the necessary regulations to minimise it for safety's sake.


RE: DGZ80 TRIVIA - The PCB - ChickenMan - 29-11-2020

Thanks for that someone Smile

and we do have a copy of the pcb artwork of the solder side only in the repository also.  Reduced in size here

[attachment=112]


RE: DGZ80 TRIVIA - The PCB - someone - 29-11-2020

(29-11-2020, 11:30 AM)ChickenMan Wrote: Thanks for that someone Smile

and we do have a copy of the pcb artwork of the component side only in the repository also.  Reduced in size here

An excellent reference but that's the solder side!