[sdiy] 45 vs. 90 degree pcb traces

Jay Schwichtenberg jschwich53 at comcast.net
Sat Feb 15 00:33:22 CET 2020

It was a photo process using high contrast film and photo-resist.

You'd actually use red, blue and black tape on a clear mylar sheet. We'd 
also always do our boards at 2X resolution too. Traces on both sides of 
the board were done with black tape, one side with red tape and the 
other side with blue tape. You'd take the layout somewhere where and 
they would make a 1X high contrast film (can't remember if negative or 
positive) for each side. They'd use red light to make the black and blue 
traces come out on the film for one side and blue light to make the red 
and black traces come out for the other side's film.

You'd then take the films and put them on a board with photo-resist, 
expose with UV light, etch and plate. Can't remember where in the 
process drilling and through-hole/via plating was done.

Jay S.

On 2/14/2020 3:14 PM, rsdio at audiobanshee.com wrote:
> Is there any documentation of the black versus red/blue Mylar tape 
> process?
> I’ve long assumed that the curved traces were hand-drawn with solder 
> resist pens, or some other, similar process that was mostly manual. I 
> also assumed that Mylar was cut with X-Acto blades. How would the 
> black “crepe” tape be cut? … and how is the width controlled?
> Despite the obvious pedantic tendencies, I actually believe it would 
> be historically important to document these old processes. It seems 
> that a number of computer history museums are gathering documentation 
> of these early events, and I’d like to see PCB design as a part of 
> that effort.
> Brian
> On Feb 14, 2020, at 11:39 AM, Harry <hbissell at wowway.com 
> <mailto:hbissell at wowway.com>> wrote:
>> Ok most of that is hooey! The curved traces were because the layouts 
>> were done with black "crepe" tape on Mylar. Curves are easy to do. 
>> That was superseded by red/blue Mylar tape which does not do curves. 
>> In  short, for audio frequencies there will be no difference. A good 
>> two layer or multilayer board would way outperform anything from the 
>> 1970's.
>> On Feb 14, 2020, at 2:10 PM, Harry <hbissell at wowway.com 
>> <mailto:hbissell at wowway.com>> wrote:
>>> On Feb 14, 2020, at 1:50 PM, Jimmy Moore <jamoore84 at gmail.com 
>>> <mailto:jamoore84 at gmail.com>> wrote:
>>>> This came up on the AH "behringer RD-6" thread:
>>>> >>Until the PCB traces are curvy (like on a 2600 or SEM) it's never 
>>>> going to sound authentic.   Electrons don't like corners.
>>>> I had picked up similar folk knowledge from my first engineering 
>>>> job working alongside techs, EE's, and designers.  I went looking 
>>>> for a more technical explanation on why this is the case, and it 
>>>> turns out it is NOT:
>>>> https://resources.altium.com/pcb-design-blog/pcb-routing-angle-myths-45-degree-angle-versus-90-degree-angle
>>>> (Notable exceptions being RF, high speed, or high voltage layouts)
>>>> This and another 
>>>> <https://electronics.stackexchange.com/questions/226582/pcb-90-degree-angles> resource 
>>>> debunk the pcb corner myth on EMI effects.
>>>> Is there any other tangible (audible) impact this decision could 
>>>> have for music electronics?  I think not, but I'd love to hear from 
>>>> other more experienced engineers on this (hopefully not tiresome) 
>>>> topic.
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