Why Are There No Right Angle Traces?

[Tom Woodrow]

Had to do that on a 6-layer board once.

Hand taping was so much fun. Actually I enjoyed
it most of the time. I even thought in 4x for a
long while after I laid out my last tapeup PCB.

Tom Woodrow
www.dacworks.com

 

[Frank Miles]

In article <3F025B7F.2040209@comcast.net>,
Tom Woodrow <tomwoodrow@comcast.net> wrote:

This an old thread but I can't resist adding my 2 cents.

1. Don't know about when they did PCB artwork with Pen and Ink, but when
we started using tape to layout PCBs (for me 1967), the tape would roll
up at 90 degree corners. Bas thing for storing taped artworks.

[snip]

Ah, but at least with tape you can bevel those nasty right-angle corners,
virtually eliminating the minor TDR glitch.

-frank
--

 

[John Larkin]

On Wed, 02 Jul 2003 16:34:28 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Wed, 02 Jul 2003 10:14:03 -0700, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:


What a pain. I still like to draw schematics with a Berol Turquoise on
vellum (then I let the kids CAD it for me) but I'll never get
nostalgic about taping boards. I remember two, three weeks of leaning
over a hot light table, holding my breath every time I had to lay a
line between two IC pads. I remember discovering that we'd have to
move a whole section left 150 mils. I love PADS... I can slouch in my
chair, latte in one hand and mouse in the other.
---
Also gone, and good riddance: The trip to the photo lab, making sure
whether the solder side was right-reading or not, making sure the whole
damn thing didn't get printed upside-down, emulsion side down or up,
pinholes in the negative that had to be opaqued before the positive
filmwork could be made, Aarghhh...

Now it's Gerbers emailed out and PCB's back in a few days. Heaven!

Yeah. I had to drive down to Mountain View to Lorry Ray Photography,
the only people I could trust to shoot everything right. Then I had to
call to see when it would be done, and drive down again to pick up the
film. And we were always losing film. Their camera was basicly two
rooms with a lens mounted in the wall between them... they could shoot
1:1 D-size art, accurate to a couple of mils. Out of business now,
along with those bastards at Bishop Graphics.

John

 

[John Larkin]

On Wed, 02 Jul 2003 23:28:25 GMT, Spehro Pefhany <speff@interlog.com>
wrote:

On Wed, 02 Jul 2003 16:13:46 -0700, the renowned John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

Yeah. I had to drive down to Mountain View to Lorry Ray Photography,
the only people I could trust to shoot everything right. Then I had to
call to see when it would be done, and drive down again to pick up the
film. And we were always losing film. Their camera was basicly two
rooms with a lens mounted in the wall between them... they could shoot
1:1 D-size art, accurate to a couple of mils. Out of business now,
along with those bastards at Bishop Graphics.

The red and blue tape was even less fun than the black crepy stuff. We
usually sent the whole artwork out to the PCB manufacturer and let
them worry about the photography. I don't recall an original ever
getting lost.

It was pretty fast for low density single-sided boards, especially if
the donuts were on 0.1" grid (which most of them were in those days).
Unless you ran out of the 0.060" tape or the 0.030" tape, or the 0.14"
donuts..

Best regards,
Spehro Pefhany

Nobody I knew liked the color stuff. We did 4 pieces of pin-aligned
clear mylar: padmaster, top traces, bottom traces, and silkscreen;
occasionally we did a 4-layer, with the plane art cut out of rubylith.
Lorry Ray would sandwich layers to shoot the film, and would do tricky
stuff to make ground planes and solder masks from the padmaster art...
they could expand, contract, and, or, all sorts of stuff
photographically.

We'd make assembly and fab drawings by exposing the mylars directly
onto sepia paper. By playing with layer exposure times, you could make
cool faded-layer composites, even burn the title blocks in while you
were at it.

John

 

[Charles Jean]

I jumped into this thread a little late maybe. My computer's PS
decided to die after 5 years and have been OOS for about a week now.
If I'm correct, the OP had something to do with "no right angles on PC
trace-why?" I worked in the semiconductor industry 1966-1969 on jFETs
and in diffusion and microphotography(mask-making). We were at the
point of consisitently producing 2-5 micron lines on silicon in
production quanitites(I won't reveal the yields to this day-very
low!). But enough for a good profit. Our artwork was Ruby-Lith from
Kodak, I think. Mylar coated with a ruby-colored film. Manually design
the device topography on graph paper at 500:1 enlargement, overlay it
with Ruby-Lith, use an Exacto knife to score the Ruby-Lith, remove the
ruby film with a pair of tweezers, then do a 10:1 reduction photograph
of the master with a process camera onto a Kodak hi resolution glass
plate film. Then put the glass plate reduction into a machine that
would do a final 50:1 reduction repeatedly on another high resolution
plate. We were producing discrete components, but knew the writing on
the wall was "integrated circuits" and the holy grail would be one
micron geometries, or less. I remember reading a Kodak publication
that indicated when line geometries approached the wavelength of light
being used for fabrication, special precautions had to be taken to
compensate for diffraction of light during the photolithography
process. This included corner effects, called
"vignetting"(sp?)-rounding of corners due to optical effects, such as
diffraction. There were even suggested modifications that could be
made to the original artwork so that the end photomask wound up
*being* a right angle. It occurred to me that maybe some of this
thinking may have spilled over into the PCB end of things as their
requirements for dimensional tolerances became more stringent.
Anyway, none of the above had anything to do with electrical "crowding
at the corners"(not saying they didn't exist), just optical problems
at small dimensions. As a point of reference, the best resolution lens
we could get at the time was a Nikon(650 lines/mm).


On Wed, 02 Jul 2003 17:38:43 -0700, John Larkin
<jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

On Wed, 02 Jul 2003 23:28:25 GMT, Spehro Pefhany <speff@interlog.com
wrote:

On Wed, 02 Jul 2003 16:13:46 -0700, the renowned John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

Yeah. I had to drive down to Mountain View to Lorry Ray Photography,
the only people I could trust to shoot everything right. Then I had to
call to see when it would be done, and drive down again to pick up the
film. And we were always losing film. Their camera was basicly two
rooms with a lens mounted in the wall between them... they could shoot
1:1 D-size art, accurate to a couple of mils. Out of business now,
along with those bastards at Bishop Graphics.

The red and blue tape was even less fun than the black crepy stuff. We
usually sent the whole artwork out to the PCB manufacturer and let
them worry about the photography. I don't recall an original ever
getting lost.

It was pretty fast for low density single-sided boards, especially if
the donuts were on 0.1" grid (which most of them were in those days).
Unless you ran out of the 0.060" tape or the 0.030" tape, or the 0.14"
donuts..

Best regards,
Spehro Pefhany

Nobody I knew liked the color stuff. We did 4 pieces of pin-aligned
clear mylar: padmaster, top traces, bottom traces, and silkscreen;
occasionally we did a 4-layer, with the plane art cut out of rubylith.
Lorry Ray would sandwich layers to shoot the film, and would do tricky
stuff to make ground planes and solder masks from the padmaster art...
they could expand, contract, and, or, all sorts of stuff
photographically.

We'd make assembly and fab drawings by exposing the mylars directly
onto sepia paper. By playing with layer exposure times, you could make
cool faded-layer composites, even burn the title blocks in while you
were at it.

John

Yeah! By Cracky! We programmed the IBM 650 in machine
language by the seat of our pants! When we ran out of
1's we used l's, and when we ran out of 0's we used O's.
YEEE-HAAA!

 

[Fast Eddy]

I was told it was because the electronicals would fly off the edge of the
track
due to the speed they are travelling.

Rather like a car on a racetrack going really fast and coming to a corner
and sliding off.


You may have to clean out the box that the circuit is in because of the mess
it will make.

PS you will need a good eye cos you can't see them too well, but they are
there somewhere.


Edward B Tweedel
Oxford
UK

 

[John Larkin]

On Tue, 15 Jul 2003 01:57:34 GMT, Chuck Simmons
<chrlsim@earthlink.net> wrote:

Fast Eddy wrote:

I was told it was because the electronicals would fly off the edge of the
track
due to the speed they are travelling.

Rather like a car on a racetrack going really fast and coming to a corner
and sliding off.

You may have to clean out the box that the circuit is in because of the mess
it will make.

PS you will need a good eye cos you can't see them too well, but they are
there somewhere.

Edward B Tweedel
Oxford
UK

Are you reading Divinity? Tweedel DD has a nice ring to it.

That was Dum.

John

 

[Pat Quinn]

"BM" <brandon(underscore)melland@hotmail.com> wrote in message news:<1L0La.1667$7e.1222@nwrddc04.gnilink.net>...

I was told the other day that there are no right angle traces on PCBs (the
traces go to something like 45 degrees between perpendicular traces) because
of something to do with something or other. Could something please explain
this or point me to some resources so I can book up.

Thanks

-BM

Here are my 2 cents:

1) across diagonals, you can pack traces closer
2) current density in the corner is fairly low, thus it is only
semi-functional metal
3) breakdown voltage will be lower off of sharp edges
4) a square corner will lower the impedance of a controlled-impedance
line at the corner and may lower signal integrity

-pq
Portland, Oregon

 

[Harry Conover]

"BM" <brandon(underscore)melland@hotmail.com> wrote in message news:<1L0La.1667$7e.1222@nwrddc04.gnilink.net>...

I was told the other day that there are no right angle traces on PCBs (the
traces go to something like 45 degrees between perpendicular traces) because
of something to do with something or other. Could something please explain
this or point me to some resources so I can book up.

Thanks

-BM

It may very well have to do with the reason that fillets are used
whenever connecting to pads.

When I was first learning PC board layout 30 years ago, I was taught
that this reduces the problem of solder bridges when wave soldering.
This made sense to me, and so I still always use fillets when
connecting to pads.

I suspect that this is the same reason that right angle turn on PCB
laysouts should be avoided, in that they attract the formation of a
solder bridge that could very well short to other nearby conductors.

Harry C.

 

[Eric Immel]

Fast Eddy wrote:

I was told it was because the electronicals would fly off the edge of the
track
due to the speed they are travelling.

Rather like a car on a racetrack going really fast and coming to a corner
and sliding off.


You may have to clean out the box that the circuit is in because of the mess
it will make.

PS you will need a good eye cos you can't see them too well, but they are
there somewhere.


Edward B Tweedel
Oxford
UK

Don'cha hate it when electrons spill everywere?

I seem to recall, through a FeCl3 haze, something about acute angles
causing undercuts in the etching process.

EI

 

[ED]

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:WvydnRtprsl6TYrQnZ2dnUVZ_rOdnZ2d@supernews.com...

Chuck Simmons wrote:
BM wrote:

I was told the other day that there are no right angle traces on PCBs
(the
traces go to something like 45 degrees between perpendicular traces)
because
of something to do with something or other. Could something please
explain
this or point me to some resources so I can book up.

There used to be a significant undercutting issue in right angle bends.
This could be reduced by mettal filling unused areas or by avoiding
right angle bends or both. In modern board processing, I rarely see
undercutting anywhere. BTW, the same difficulty exists in some IC
processes and metal fill is used to reduce the problem.

Chuck

http://www.montrosecompliance.com/Technical_papers/corners-Japan.pdf

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=801409