PCBs are Fundamental

Thread Starter

Yaakov

Joined Jan 27, 2019
3,464
The PCBs of today are essentially the same as the ones today. A sandwich of copper and some sort of insulating material. Sure we have better materials and techniques but it seems that PCBs are something like resistors, capacitors, and the like—they are just something we use to build practical devices because they are needed.

There's been some discussion about "how it used to be done". When I ran across this, three things struck me:

1. It seemed very old.
2. It is from 1969 which is in my lifetime and so it seems like it couldn't be as old as it is.
3. The revolutionary changes in tools and techniques for PCBs happened very fast.

Yes, I was a kid at the time, but it really doesn't see like it could be 50 years ago. In any case, if you want to see how it used to be done, here's Tektronix and how they did it. And they were definitely among the very best. Just a little CNC but a lot of half sleeve shirts and pencils.

 

AlbertHall

Joined Jun 4, 2014
11,498
I made some PCBs with etch resist tape and dot. Of course you only get one go at that. If you need another one then you must start from scratch.
 

Thread Starter

Yaakov

Joined Jan 27, 2019
3,464
I made some PCBs with etch resist tape and dot. Of course you only get one go at that. If you need another one then you must start from scratch.
Oh boy, I remember tape and resist pens very well. I have to admit my PCBs were not exactly works of art.
 

nsaspook

Joined Aug 27, 2009
8,652
Companies like IBM had very advanced PCB board technology in the 60's/70's. The main limitation of what was available commercially was cost as usually only governments could justify or have the need for that level of circuit complexity back them .The Saturn V rocket computer systems is an example.


http://www.righto.com/2020/04/a-circuit-board-from-saturn-v-rocket.html
Each page could hold two circuit boards, one on the front and one on the back. The printed circuit board has 12 layers, which is a remarkably high number for the 1960s. (Even in the 1970s, commercial PCBs typically had just two layers.) The page has a 98-pin connector, with 49 connections to each PCB. The two boards were connected by 30 "thru pins" at the top of the board. The top of each board also has 18 test connections; these allowed signals to be probed while the boards were installed. (IBM reused this page construction in its System/4 Pi aerospace computers.15)

The board I examined had been forcibly separated from the other board in the page. The photo below shows the back of the board. The thru-pins are visible at the top; they would have been connected to the other board. At the bottom, the 49 connections from the connector to the missing board are visible. Some of the board's insulation has been removed, showing the 12 vias at each ULD module position. These provide a connection from a chip pin to any of the 12 layers of the circuit board.
https://books.google.com/books?id=4SUDAAAAMBAJ&pg=PA94&lpg=PA94#v=onepage&q&f=false
Dr. Wernher von Braun



Some of the earliest circuit boards I worked on were hybrid tube/transistor boards from early digital cryptographic equipment designed and built in the 50's.
kwr37_vv_card.jpg
 
Last edited:

nsaspook

Joined Aug 27, 2009
8,652
That's fascinating. I've never seen anything built that way.
NSA built those devices. It was amazing technology for the period. The inner workings of these old digital devices unfortunately are still classified so we can't go there.

The devices were still online and operational until the Walker spy ring completely compromised the series.
http://www.jproc.ca/crypto/kwr37.html
On 28 May 1985, John Anthony Walker and his son, Michael Lance Walker were indicted by a Federal grand jury in Baltimore, Maryland on six counts of espionage. John A. Walker, a retired Navy warrant officer who had held a TOP SECRET crypto clearance, was charged with having sold classified material to Soviet agents for the past 18 years. During his military career, Walker made some investments in which he lost money. To make up for his losses, in late 1968 at the age of 30, Walker went to the Soviet Embassy in Washington, D.C., and offered his services for purposes of espionage. He compromised key cards used for enciphering messages and also provided information on the encryption devices themselves. At least a million classified messages of the military services and U.S. intelligence agencies were compromised by Walker. A Soviet defector said the KGB considered this the most important operation in its history. Michael L. Walker, a petty officer assigned to the USS Nimitz, was accused of providing classified Navy documents to his father for sale to the Soviets. Fifteen pounds of classified material were in his possession at the time of his arrest on the Nimitz. On 28 October 1987, both John and Michael Walker pleaded guilty to espionage under a plea agreement. On 6 November 1986, John Walker was sentenced to two life terms plus 10 years to be served concurrently. Michael was sentenced to 25 years. John Walker's arrest was the result of an FBI tip from his former wife.
 

GetDeviceInfo

Joined Jun 7, 2009
1,875
My earliest boards were Pico tapes and pads, contact printed onto MG photo resist treated boards. I still occasionally cut a board, but inkjet replaces the tapes and pads.
 

LesJones

Joined Jan 8, 2017
3,476
I remember making my first PCBs in the early 1960s when I was in my late teens. I had not seen copper laminate board for sale so I glued thin phosphor bronze sheet (Which my father got as offcuts from work.) to paxolin sheet with contact adhesive. I then painted the pattern using cellulose paint. I etched them using nitric acid. (I did not know about ferric chloride at the time.) I had to be quick soldering as the adhesive tended not to work well at soldering temperatures.

Les.
 

eetech00

Joined Jun 8, 2013
2,568
Back in early 70's, we used to use tape on mylar scaled up 4 times. Then "beep" the taped traces to ensure it matched the schematic. Crude but effective....;)
 

ElectricSpidey

Joined Dec 2, 2017
1,796
I owned and ran a small screen printing shop for 28 years, and many times considered using the resist method to make my boards instead of using proto boards...but the daunting task of drilling the holes always dissuaded me from even trying.

Do I regret never trying...yea maybe.
 

jgessling

Joined Jul 31, 2009
82
That video was quite interesting, especially to a software guy like me. I had actually never seen a wave soldering machine until about 1996. I was working at AMD in the department that managed the computers that ran the FAB. (Sunnyvale CA). We were turning out 486 chips like crazy and doing everything we could to make even more. The VMS (workstream) based terminals in the FAB were a constant problem because the techs kept fiddling with the settings as kind of a game to mess up the next shift. There was a local company that we went to visit that was trying to sell us compatible sealed units that the techs couldn’t mess with. That’s where I saw the wave soldering line on our visit over there. Didn’t work out. AMD had lots of problems after that but it was fun while lasted.
 
Top