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Conductive adhesives

 

Has anyone tried using conductive adhesives to repair connections such as IC package pins to a circuit board? I have two broken pins( #11 and #12) at the PROM IC on the DR7 circuit board. I believe I can solder them back with new leads from the circuit board with much ?care and a low power soldering iron, ?but I was thinking this might be a good application for?conductive adhesives, but I don't have any experience with them. If I befoul the PROM IC I don't know where I'd find another one.

Side comment--Don't now how those pins got broken, looks like mechanical issue, not corrosion. I haven't moved the rig in several years, I only opened up to clean the board connections as I was experiencing the common problem (as I understand it) of runaway frequency. In my case the frequency would run away 80 and 20 meters bands, and then it started run up to 99.xxx mHz on all bands and bounce around there.

Thanks for any insight you can give.
--
Ken KA4MIE
 

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Most conductive adhesives you hear about are actually insulating adhesive vehicles loaded up with acicular pieces of metal, generally magnetic, so they can be preferentially oriented in one direction. This leaves a matrix that is a good conductor in the direction in which the metal particles are oriented and a good insulator perpendicular to the metal particles. This structure can Abe slit into a sticky film that conducts in the up/down plane (Z axis) and insulating in the XY plane, the plane of the film. This can be applied directly across rows of contacts and then be mated with similar contacts on the other part to be bonded. This connects every pair of contacts without interfering with one another. This is the method by which most ribbon connectors are attached to PC boards these days.

There are conductive paints as well. These are generally epoxy resins loaded up with metal, usually Silver, to the point at which the desired conductivity of the final cured film is quite high. Very carefully applied, this can be used to paint new traces onto a PC board. However, you need to use the paint to make the entire trace and contacts at both ends because you cannot solder to the finished material.

There once was an adhesive product known as “Circuitrace”, which consisted of metallic tape, in narrow strips, with a conductive PSA (pressure sensitive adhesive) on one side. This could be used to lay down new traces and I believe it could take carefully applied solder.

Gary

W0DVN

On Jan 18, 2023, at 1:02 PM, kmg53 via groups.io <kmg53@...> wrote:

Has anyone tried using conductive adhesives to repair connections such as IC package pins to a circuit board? I have two broken pins( #11 and #12) at the PROM IC on the DR7 circuit board. I believe I can solder them back with new leads from the circuit board with much ?care and a low power soldering iron, ?but I was thinking this might be a good application for?conductive adhesives, but I don't have any experience with them. If I befoul the PROM IC I don't know where I'd find another one.

Side comment--Don't now how those pins got broken, looks like mechanical issue, not corrosion. I haven't moved the rig in several years, I only opened up to clean the board connections as I was experiencing the common problem (as I understand it) of runaway frequency. In my case the frequency would run away 80 and 20 meters bands, and then it started run up to 99.xxx mHz on all bands and bounce around there.

Thanks for any insight you can give.
--
Ken KA4MIE

 

To answer the question of why the "prom" has some of the legs broken off. That is how you enter the band you want. It is a diode matrix and there is a chart to tell you which pin set you need. You can make a replacement with a chip socket and diodes if chip is Unobtainium. The chip internal diagram is on the internet, to refer to when setting up a replacement.
Good luck, Nick......wb7pek
 

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Pretty simple “PROM” technology. I remember it well. Empty headers were commonly available and diode were cheap (Still are) and, at the time, most hams still knew how to use a soldering iron…

Gary

W0DVN

On Jan 19, 2023, at 5:59 PM, Nick Pair via groups.io <daweezil2003@...> wrote:

To answer the question of why the "prom" has some of the legs broken off. That is how you enter the band you want. It is a diode matrix and there is a chart to tell you which pin set you need. You can make a replacement with a chip socket and diodes if chip is Unobtainium. The chip internal diagram is on the internet, to refer to when setting up a replacement.
Good luck, Nick......wb7pek
 

Guys, the OP specifically referred to the PROM on the DR7. You are thinking of the diode arrays on the AUX-7.

73

-Jim
NU0C

On Thu, 19 Jan 2023 18:05:47 -0600
"Gary Follett" <xntrick1948@...> wrote:

Pretty simple “PROM” technology. I remember it well. Empty headers were commonly available and diode were cheap (Still are) and, at the time, most hams still knew how to use a soldering iron…

Gary

W0DVN

On Jan 19, 2023, at 5:59 PM, Nick Pair via groups.io <daweezil2003@...> wrote:

To answer the question of why the "prom" has some of the legs broken off. That is how you enter the band you want. It is a diode matrix and there is a chart to tell you which pin set you need. You can make a replacement with a chip socket and diodes if chip is Unobtainium. The chip internal diagram is on the internet, to refer to when setting up a replacement.
Good luck, Nick......wb7pek
 

I have some experience using silver loaded epoxy.? The epoxy is a slurry containing tiny silver plated nickel spheres.? It works, we used it in production back when I worked for a microwave component company.? I recall that it was costly and had a short shelf life.
 

I used??in a project a year or two ago to bond wires to magnets so I could pass electricity through them. The epoxy worked fine, though there are some comments about it being a nasty chemical that you'll want to be careful with.

Supposedly heat damages the magnets, which is why I chose to epoxy rather than solder.

Solder would be my first choice.

Scott
 

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No “supposedly” about it. If you heat a magnet above its Curie temperature, it will no longer be a magnet.

Gary

W0DVN

On Jan 21, 2023, at 6:12 PM, Scott Baker <smbaker@...> wrote:

I used??in a project a year or two ago to bond wires to magnets so I could pass electricity through them. The epoxy worked fine, though there are some comments about it being a nasty chemical that you'll want to be careful with.

Supposedly heat damages the magnets, which is why I chose to epoxy rather than solder.

Solder would be my first choice.

Scott

 

(Belated) Thanks, Nick. I have time again to work on it. I also have the TR-7 service manual which explains what the chip is doing, but I was unclear about why the two legs were broken. I'll be looking up that chip diagram to see how it does what it does.
--
Ken KA4MIE
 

Another belated thanks to all others who replied.?
--
Ken KA4MIE
 

What the PROM does is it "monitors" the N-Code fed to the Translator board from the DR7 for two purposes. The first is to disable the action of the Up or Down button when your reach the edge of a band switch segment. This keeps you within the limits of the high pass and low pass filter sections of the band switch. The second is to keep your from transmitting outside of a ham band. It is pretty clever really. The address lines of the PROM follow the N-Code and the contents of the PROM memory at any given address will either enable or disable the buttons as needed and also operate Q9001 to inhibit transmit in 500 KHz segments that do not contain a ham band.

The radio will work perfectly well with the PROM removed entirely but you would need to be mindful of the filter edges. Worst case, you could smoke a low pass section by transmitting above it's cutoff frequency or transmit unwanted harmonics.

A known failure mode of these PROMS is one of the address lines going shorted which disrupts the N-Codes. This may be from careless handling causing ESD damage as the PROM inputs are tied directly to the male Molex pins on the bottom of the board.

PROMs are available if you need one.

73

-Jim
NU0C

On Fri, 24 Mar 2023 15:11:39 -0700
"kmg53 via groups.io" <kmg53@...> wrote:

(Belated) Thanks, Nick. I have time again to work on it. I also have the TR-7 service manual which explains what the chip is doing, but I was unclear about why the two legs were broken. I'll be looking up that chip diagram to see how it does what it does.
--
Ken KA4MIE

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