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Electrically-Conductive Tapes application advice?

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Electrically-Conductive Tapes application advice? | 26 July, 2009

Hi everyone,

I need to connect a cylindrical disc device (piezo ceramic sensor) to the PCB trace without using high temp solder. I plan to use "3M™ XYZ-Axis Electrically Conductive Adhesive Transfer Tape 9719" to connect the device to the PCB trace to replace the need for soldering but i am not sure if this method works? Or is sticking a copper strip over it works better (see picture)?

I have read in this forum about the use of aluminum tapes to secure thermocouples but i am not sure if it can be used to replace soldering.

The sensor will be hit by an ejector pin and will produce a voltage difference between the top and bottom surface of the sensor which i need to measure. I was thinking that when the ejector pin hits the tape/copper strip, it will close the loop and i can measure the voltage readings? The reason i cant use high temp solder is because the ejector pin will hit the solder bead thus damaging the connection to the sensor. Using solders will also cause protrusions which i need to keep to less than 1mm. I have attached pictures of my application. Hope it helps!

I am sure some of you can give some good advice.:) This is my first time doing a PCB. Thanks in advance though.

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Electrically-Conductive Tapes application advice? | 28 July, 2009

It's possible that there is limited application of "3M™ XYZ-Axis Electrically Conductive Adhesive Transfer Tape 9719" similar to your intended use. What do 3M™ application types say?

Certainly high temperature soldering would make a mess of a piezoceramic sensor. So, why aren't you using a low temperature solder?

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Electrically-Conductive Tapes application advice? | 28 July, 2009

Thanks Davef!

3M's product description of "3M™ XYZ-Axis Electrically Conductive Adhesive Transfer Tape 9719 is suitable for attaching low surface energy (LSE) EMI shields to electronic and electrical devices where high temperature (up to 400C) is required.". However, it's type is also used for "For connection/bonding/grounding flex circuits, printed circuits boards, EMI/RFI shields & gaskets". So, i was wondering if it could be used to provide electrical connection to the device.

The main reason i wrote high temp soldering is because my operating temperature is about 200 degrees C in the molding machine 24/7. I would not want the solder to melt. I am not familiar with the types of solder,any advice?

So, if using copper strips method is easier, how can i control the solder protrusion height to less than 1mm? Can hand soldering achieve that? How about using a high temp adhesive tape to tape it down instead? But this way, it is not easy to mass manufacture and only suitable for prototypes right? ....Any advice anyone? I am more concerned about how to connect the sensor to the PCB tracks.....

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Electrically-Conductive Tapes application advice? | 31 July, 2009

If the sensor can survive the 200C in the molding machine, then could it not survive Pb-free soldering? Maybe not convection reflow, but it should be able to survive vapor-phase reflow. I would control solder height by controlling the amount of paste applied (stencil thickness).

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Electrically-Conductive Tapes application advice? | 1 August, 2009

Thanks on the advice isd.jwendell! Yes, the piezo ceramic has a Curie Temp of about 800C, so its safe operating temp should be around 300-400C. How about if my PCB is a prototype, would it be more economical to use hand soldering or just manually applying solder paste around the copper strip and heat it up with solder iron? I guess for my design (see picture at first post), mass manufacture will be a problem right? If anyone has a better idea, feel free to share!! :)

Anyway, if i were to use a high temp adhesive tape to tape down the copper strip instead of soldering it with solder paste, is there any problems in the long run if the PCB is sandwiched tightly between Teflon insulator plates?

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Electrically-Conductive Tapes application advice? | 1 August, 2009

Unfortunately, I don't see any image. If your part will survive 300C then even convection reflow should work. The use of paste and reflow ovens are for when you move to production quantities. It sounds like you could hand solder your prototypes (proof-of-concept) with wire-core solder, but you will lose the repeatability that (should) come with production techniques. When hand soldering your prototypes, remember that the type and quantity of flux is very important. Not all flux are created equal.

The problem that I see with using tape to fasten parts is that it is a manual operation. This may increase cost when moving to full-scale production. Manual operations can also suffer from repeatability problems, ie. one person does it right and one person does it wrong. The use of tape (manual operation) and quality control can be addressed in the production cycle though, so it is still a viable alternative. What is the cost of the 3M conductive tape?

I am glad to see that you are considering manufacturing issues now, instead of later. It will make the jump to manufacturing much easier.

Can you repost the image?


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Electrically-Conductive Tapes application advice? | 1 August, 2009

Here's the link to the image. It seems the forum's image feature is down?

X-section view..

Copper Strip with Adhesive Tape idea...

Conductive Tape idea...

The 3M tapes are not expensive. Well, looking at my current design of the x-section, it seems mass production will be a problem since one side of the copper strip has to be soldered/taped on before the sensor can be inserted. Most probably, the PCB will be low volume(<100) so it should be ok to do manual on all boards.

It's just that i had to keep the solder protrusion/electrical connection as low profile as possible(<1mm high). I will try controlling the stencil thickness you mentioned. And also the adhesive tape method which is easier to apply as well as better control on protrusion height. Do you think so?

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Electrically-Conductive Tapes application advice? | 2 August, 2009

Now that I've seen the pics...

Soldering could work just fine. If you are going for large production then you could get copper discs cut and mounted in tape carrier ($$). This would make it very easy for automated equipment to assemble. Mounting a disc to both sides will require passing the PCB through the whole process twice. Once for one disc, the second time for the sensor and final disc.

My main concern would be the PCB thickness tolerances. If you use the solder process then the sensor cannot exceed the PCB thickness, or the discs would not solder properly. How much will the sensor expand (vs PCB expansion) at soldering temperatures? Will the sensor need to be soldered to the discs?

Because of the potential problems when soldering, and the quantities mentioned, I think that the 3M adhesive is the best choice. You can also get the tape precut to the exact shape you desire ($$), if required.


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Electrically-Conductive Tapes application advice? | 2 August, 2009

Wow! Thanks Jim!.

When the ejector pin hits the piezo ceramic sensor, the sensor will produce a voltage difference between the top and bottom surface(that's why i need to connect the tracks on both sides) which i will measure. The sensor does not need a power source, all it needs is a dynamic force/impact to create the voltage difference.

So, the copper disk should not need to be soldered (havent tested yet) to the sensors since during the ejection process, the ejector pin will be in contact with the sensor(and with the copper disk) for a few seconds. I will try the 3M tape with copper disk method and report back on the results when i have it.

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