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Simeple ACF TAB/COF bonding pressure?

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    Simeple ACF TAB/COF bonding pressure?

    I have came up with a design in my head for a lever action hot bar press. You can buy a lever style press and modify it slightly to easily achieve a lot of downwards force. You can use a scale to calibrate what lb force any certain position of the lever.

    But what I am trying to figure out is this - the ACF that I am debating buying is rated for 2 Mpa at ~200C for 20 secs. When converting Mpa to PSI I get around 290-300 PSI.

    The head of the machine, the hot bar, will have a much smaller area than square inches. So my question is if you have a hot bar head that has an area of 3-4mm x 45mm, then how much force is actually needed? Wouldn't it be much less than 290 psi or 2 MPa?

    The reason I ask is because 300 pounds of downwards force seems like it would be WAY to much pressure to exert on a pcb or an LCD. I would think that 40-50 actual pounds pressing down over such a small area would be more than plenty but I am not good at math when it comes to converting pressure over an area. It just seems that 290 lbs of force is WAY to much.

    I have the plan for this hot bar manual press figured up in my head and can easily source a T tip soldering iron and magnifying glass to align and set the COF back in place, but I just am not sure if it actually takes THAT much pressure. 2 MPa spread over an area of 3mm x 45 mm, would that really require 290 lbs of force? That would be like 1 and a half people standing on that small of an area.

    Any help would be appreciated and thanks

    EDIT: hopefully I put this in the right section. Should I put it over in the TV trouble shooting area? I figured this was a "general electronics technical discussion" but I am not sure. I just want as many people as possible to see it in hopes I get some insight.
    Last edited by james28909; 08-21-2020, 07:13 AM.

    #2
    Re: Simeple ACF TAB/COF bonding pressure?

    This is the instruction manual for a tab COF bonding machine. It details the process of applying the double sided tape.
    https://www.slideshare.net/deoarshi/...ne-user-manual
    Machines have definitely come down in price, they were much pricier a few years ago.
    https://www.alibaba.com/showroom/tab...g-machine.html

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      #3
      Re: Simeple ACF TAB/COF bonding pressure?

      I was able to source a lever press from my uncle who worked on jewelry. There is plenty of room to for it to reach the PCB and if needed the LCD too. It has a heavy duty steel construction and has a single rod that presses down.

      I think I can buy a smaller heat plate. Then weld me a plate on the bottom of the rod. I will polish the bottom of the plate so it is perfectly smooth and flat as possible then mount the heat plate on the plate I welded on the bottom of the rod.

      What I'm trying to figure out is how to cool it rapidly though. I'm thinking of using some kind of water cooling and drilling some holes and somehow attach some water pipes to the heading block so I can cool it off quickly. Another thing I thought about is compressed air in a can lol. Any thoughts on this?

      I can use one of these t tip soldering iron to pre bond the act and get everything aligned with a magnifying glass. Then put it in the press and have it at operating temp. The heat plate will be on a variable output power supply so I can control the temp. I have a multimeter that has a thermocouple on it that is pretty accurate. I have an infrared thermometer that I can calibrate with and get it real close to the right temp.

      Then all I need to do is get me a weight scale and press and mark the position of the lever when the right weight is applied.

      One other thing is what to use to protect the cof from the heat temps. I guess I will do some more research but I have this bad as TV and all I need to do is reattach one cof that accidentally got half way pulled off :l

      I'm trying to make something that will be very cost effective and something that could actually work. Anyone have any thoughts on this? Any ideas would be welcomed
      Last edited by james28909; 08-22-2020, 10:37 PM.

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        #4
        Re: Simeple ACF TAB/COF bonding pressure?

        Well I have figured everything out except for how much actual pressure to apply.

        I have gotten me a lever style press from my uncle, borrowed my dads wire welder.

        Make a block that has a head that comes down to a small area (2-3mm x 45-50mm) and make sure the bottom is as flat as possible. I will drill a hole through the width of the head and then tap some threads on each side to connect some tubing for CO2 for cooling quickly. Then attach my thermocouple and the heatplate to it.

        Attaching the head is going to take a few though because it has to come down flat, so I will have to attach the head in a way that will allow me to adjust the pitch of the head.

        The idea is to prebond the COF to the pcd with a T tip solder bar with teflon tip and use a usb microscope (something like this - https://www.ebay.com/itm/AmScope-10X...YAAOSwRg9eLzSq) that will allow me to align everything perfectly. Then once everything is good, turn on the heat plate and wait for it to get to ~210c, put a protective film in between the COF and heat head, and then drop it down and press and hold an unknown amount of pressure (if anyone knows how much then please share) for around 15-20 secs or whatever the acf calls for. Then turn off the heat head and open the valve for the co2 to flow through the head which would cool it quickly.

        Seems redneck as hell but I have a good image in my head what to do. The only thing I have to figure out now is how much pressure in lbs force (not mpa) because 290 lbs spread across an area 3mmx40-50mm seems extreme.

        Or how would I even convert 290 psi to an area of about 3mm x 45mm? How could I find that out? If I knew this I would be set and could order the ACF

        once I build it I will post pictures. I do need to figure out how to press with precision, maybe have some weight on a rope and tie it around the handle while its bonding LOL.
        Last edited by james28909; 08-30-2020, 12:46 AM.

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          #5
          Re: Simeple ACF TAB/COF bonding pressure?

          Sorry for spamming my own thread here but I went over to reddir r/askmath and they did the math and figured up that 2 Mpa spread over an area of 2mm x 45 mm is about 40.5 lbs of force.

          Ill paste the math here so anyone else can find it easy.

          So first we need to know the formula for pressure:

          Pressure = Force/area

          Then we need to convert the units so we can do the calculations:

          2MPa = 2,000,000 Pa = 2,000,000 N/m

          2mm = 0.002m 45mm = 0.045m

          Then work out the area in m2

          0.045*0.002 = 0.00009m2

          Then we can work out the Force:

          Force = Pressure*area = 2,000,000*0.00009 = 180N ≈ 40.5 lbs of force.
          and

          2 MPa = 2 N/mm2

          A = 2*45 mm2 = 90 mm2

          F = 2 N/mm2 * 90 mm2 = 180 N

          180 N = 40.5 lb
          so looks like it is not that much pressure at all and I will be able to easily manage this with my modified lever style hot bar press.

          Still not sure if I want to make my own head or order a thermode and thermocouple and some heating element that will heat quickly within 3-5 secs.

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