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Adhesive printing



Adhesive printing | 28 January, 2002

Looking for feedback from anyone with experience with adhesive screen printing. Currently we are dispesnsing with Unversal's GDM, but are looking into the process of printing the adhesive. Just wanting good and back feedback from this process.

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Adhesive printing | 28 January, 2002

Printing with adhesives is no big deal so don't let the sales types try to mystify the process and convince you that they have the only stencils/adhesives/knowledge that can possibly get you through this "trying time" - at a price. Start with 0.010" thick stencil ( stainless or brass is fine ) with a print gap of 0.005" plus,- you'll have to find what's best for you. I set the squeegee blades to board height plus stencil thickness so that the stencil rolls off the pcb as the squeegee travels. I don't use any delay times or slower speeds for stencil release - but again youll have to find what suits you. Adhesive behaves in a different manner to solder paste, so your dot height is dependant on your aperture size - not the stencil thickness. The glue "pulls" away with the stencil release to achieve this. Try these sizes to start with, 0402 = 0.015", 0603 = 0.020", 0805 = 0.025",1206 = 0.030", SOP = 0.040" That should get you going. Make up your library in the cad package with these dots built ito your component in a layer that nobody uses, replace the original components with your library components - do this one by one to begin with to make sure there are no uglies ( offsets/rotations etc. )in there!. Send your gerber file for the "dot" layer to your stencil people and that's it. Any decent PC printer will allow you to do an accurate print on transparency film at 1:1 so you can check you file against the pcb before you send it off. Line up by doing a mylar print and you're away! Easy. You could ( should ) make up a test stencil with different sizes and spacing etc to see what is going to work best for you. I use Amicon D125F adhesive. Check the archives as there should be plenty in there. I hope your not glueing for double-sided reflow. Let's know how you do.

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Adhesive printing | 31 January, 2002

What tempurature is used to cure the glue and for how long?

What happens if a component that has been glued and soldered needs to be removed?


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Adhesive printing | 31 January, 2002

The whole process counldn't be easier. The sales reps' try to turn the whole thing into some crazy black art-its not.

The stencil supplier will have their own standard 'glue dot' configurations, and 9 times out of 10 these are more than adequate. As you purchase more stencils and gain expierence with the process you will start and build up your own unique 'glue' configurations. i.e. Melfs - instead of two dots, use a slot. The component therefore has more contact with the adhesive and stops them from rolling.

To remove the components - suck the solder as normal, and remove the component with a pliers etc. The glue can then be removed by heating it up with a hot-air gun and simply 'flick' it off.

The oven profile is also very simple. Depending on the type of adhesive you select, the manufacturer will provide a 'Technical Data Sheet' stating the storage parameters, the working environment and the oven profile.

Do what it says on the packet, and you can't go wrong.

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Adhesive printing | 1 February, 2002

Whoa! I beg to differ my friend.

The cure profile is VERY critical in Adhesive curing, especially if your are screen printing. When you screen print adhesive you are leaving it exposed to the atmosphere for a period of time. SMT adhesive by nature is VERY prone to moisture absorption. So unless you have humidity control in your facility, I would warn you to take caution. The rate of rise on your profile should never exceed 2 deg. C rate of rise a second. If there is moisture present in the adhesive and you exceed this rate of rise porosity will occur inside the cured dot. That opens you up for many different types of failures, and guess what, you will never visually see any any problem because the dot is under the part. I would highly reccomend that you talk to your adhesive supplier about these issues.

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