Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

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Screen printing glue for wave soldering SMT components.


Screen printing glue for wave soldering SMT components. | 26 May, 2000

We have no experience in printing glue only in dispencing for short runs. We are finding that our gluing volumes are going up and want to look at screen printing as an option. We are placing 0805 and 1206 chips, melfs, sots and ics. What are the advantages and pit falls? what sort of stencil (type and thickness) do we use? do we use the same patterns as for dispensing? what are the glues like to clean off stencils? etc etc etc. Can any advise.

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Re: Screen printing glue for wave soldering SMT components. | 26 May, 2000

For the past year now we have been printing adhesive with no real problems. Our printing ranges from 0603's to SOIC using a variation of aperture sizes and metal thickness foils. The crucial parameters are :

aperture sizes : These obviously depend on the component to be glued, pad spacing is crucial as to big of an aperture will contaminate the solder pads, will give a greater stand-off and cosmetically look wrong, and to small of an aperture will give you problems with poor release from your stencil leading to insufficient's and missing components.A general guide line would be ; 12-16 thou diameter for 0402 16-20 " " " 0603 20-24 " " " 0805 40-47 " " " 1206 40-43 " " " mini melfs 40 " " " sot 23 Like I said the above mentioned is only a guideline. One advantage of printing adhesive is that all screen apertures can be manufactured in all shapes and sizes. The way forward would be to develop a test screen with a range of aperture shapes and sizes and see what best suits your process not forgetting the stress and flex test.

Glue selection : Again important,whatever you select ensure it has good green strength. Many glue manufacturers out there will try to sell you a glue which will be suitable for dispensing as well as printing, dont fall for this sales pitch and ask for one which is specifically designed for printing.

Print parameters : Critical. Make sure your under screen cleaner is switched off. Your speed, print gap and separation speed will govern your glue volume and whether you have peaks on your dots. Different print cycles can also be used.

Profile : Make sure your product sees 150 deg between 60 -90 secs.

I hope the above will set you on your way. Trust me this is not rocket science, If you can print solder paste then YOU can print adhesive. Please do not hesitate to contact me via email if you nedd further help or assistance.

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Re: Screen printing glue for wave soldering SMT components. | 29 May, 2000

Hi Buddy, We've tried shifting to this process before and from our point of view here are some of the advantage and disadvantages that we discovered.

Advantage 1) Cheap Equipment cost as you just need to use your Solder Paste Printer rather than buy a dispensing equipment. 2)Process speed is too fast !!!

Disadvantages 1) Cleaning Stencil. It is difficult to clean or remove the adhesive from the stencil compare to solder paste since it is not made up of balls. You can use smart sonic though. Inquire from them on their Model 2000 Stencil Cleaner. 2. Material waste. The materials or adhesives left on the stencil is considered a waste since you cannot keep it for the next day operation unless you are running continues operations 7 days a week, 24 hrs. a day. 3. The stencil thickness determines the deposition volumes and is fixed and can't be altered. This limits the range of components standoffs like SOIC's unless your bottomside components are only chips. We did not continue investigating this as most of our products have SOIC's on the bottomside. 4. Aperture dimensions and shape. The smaller the aperture the greater the difficulty in release and the more prone to clogging your stencil will be during the process. 5. Line balancing. If you have a tact time of 3 mins. on your 1st chipshooter and 10 secs. for the printing of adhesive, just imagine the bottle neck that you would have. 6. Environmental concerns and Exposure of glue. This is a topic that you need to discuss with your adhesive supplier.

Hope the above info's will help you !


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