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Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons

steveZ

#2839

Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 3 October, 2000

Had cheacked the archives but I didn't see much about their comparison:

1. Throughput 2. Rework Rate 3. Effect on Placement Accuracy 4. Cost (cheaper or more expensive in the long term?)

Has anyone compared the above. Please help me.

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jarnopy

#2840

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 3 October, 2000

Hi This is what i think: 1. Screen printing is fast and dispenser is quite slow 2. Quality is poor on screen printing. Quality is very good on dispenser (dispenser must have screw+pressure function). 3. Screenprinter (automatic) and dispenser (automatic) get from the same price. I like dispenser because it has very good quality and it's easy to use.

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aaronho

#2841

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 3 October, 2000

Screen printing has much lower profile than dispensing. So it is suitable for chips without body stand-off, (Even sot23 has stand-off). But is is much faster. Dispensers can not catch up with some chip shooters.

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jarnopy

#2842

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 3 October, 2000

Hi, You are right, but if you don't have very fast ship shooter then i think that dispenser is better. I have experience on both variation. If you have a line dispenser then speed is quite good. Most often it is sufficient. And unfortunate often quality is not good if you use screen printing.

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#2843

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 3 October, 2000

1. Throughput * Dispenser: Slower, may loose 70% of tact on fast chip shooters * Printer: Can be put in front of and use fast chip shooters effectively

2. Rework Rate ???? Deposition control???? * Dispenser - High control over amount paste - Coplaniarilty issues controllable - Paste rheology does not play a large role in dispensing - Requires process control to prevent missing dots * Printer - Difficult to control amount of paste - Stepped stencils can be a nightmare - Stencil apertures clog with paste - Coplaniarity issues make printing difficult - Rheology requires constant working of paste - Requires process control to prevent misprints, clogged apertures

3. Effect on Placement Accuracy

Dispensers with an accuracy of � 50�m and average speeds of 30,000 - 35,000 dots per hour are common today.

4. Cost (cheaper or more expensive in the long term?)

Price comparison points are: * Dreamsniper spoke about a cost comparison between printers and dispensers in a recent SMTnet thread (How to convince management on buying Equipment ? ---For Dave F, Wolfgang, Moonman and the rests!!! - 08:50:51 09/27/2000). As I recall, the Dreamster�s 5 year comparison preferred dispensers in that analysis. * It�s difficult to properly select model of printer and a dispenser that compare. * It may be that the decision is strategic and a cost comparison is irrelevant. * It is very easy to load a dispenser to capacity. So, shouldn�t a 5 year NPV analysis include adding a printer or a second dispenser?

In your assessment, have you evaluated: * Material waste. * Operator concerns. * Flexibility. * Material handling. * Change-over time between products. * Change over time between materials. * Material cost. * New or revised product start-up. * Specialized knowledge.

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Fraser

#2844

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 12 October, 2000

Dave,

Why on earth would you want to use a stepped glue stencil?. If you print slightly off contact the hight of your glue deposition will be roughly half the width of your adhesive aperture width so if you want a 10mil high deposit use a 20 mil aperture. If the quality of your printed glue is variable then you are doing something wrong - albeit that it is difficult to clean some stencils. As far as cost goes - don't most people have a screen printer already? - a dispenser is an additional expense - the real question is - is a dispenser worth the extra expense. I am sure I could make you a stencil for any occasion.

Cheers

Fraser

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#2845

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 12 October, 2000

Fraser: You're correct!!! We did our analysis on paste rather than glue and I missed that when changed things to respond.

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Dreamsniper

#2846

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 12 October, 2000

Hi Guys, I'd like to share this to all of you...you can start playing with the rests...Stated prices, if not indicated, are in Aussie $ or Singapore $.

Stencil Printing Adhesive

Pros

a) Less Capital Equipment Cost (Short Term).

In reality it is far more costly in the long term (min. 3 years) compare to acquiring a dispensing machine when all the Materials (Stencils, Cleaning Materials etc.), Extra Labour, Wastage, Rework Cost etc. are calculated.

b) Less Manufacturing Space.

Using a screen printer for adhesive deposition also enables increased equipment utilisation. No longer does a Solder Paste Printer sit idle waiting for a dispensing machine to complete its task.

c) High Throughput.

Do you really need the above benefit? With Stencil Printing Adhesive, an average tact time of 10 to 15 secs. per board which is roughly 4 to 6 PCB�s per minute against 1 PCB per 4 minutes on Component Placement. This speed is beneficial only with High-end High Speed Chip-shooters.

Cons

a) The chemicals used to clean stencils are generally considered hazardous material (acetone, xylol, etc), this adds a safety concern to manual cleaning. In addition, the safety and prevention of exposure to solvents are paramount to the operator staff. Frequent Stencil Cleaning is required (every 2 � 3 hrs.) to avoid aperture clogging. Manual Cleaning of Adhesive from Stencil is totally �not acceptable�.

- Adhesive Cleaner @ $95.00 / 1 pkt. Of 100 pre-saturated clothe. (Usage of 6 to 8 clothe/cleaning) Or a spray and wipe cleaner @ $80.00 / solution with 200 pcs. Of lint free clothe. - Cleaning Time of 30 mins @ $20.00 / Hr at an interval of 3 hrs. (Manual Cleaning). - Possible Installation of Exhaust for clearing Fumes @ $5,000.00 Est. Material and Labour Cost. - Stencil Cleaner costs between US$12,800 to US$40,000.00 excluding cleaning agent/solutions. Cleaning Time 2 to 3 mins. per stencil.

b) Stencil Cost @ $850.00 per stencil (Laser Cut). Whenever there�s a problem in design layout, stencil is affected and needs to be replaced. Whenever there are new products or revisions that affect PCB layout, the more stencil costs we have to spend. This is not the case with Adhesive Dispensing Machine.

c) Material Wastage. Epoxy is hydroscopic. Unnecessary exposure to the atmosphere can cause problems in reflow and will require process exposure evaluation. Adhesive stencil life is between 3 to 4 hours only. Exposed material should never be "recycled". This increases waste and adds cost to our process.

d) The stencil thickness determines deposition volumes and can not be altered. This limits the range of components (stand-off height) which can be reliably glued with a stencil. (not an issue if chips only).

e) Release characteristics of epoxy differ from solder paste. Aperture dimensions and shape must be considered. The smaller the aperture, the greater the difficulty in release.

f) Longer Set-up time against dispensing equipment when using a semi-auto printer.

g) Higher rework rate compare with using a Dispensing Machine. If there is insufficient volume of deposition, the component will skew or detach during placement and processing. If there is too much volume, the adhesive will intrude on the land patterns, causing opens and increasing cost through rework and wastage.

h) Possibility of Solder Paste contamination during the process if the stencil printer was not properly cleaned. This is if manual cleaning is the chosen method rather than getting a stencil cleaner. With a stencil cleaner, is it right to use the same solutions/cleaning agent that have been used in cleaning stencil adhesive or do you need to replace it for solder paste cleaning ? This you need to ask from supplier.

i) Need constant working of paste printer to avoid aperture clogging. Adhesive stencil life is 4 hrs. in a good environment...3 hrs. is average.

j) The more the products with bottomside components for adhesive printing, the higher the ongoing costs (eg. Consumption etc.).

Adhesive Dispensing Machine

Pros

a) Less Cleaning Required and cleaning cost is remarkably cheaper than stencil printing. b) Flexibility. Can handle various standoff height and adhesive dispensing volume can be controlled. c) Less Adhesive Wastage. d) No need for exhaust installation to extract cleaning solution fumes. e) Quicker to set-up than semi-auto stencil printer. f) Less rework rate.

Cons

a) Initially Costly. Between $85,000 (second hand) to $150,000.00 (Brand New). b) Slower than Stencil printing but this depends on how fast the line is.

Dreamsniper

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#2847

Re: Adhesive Dispenser Vs. Screen Printing Adhesives Pros and Cons | 13 October, 2000

You can achieve a wide range of dot heights when stencil printing by using a polyimide stencil along with a .040 snapoff. Loctite has a system for this that they call Varidot, by varying the size of the apertures in combination with the .040 snapoff you can get dot sizes and heights for anything between an 0402 and a large SOIC. Though Loctite has backed off from the production of these stencils due to leadtimes (they are made at their Ireland facility), you can do the same thing with the polyimide stencils from K&J marketing in Canada. The technique and process is well proven, you can find more info at:

http://www.chemical.felpro.com/electronics/tp_multipoint.html

http://www.loctite-europe.com/wwdh/us/i183ch11.htm

http://www.loctite-europe.com/eu/PDF/Brochures/asei-VARIDOT.pdf

http://www.kjmarketing.com

Mike McMonagle Senior SMT Engineer Telxon Corporation www.telxon.com

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