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Pasting ahead

Views: 3317

Pasting ahead - Nov 04, 2006 by Bill  

Pasting ahead - Nov 06, 2006 by

Pasting ahead - Nov 06, 2006 by

Pasting ahead - Nov 06, 2006 by Steve Thomas  

Pasting ahead - Nov 06, 2006 by nodlac  

Pasting ahead - Nov 06, 2006 by Stephen  

Pasting ahead - Nov 11, 2006 by

Pasting ahead - Nov 12, 2006 by

Pasting ahead - Nov 13, 2006 by

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Pasting ahead - Nov 13, 2006 by patf  

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#44878

Pasting ahead | 4 November, 2006

Hi all,

What are the pro's and cons of pasting ahead? The definition of pasting ahead for this question is the act of pasting 10 or 15 pc boards and then running then repeat. I do not like this philosophy. I'd prefer to paste, run, reflow then repeat. This eliminates the amount of time between paste application and the pc's entrance into reflow. The fresher the paste the better the solder joint. My dilema here is upper management wants the two lines to share one stencil printer thus saving the cost of purchasing a second printer. They propose to paste ahead, allow second runner to change stencils, paste their pc's, and so on. If shifts end approaches, they offer to store the pasted pc boards in a refridgerator overnight until population the next day. Help!! Does anyone out there find this to be a bit odd? Where could I find articles or documentation frowning upon pasting ahead? If I had something written by an "expert" maybe management would leave me alone and simply purchase a second stencil printer. Thanks for any suggestions you have.

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aj

#44893

Pasting ahead | 6 November, 2006

Bill,

I thought I had it bad here!!!!

I am sure if you contact your Paste Supplier they will give you all the advise you need. Better still contact a Printer Supplier and tell him to assist you in justifying the purchase of a new printer.(I am sure he would be more than happy!).

From my point of view you would be running totally inefficiently for a start not to mention the fact that any one of the Placement machines could breakdown at anytime.

I am sure if you carried out a cost analysis on Operator Changeover and Machine downtime waiting on boards along with Product Turnaround you will easily justify a new printer.( you can pick up printers quite cheaply).

If all that fails I would write a note on a letter and say "Aurevoir" and get the hell out of there.....

aj...

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SWAG

#44896

Pasting ahead | 6 November, 2006

I don't know of any articles but you will see the following problems:

The flux will evaporate from the paste and your solder joint will look very grainy or will not reflow at all.

The paste will not have a good, tacky quality. Your pick and place or chipshooter will place small parts and they will move easily or not even get placed at all as they will stay with the nozzles instead of sticking to the paste deposit.

The results are hard to predict or put time limits on because there are too many variables such as stencil life of paste, humidity, etc.

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#44897

Pasting ahead | 6 November, 2006

Will they give you the opportunity to develop a DOE to look at quality vs. print life? It probably depends on the kind of placement equipment you have, but with our chipshooters we always had missing/misplaced parts if we populated dried out boards.

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#44906

Pasting ahead | 6 November, 2006

Checks calendar ...nope not April 1st.

-The fresher the paste the better the solder joint. Agreed

- My dilema here is upper management wants the two lines to share one stencil printer thus saving the cost of purchasing a second printer. They propose to paste ahead, allow second runner to change stencils, paste their pc's, and so on. Is/are management process engineers savvy in the SMT process?? If so then they must know a little bit on failure analysis.

- If shifts end approaches, they offer to store the pasted pc boards in a refridgerator overnight until population the next day. Only if you can guarantee the refridge is plumbed with nitrogen (or inert atmosphere) as most refridges are not oxygen free that contributes to oxidation and they have a high degree of moisture..not good for reflow as can cause a popcorn type situation. Not to mention contamination left behind from yesterdays Chinese food. That General�s Chicken is hell on PCB�s

- Help!! Does anyone out there find this to be a bit odd? Very very Odd

- Where could I find articles or documentation frowning upon pasting ahead? If you are running standards then IPC J-STD-004 may help.

- If I had something written by an "expert" maybe management would leave me alone and simply purchase a second stencil printer. http://www.smtinfocus.com/processguide_printing.html#Environment Quick this site goes away Nov 15th. bummer

And

http://www.loctite.com/int_henkel/loctite/binarydata/pdf/elec_Step_by_Step_Soldering_0801.pdf
A Snippet from Loctite�s Link above:
Use of solders with the correct rheological characteristic can eliminate such defects. Environmental variables such as temperature and humidity can affect the rheological characteristics of a solder paste. Solder pastes must be formulated to print satisfactorily across a wide range of environmental
conditions, as maintaining a constant environment on the production floor is not always possible. Many electronic manufacturers have multiple locations with varying conditions in their production environment�further on... The ability of a solder paste to print acceptably after a delay in production is critical to reducing
defects on the modern production line. A paste�s �abandon time� is defined as the maximum amount of time between two printing cycles that will provide acceptable results without reconditioning or kneading the solder paste or cleaning the stencil. Printer downtime is typically due to placement
problems or operator breaks. Solder pastes with long abandon times reduce printer maintenance and solder defects due to paste drying, and improve subsequent processes in the line. Evaluating abandon time is very subjective as the definition of acceptable printing can vary greatly.

Hope this helps and good luck...Mr. Solder paster refridgerator saver guy ... Candiadte for Budweisers Real American Hero Contest http://www.neonowl.net/budlight/
Sorry for the lil joke hopefuly no offense (offence?) is taken...all in good fun.

Seriously looking over the loctite site will help plenty.

Enjoy,
Cal

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#44910

Pasting ahead | 6 November, 2006

Look on the bright side you will only have to store pasted boards overnight in the fridge, one time.

Just make sure you reflow one such board before you waste time populating any others.

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KEN

#45002

Pasting ahead | 11 November, 2006

Ever notice what happens to a cold drink when you take it out of the cold fridge and let it sit at room temp. It "sweats". I don't think you want moisture dewing on your circuit boards.

I think your managers should stick to managing. Leave the process stuff to the experts.

Like I always say. Just because you can do it doesn't mean you should do it.

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Thomas

#45003

Pasting ahead | 12 November, 2006

One printer 2 smt lines = No problem, but then you will need 2 ovens.
It is even sometimes a more valuable cost savings depending on what production you are into.

At first the stencil printer with a divertion conveyor, then straight ahead into the 1 assy line, meanwhile you are setting up the next job in the second line or the secondary side of the product. A fast stencil printer will keep up with the production in 2 lines (assuming that you are not producing cell phones or simular). The drawback is that you need 2 ovens.
We have this scenario with the DEK stencil printer and 2 smt-lines of NEXT machines and also a diverter at the end, feeding 2 ovens.
Then we have a second line for prototype and NPI production only.
You must do your math depending on how your production looks like. If your mangement goes for the key-numbers, meaning that the OEE and product changeover time is critical, maybe this is the best for that particulary solution.

But Never Ever store paste printed pcb:s into a fridge. That is totally outrages!

There are a numerius way of how to produce the boards throughout the smt-lines, but only one way to do it correct, according to the specified needs.

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guess

#45007

Pasting ahead | 13 November, 2006

I suggest to review your board , do both boards have fine pitch QFP's or TSSOP's? . If yes, best approach is to finish board at a time to ensure best quality . You can refer to your solder paste TDS to justify why you choose this approach.
If one of the board dont have fine pitch you can do manual print. You can use PCB break away as stopper . One operator do the squeege action, while other secure the alignment by holding the stencil frame ,old school but effective. If this is not allowed, you can design simple manual printer using simple backyard tools like C clamp and bearing. When I was in the manufacturing,I made one and proven to be effective .

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#45016

Pasting ahead | 13 November, 2006

Bill,

We only allow 3 boards to be printed in front of the pick and place equipment. It is important to keep the abandon time to a minimum.

You did not mention the paste that you use. Do you use no-clean or water soluble? Do you use lead free?

Solder paste is hygroscopic which means it will absorb or expel moisture. Moisture can cause problems such as slumping, solder balls, splatter, and component popcorning. If your environment is too dry you paste will expel moisture (dry out). This will cause other soldering issues.


Pat

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TM

#45025

Pasting ahead | 13 November, 2006

SIPAD - Check them out. Used them at a previous company.

www.sipad.net

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