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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Paste life span on the PCB

zam_bri

#5556

Paste life span on the printer | 14 March, 2001

In my factory, we are setting the shelf life of paste on the printer to be 2hrs. What is the best way to measure this and when does the 2 hr start? It is quite difficult as sometimes the line is down for 1 hr and then start again. Should we cummulate all the down time or does it have to be a continuous 2 hrs.

I need to figure out a way to time the 2 hrs. Do give it some thought and share with me the best method.

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#5558

Paste life span on the printer | 14 March, 2001

zam,

each paste mfg. has different "stencil life" times. check w/ your paste mfg's specification for stencil life. also, temp and humidity inside the printer's chamber effects "stencil life" time. we keep ours around 20C @ 50% RH. higher temps and lower RH's dry out the paste faster. Hope this helps.

Pete

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#5561

Paste life span on the printer | 14 March, 2001

In order to track the board flow through your line you will have to hook up all conveyor input sensors as well as the last output sensor to a PLC. You can program the PLC to provide an alarm signal if a accumulative time of xxx hours for any board is exceeded. Stefan

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blnorman

#5562

Paste life span on the printer | 14 March, 2001

We just ran a study to try to determine this. We exposed the paste to 85% humidity to simulate worst case manufacturing. At various times we removed the paste from the chamber and tested it for tack, solder balling, wetting (copper coupon), and viscosity. Basically printability. We also ran 10 test boards down the line to see if there were any processing problems. We determined our paste could sit on the stencil for 3.5 hours with no detrimental effects.

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#5573

Paste life span on the printer | 14 March, 2001

6 Work Life Test

6.1 Obtain a stencil with 15 to 20 rows of a series of 0.025 by 0.050 inch apertures spaced 0.050, 0.040, 0.025, 0.015, 0.010, 0.010, 0.025, 0.040, 0.050 inches apart. See Appendix 1. Source of supply: Metal Etching Technology.

6.2 Clean (i.e., chemically or with abrasion) the tarnish from a sheet of bare copper laminate.

6.3 Using the stencil described in paragraph 6.1 above. Apply enough paste for 5 to 6 prints.

6.4 Print the paste on the laminate.

6.5 Reflow solder the laminate using the paste manufacturer�s recommended profile.

6.6 Clean the laminate with isopropyl alcohol.

6.7 Inspect the solder fillet at X10 magnification.

6.8 Describe the fillet and the location of bridging between fillets. Ideally, there should be no bridging.

6.9 Quality Assurance may elect to archive the laminate.

6.10 Record the results.

6.11 Leave the paste on the stencil for one hour.

6.12 Repeat steps 6.2 through 6.11 above.

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CAL

#5578

Paste life span on the printer | 14 March, 2001

There are also Process monitoring tools that mount directly to your blades and monitor the paste. Impedance Spectroscopy is the process monitoring theory behind the tool. It works by having good sample data logged that the monitoring tool can compare against. You can down load empf's report via the web http://www.empf.org under Order Technical Publications; Solderability Doc Number EMPF PP0016. www.aci-corp.org IS4000 Contact me for more details

Cdriscoll@aci-corp.org

Cal Sorry DAVE F. I feel like a sales man some times.

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#5601

Paste life span on the printer | 15 March, 2001

Well Cal, we all had better be sales types. [Otherwise our bosses might question our reason d'entre, eh? My good looks only carry me so far.] I think as long as the sales types are adding content there is no reason to complain.

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