Monday, April 30, 2012

Concentration, NVR Testing & R.O.S.E. Testing...What does it all mean to me?

Concentration Readings, NVR Testing & R.O.S.E. Testing...What does it all mean to me?

By Tim Noble

A common topic of discussion is bath management in a PCB defluxing process.  How does one ensure that heir wash solution is in its optimal cleanng state? 

Cleaning systems, i.e. the Aqueous Technologies Trident, come with bath replenishment reminders built in with defaults of 100 cycles, but this is a very generic figure.  It largely depends on what you are cleaning and how quickly the soil you are cleaning will degrade the cleaning capabilty of your wash solution.

When managing your wash solution there are three characteristics that need to be monitored:

  • Concentration
  • Soil Load
  • Cleaning Effectiveness

Concentration is typically measured with a refractometer in many chemistries, and will tell you the concentration of chemistry solution to DI water in an aqueous cleaning solution.  This figure is given on a Brox scale and needs to be converted to concentration by referring to the datasheet for the specific cleaning product.

Soil load testing measures the amounts of soils that are building up in your wash solution tank.  As the wash solution further loaded with soils, the less effective it becomes at cleaning.  This testing method collects samples at intervals and allows you to properly analyze the soil loading of your bath wash solution.  (Please refer to our article on NVR testing.)

Lastly, you need to collect data that will allow you to identify how the oncentration and the soil loading are impacting the cleanliness of your PCBs, so you will need quantifiable cleanliness data on your PCBs.  The easiest way to collect this is via R.O.S.E. (Resistivity Of Solvent Extract) testing.

My recommendations would be to assemble a matrix of Data including the folowing columns:
  • Cycle Number
  • Concentration Reading
  • NVR Test Result
  • R.O.S.E. Test Result
  • Trident (Resisitivity Reading) - If Applicable

I would taking readings at various intervals; i.e. 0 (Control), 20, 40, 60, 80, 100, 120, etc.) at least until you witness a degradation in the cleaning results.  I would assess the data to establish a reliablebath replenishment point.  I would ensure to leave a bit of cushion, for example, if my bath were to degrade at 120 cylces I would leave a 10-20 cycle cushion and set the machine reminder to about 100.

You will notice that I have also tracked the Trident Resistivity reading, and even though this is NOT to be confused with a cleanliness tester, it CAN be valuable as an indicator if something in your process is off.  You possibly can identify a correlation between the other data points and the resistivity reading.

Hopefully thi iformation helps you to manage your bath solution and remember, there is no one specific figure that gurantees success.  You need to monitor multiple figures to ensure that your chemistry is working at peak performance.

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