ISO 9001:2008 (part 5)
For a manufacturer calibrations are a critical aspect of the ISO system. A calibrated device helps ensure consistency with the product. What needs to be calibrated? A device or tool that is used to qualify the process or product. What standard should be used? Calibrations must meet NIST standards. NIST is short for National Institute of Standards and Technology which is an agency of the US department of commerce. Why do we need to meet NIST standards? The standards are a base line for measuring standards. A device calibrated to the NIST standards is considered consistent with other devices calibrated to the same standard. A micrometer at company A provides the same measured result as the micrometer at company B. Who can certify to NIST standards? NIST provides calibration services. There are also a multitude of laboratories and calibration services certified to NIST standards.
Does everything need to be calibrated? No. Its doesn’t hurt to have everything calibrated. But this would be an extra added expense that adds cost where its not really necessary. For example, you can calibrate a pressure gage on an etcher. However, most manufacturers measure the product as it comes off the line periodically with a calibrated scope. The pressure gage is typically marked for reference only. As copper is etched the bath changes and the rate of etching is changed. An automated replenishment system measures the pH and adds fresh etch chemistry on demand. The density of copper is also measured periodically but changes as the bath is used. As copper is etched the density increases. As etch chemistry is added the density decreases. The pH and density affect the etch rate. Knowing that these are moving targets the etch rate is typically controlled by line speed, the rate the process panel moves through the bath.
Measuring the line width with a calibrated scope in multiple locations on the product ensures the line is operating properly as the line is used. Constant pressure does not ensure consistent etching. Controlling the pressure gages is not entirely necessary since the product is qualified with a calibrated scope. Etched panels are also 100% inspected by Automatic Optical Inspection (AOI) equipment by most manufacturers. The point is, yes you can calibrate the pressure gage but since the product is qualified by calibrated devices its not really needed.
Most manufacturers have in-house standards that they have calibrated to NIST standards by a calibration service. In order to maintain a level of cost control this is a good idea. For example, an inspector drops their micrometer on the floor. It seems to work. To verify that it is still working properly you need to verify its accuracy by verifying calibration. Micrometers are calibrated by measuring various thickness metal gage blocks repeatedly. Having an in-house set of NIST certified gage blocks is a good idea. Verifying calibration is an easy task. If you don’t own a set then you need to send the micrometer out to have it verified by a calibration service. If the micrometer is used without verifying the calibration then you run the risk of a non-conformance getting by the inspection process. With this in mind its cheaper to have a set of calibrated gage blocks on hand.
When auditing a vendor ask to see their calibration records. If calibrations were performed by an outside service ask to see the calibration certificate provided by the service company. A legitimate certificate shall be provided with a raised seal. If they do their own in-house calibrations ask them to calibrate something. Have them go through the motions and observe them in action. When walking the manufacturing area look for devices or gages that can potentially by used on the product. Make sure they have a calibration label or for reference only label on the device. If there is no label point it out and ask how the product is qualified. Auditing an ISO certified company is less critical than auditing a non-ISO certified company. Non-ISO certified companies tend to fall short when it comes to calibrated devices. If you are ISO certified and your vendor is not, then its your responsibility to make sure they are in control.