How to Avoid Equipment Calibration Problems

It is critically important for companies that offer electronic contract manufacturing and assembly services not only use equipment that is in calibration, but also have controls in place that prevent the use of equipment that has gone out of calibration (i.e. “out of cal”).

It should be obvious that having out of cal equipment is bad for any company offering electronic manufacturing services. But in case it is not obvious to you, maybe it will after looking at an example.

Electrical Functional Testers
EMS (electronic manufacturing service) companies utilize electrical functional testers (sometimes called “EOLT” for “End of Line Tester”, or “FCT” for “Functional Tester”) that apply power to a manufactured circuit board and then take voltage and current measurements. The EOLT will flag a circuit board as bad if the measured voltages or currents are outside of the unit’s specification. If the equipment is out of calibration, then there is the chance that the measurement was done in error. A truly defective device could measure within specifications, causing a bad unit to get shipped to the customer.

Clearly, utilizing equipment that is calibrated is necessary to maintain a high level of quality.

So, how do EMS companies avoid using out of calibration equipment?

Spreadsheet method
Many EMS companies maintain a notebook or an electronic spreadsheet that contains the following information for each piece of calibrated equipment:

  • Equipment ID
  • Equipment description
  • Location of equipment on production floor
  • Date when equipment is due for calibration

The problem with this method is that it easy for someone to become lackadaisical and forget to periodically refer to this spreadsheet and look for pieces of equipment that are soon due for calibration. When a piece of equipment has a 1-year calibration cycle, it is easy to forget about it.

Schedule reminder method
Some companies use their email system to schedule a reminder when a piece of equipment is due for calibration. This is an improvement over the previous method but is still cumbersome as it requires the manual setting up of multiple email reminders for each piece of equipment. Further, if the person that setup the reminders leaves the company, there’s a possibility that these reminders won’t go out since their mailbox would have been disabled.

Passive calibration system
The two methods above are really passive in nature: a Quality Assurance (QA) person fills out a spreadsheet with equipment calibration due dates and possibly setup email reminders. The “system” then just sits idly by until the calibration due date is reached. Do you see a problem with this system?

The are several issues with a passive system like this. First of all, if an email reminder goes out on the date a piece of equipment is due for calibration, chances are that an equipment calibration company can’t come out that instant and calibrate the equipment. So, some lead time is needed.

A bigger issue is the location of the equipment. Many years ago when Futaba used spreadsheets to keep track of equipment and their calibration due dates, when equipment was due for calibration, the QA department sometimes had a difficult time locating the equipment. A lot of things can change in the time interval between calibration events. When a QA person logs a piece of equipment as being located in LOCATION A and needing calibration on mm/dd/yyyy, there is a chance that, due to changes in production requirements, the equipment could be moved to LOCATION B by the Test Engineering department or Production department without informing the QA department so the spreadsheet could be updated. Sometime this move created a big quality concern loophole…

Warning! -> Limited calibration
If an electronics assembly company is large enough and has been around long enough, they will eventually have equipment that will not completely pass calibration. You may be thinking, “What does this mean? Equipment either passes calibration or fails, right?”

Sometimes when equipment does not completely pass calibration, it is not an issue because the section of the equipment that fails calibration is a section that is not used on the production floor. For example, an EMS company may use a 4-channel oscilloscope on the production floor in the functional testing of a circuit that they manufacture for a customer, but only use one channel of the scope. They may use scope channel #1; channel #4 is defective and failed to pass calibration. The danger here is how to prevent production from using channel #4? The solution is not as easy as you may think. A company may think, “We can continue to use this limited cal oscilloscope in this area of the production floor because all the units that we test here don’t use the defective channel #4.” Well, they may not use channel #4 now but may down the road! Or, maybe the scope will be moved to a different area of the production floor where channel #4 is needed. As you can see, this opens the door to serious quality concerns.

Having detected these loopholes in the past, Futaba has in place an active calibration system instead of a passive one.

Futaba’s active calibration system
Since 2006 Futaba has been using a SQL database to control and monitor all aspects of our factory – including equipment calibration. Futaba’s equipment that requires calibration is setup in our Tracking System with their calibration due date and calibration frequency of either 6 months or 1 year. The system will automatically generate “calibration soon due” notification emails 90, 60, and 30 days out from the equipment’s calibration due date. This gives our QA department plenty of lead time to schedule a calibration company to come out.

Futaba has controls in place to prevent the use of non-calibrated equipment and prevent the use of calibrated equipment outside it its designated areas. For example, when a test operator launches our functional test program, the first thing the program does is to communicate with the test equipment and obtain ids for each piece of equipment in the test rack. The test program then communicates with the Tracking System database to verify 3 things:

  1. That the equipment is allowed to be used with the functional test program.
  2. That the equipment is allowed to be used where it is. (Helps prevent people from moving the equipment during the time interval between calibrations.)
  3. That the equipment is not out of calibration.

If you happen to get a tour of an electronics manufacturing company or an electronics assembly company, ask the employees there how they prevent equipment calibration issues like the ones mentioned above. Hopefully this document has helped you realize the possible problems EMS companies face in regards to equipment calibration and how to avoid them.