A good Thermal Quality Program (ThQM) demands consistent oven verification to show that the reflow oven is reproducing the same thermal environment as it has in the past. The OvenRIDER is a good way to verify oven performance. How do you make best use of these tools, both the OvenRIDER pallet and the OvenRIDER SPC (ORSPC) software?
There are five basic steps:
Let's get right into it:
Set up the Oven, Workbook and M.O.L.E.®
- Place a magnet at the beginning of zone one. The OvenRIDER came with at least three magnets. This is not because we think you only have three zones, but because we figure you may have more then one oven, and you only need one magnet per oven to mark the start of zone one and let the OvenRIDER measure conveyor speed for you. The software detects this magnet in the profile and uses it automatically place the start of the oven model on the profile's time axis. It does not matter where you put this magnet as long as it is on or before the beginning of zone one. You can even put it outside of the oven so it can be removed when you are not using OvenRIDER. Just be sure you always put it back in the exact same spot.
- Set the oven’s recipe you plan to use for this OvenRIDER run. It can be the same recipe you are now using to solder boards. In fact, you may want to start an OvenRIDER collection of runs for all your different recipes. This does need to be a big one time effort for all your recipes. You can do this slowly for each recipe one at a time as you do line change over. In time you will have enough runs for each recipe to begin useful oven Verification.
- Start the OvenRIDER software and select the Workbook you wish to save these recipe runs. If this is the first time you opened the software, a sample work book will be opened. Go to the file menu and close this Workbook. Then open the file menu and start a New Workbook or open an existing Workbook you previously created. The Workbooks can help you group like OvenRIDER runs. Having a work book for each oven recipe is the best for Oven Verification. You can name Workbook the same as the recipe name to help keep it straight.
- To make sure the M.O.L.E.® is ready, connect it to the PC via the communication cable and run the Configuration Wizard in the OvenRIDER menu. This will find the M.O.L.E.® and set it's clock and other settings.
- Load the MOLE into the OvenRIDER barrier and connect the configuration plug
- Make sure the oven is up to temperature and ready to receive product. Also make sure the conveyor width is set the OvenRIDER’s width.
- Start the MOLE, close and lock the lid, and load the OvenRIDER pallet onto the oven conveyor.
- When it gets through the oven, open the barrier and stop the M.O.L.E.® by pressing and HOLDING the button until the Status LED turns off by itself.
Model the oven
Oven modeling is critical. This tells the software how big each oven zone is and where each zone is on the thermal profile so it can correctly show which zone had what effect on that portion of the profile.
Above is a typical Oven RIDER thermal profile with an oven model (vertical dashed lines) in place. Each zone influenced the “shape” of the thermal profile of the OvenRIDER’s sensors as it passed through oven. The amount of influence depends on the oven recipe temperature set point for each zone, the conveyor speed and the convection rate (fan or air speed). The temperature set points and conveyor speed has a straight forward and expected effect. The convection rate is a little different. Some ovens allow this to be changed and may be measured in several ways like: velocity, pressure, percent, Hz or RPMs. In some ovens, the convection rate is not adjustable or has two or three settings like: Low, Medium, and High. In either case, convection rate changes are one of the leading causes of profile changes when neither the conveyor speed nor zone temperature set points have been altered. So understanding what part of the profile each zone influenced is critical to pin pointing where problems in the oven have occurred.
Here is the best way to model an oven, any oven:
- After the profile run, connect the M.O.L.E.® to the PC via the communication cable and press the Read OvenRIDER button.
- The software will as you how much data you want to use from the previous run, if there is a previous run. This time, the first time don’t select anything by un-checking all three.
- The OvenRIDER profile will look something like the profile below. Because you installed a magnet, the start of zone 1 is in place on the profile, and that’s it. It is ready to Model the oven.
- Start the Manual Zone Definition by selecting it on the Manual Zone menu.
- Select the number of zones check boxes on the let that your oven has. Name them if you like. Leave the values it defaults for Zone Lengths and Units. We will take care of that next. Note it has the measured conveyor speed already calculated and entered in as the conveyor speed value.
- Enter the Zone Temperature Set Points in the Top column. Note the Bottom values copy from the Top values as you enter them since most oven use the same Top and Bottom values. Enter the bottom values, if different, after you enter the Top values. When done, click OK.
- You will now see all of your zone boundaries located in the default locations, but not in the right locations. Note the small boxes at the top of each boundary. This is a handle for you to grab and move the boundaries to the right locations. The right locations are in that little dip that happens between zones you can see in the Ambient sensors, the Red, Blue, and Green profile lines (Channels 1, 2, and 3). So start moving the zone boundaries into place. Remember, don’t move the start of the first zone, this was set for you by the software when it detected of the magnet.
- Your profile and oven model should look like mine below. This is the “thermal” Model of your oven. It’s already saved with this profile, but let’s save it for future use with other recipes used in this same oven.
- Go to the Manual Zones menu and select Setup Zones.
- This will re-open the Oven Zone Setup dialog box. Hit the save button and name your oven model. I recommend using the Oven or line name. This model can be used for other OvenRIDER profile runs using the same model of oven, but with different oven recipes later on. Use the Load button to recall this oven model on future runs.
Collect a base set of OvenRIDER runs
You now have a good oven model and your first run at this recipe. You need to collect at least three runs at this same recipe before enough data is collected to meaningful, statistically. This can be all at once, but this take a big chunk of time from production, and most don’t have that kind of time. I recommend you take an OvenRIDER run at the beginning of each day or shift, while you are running the same recipe, for several days. You will have 3 or more runs in less then a week
If you don’t run the same recipe for more then a day, you can set an “Oven RIDER Recipe” near the recipe setting you use most often. Start the day with that recipe, take the run, and then move to the “real” recipe you plan to use that day.
If you want to do three or more OvenRIDER runs all at once, just be sure to cool the M.O.L.E.® and the Pallet to room temperature between runs. Do NOT short cut this critical cooling process. This will save the M.O.L.E.® from possible over heating and assure the pallet temperatures are consistent run to run. 20 minutes on a nice fan will be enough in most situations.
Once you have several runs, you Spreadsheet will look something like this:
Make use of the user columns, the Green ones. This is where your can name the column anything you like. At least make a column for Recipe, and maybe the Machine or line name. I also have a Part Number column to identify the part or assembly soldered using this recipe.
Set the spec limits
With a good set of OvenRIDER runs collected under the same oven recipe, at least three, but five or even 10 is better, you can now set limits on the average of these runs. Do the following:
- Select the Spreadsheet tab and filter out or “hide” the runs that are NOT part of the base OvenRIDER runs. If you named each base run like I did in the example, this is easy. Select the filter dropdown arrow in row 4 of the column where you named the base runs, n my case column E, and select the name that you used to name the base runs. I used “Base Runs,” for simplicity. This hides (temporally) all the other runs. If you don’t have any other runs yet, then you don’t need to do this. The statistical data at the bottom of each column is now calculated only from those runs still visible.
- Now select the Admin tab and click the drop down arrows in the LSL and USL columns. Select the -10% and + 10%. This will set as upper and lower spec limits +/- 10% of the Average values for your base line runs showing on the Spreadsheet tab for ALL the values OvenRIDER measures. These will be good starting values to see how your oven is doing.
- Optional – You may want to select +/- 5% later on after you have a few more runs, if you wish to run tighter specs. Or, you may want to change the conveyor speed spec limits to a little tighter because you know you machine can do better then 5% or 10%. Finally you may want to remove some of the specs because you are not concerned with those measured values. To start with, it will not hurt to keep all the values.
Monitor of verification
Now each time you run the OvenRIDER at this recipe, you can see in a flash if the ALL of the measured values are within the specs you set. Simply select the OvenRIDER Data tab and give the values a look.
If any of them are Red (above spec) or Blue (below spec), then there may be a problem in this portion of the oven. The values of most concern are the Average Temperatures and Process Delta per zone. If these begin to fall out of spec, then you know there may be a problem in that zones ability to heat.
All black, as in this run, the oven is ready to roll.
Any parameter out of spec should be examined to see if it’s a concern or not.
If you wish to get deeper in the SPC control you can create. Xbar-R Charts for any of these values as well. Simply drag and drop any measured value in the column to the left into one of the SPC A, B, C… boxes. Check the box to add that SPC group of charts to the tabs pages below.
Select the tab to see the X-bar R charts. Here are many production runs of the oven ruder captured of time.
These chart use all the typical SPC rules to determine process control.