Archive for category Reading Profiles
Total Heat – Another way to analyze your thermal profile
Posted by Paul Austen in Extracting Parameters, M.O.L.E. MAP, Reading Profiles, Reflow Profiling, Thermal Profiling on January 21st, 2011
One of the most popular ways to determine if a thermal profile of an electronic assembly is within specification is to consider the limits placed on four measurements or parameters: Initial Ramp Slope, Soak time, Time Above Liquidus and Peak temperature. Keep these four parameters within the specified (solder paste) limits and you can be assured that you are soldering the parts without damaging them.
Figure 1 Typical thermal profile with the four traditional parameters within spec
There are other ways to look at a profile which can be helpful in determining if the profile may threaten components and showing if it is consistent, both across solder joints, and over time.
In the profile example above, the Time Above Liquidus (TAL)on solder joints 1 and 3 are within 2 seconds, yet channel 3 (from the data; plot not shown for visual clarity) had more readings at higher temperatures. This means that although this part may have the same time above 183ºC, more readings were at temperatures higher than channel 1; higher risk of damage. Also note that the peak temperatures were not far apart; 222.2ºC vs. 223.5ºC.
So we added a new measurement to the MAP software to not only show Time Above Liquidus, but also consider the temperature values during the TAL portion of the profile. This new measurement has several names: “Total Heat,” ” Area Under the Curve,” or “Stress Integral.” It combines the time element of Time Above Liquidus with the temperature measurements during that time to give the Total Heat the component experienced, expressed in degree-seconds.
Figure 2 Total Heat measurements (component 1 only shown for clarity)
In this case, even though the Time Above Liquidus values are within 2 seconds and the peak temperature is less than 2 degrees apart, the Total Heat values are 2278º-sec and 2628 º-sec which differ by 350 º-sec! This clearly points out that component 3 had to withstand more Total Heat than component 1 and this simple parameter can now be examined in an instant, using the latest; version 2.18j of MAP software.
The Fastest Way to Know Your profile is “OK”
Posted by Paul Austen in Extracting Parameters, M.O.L.E. MAP, Reading Profiles, Reflow Profiling, Thermal Profiler, Thermal Profiling on February 25th, 2010
Now there is a way to verify that your profile requirements are being met in less time than you ever thought possible. The letters in the name M.O.L.E.® thermal profiler have always stood for Multi-channel Occurrent Logger Evaluator. Now the patented* “OK button” feature truly makes “E” in MOLE a reality, because now the MOLE profiler can automatically compare the measured temperature profile to your pre-programmed profile requirements.
The ECD V-MOLE with patented one button “OK” profile evaluation
(The OK Button is also available on the 20-channel MEGAM.O.L.E.™ thermal profiler, and OvenCHECKER™ )
Taking only seconds, the MOLE can tell you and your oven operators if the profile just measured is in or out of specification with the universally understood Green for good (GO!) or Red for bad (STOP!).
You get to set the specification limits for any or all of the four most popular profile parameters:
- Ramp Slope
- Time Between temperatures
- Time above Liquidous
- Peak Temperature
…and you can choose which of the MOLE’s input channels to include, up to 20 channels on the MEGAM.O.L.E.™, and three on the V-M.O.L.E.™ thermal profilers.
The Specification Table in MAP Software
Using the MAP™ Profiling software, enter your specification limits for the four profile parameters in the Upper and Lower Limits table in the “Target-10 OK” tab. These values will automatically be sent to the MOLE profiler when you use the Verify Process Wizard to confirm that a previously characterized oven recipe is still performing within specification.
MAP™ Profiling Software Target-10 OK Profile tab
Once programmed, the MOLE profiler can be used many times (up to 96 times) to Verify your oven is producing the same profile, without reconnecting to your computer. Simply run the profile and press the “OK Button” on the MOLE. No more running back to the PC software to download to see the results. One push of the OK button, and you get your answer…Go, or No-Go. It’s that simple!
*U.S. Patent Number 7653502.
When is a Profile Not a Profile?
Posted by Paul Austen in Reading Profiles on June 11th, 2009
I hear this all the time, “We only have three profiles used on our production floor.” Just what does that mean? For some it may mean, “We only have three different oven settings used on our production floor.” For others it may mean, “We only have three different kinds of solder paste used on our production floor.”
Let’s get our terms straight and put some definition to a few key words used here:
Profile – The graphical plot of temperature as a function of time, as measured by one or more thermocouples at points of interest on a PCB
Profiling – Act of gathering the temperature as a function of time data using profiling instruments
Recipe – Oven settings required to produce the desired profile
Zone temperature settings (Set points),
Conveyor speed setting
Convection rate or flow settings
Etc
As a matter of fact, given a specific solder paste, there is only ONE profile you need to worry about- the one needed by that paste to properly heat the solder paste to make a good metallic bond between components and the substrate (typically plated pads on a PCB), and that does not cause damage to the components. However, depending on the characteristics of each oven (I.e. number of zones, convection rate, conveyor speed, etc) and the thermal nature of the assembly (I.e. its component density, board thickness, etc), there will be different oven recipes needed to make that single profile happen. In other words, different ovens will require different recipes to produce the same profile on a given assembly. Or, different assemblies will require different recipes in a given oven. So if you are soldering many different assemblies in a variety of ovens, you will have many oven recipes on the factory floor, even though you are trying to achieve only ONE profile, this is because you are using the same solder paste on all assemblies.
In the profile graph above, BOTH the Profile and oven Recipe needed to make the profile happen on this assembly are illustrated.
The oven Recipe needed to produce the correct thermal Profile on an assembly is NOT the same thing as a Profile. Or, a Profile is not a Profile, when it is a Recipe. Don’t be fooled when you hear, “We only have three profiles used on our production floor.” Find out exactly what is meant by this.
And remember, Profiling the assembly in the oven in order to fine tune the Recipe which will solder the assembly to meet the Profile needs of the solder paste (and not damage components) is a vital step toward a good thermal quality management program.
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