A question was posted on Circuitnet (May 18, 2009) asking if there is a standard test board that can be used for profiling/calibration of a reflow oven. Answers were provided by profiling companies, oven and rework station manufacturers.
The consensus from all groups was:
- There is no standard test board.
- There is no substitute to creating an actual profile of your product.
Here is a summary of panelist replies, including from yours truly (for a full transcript go to http://www.circuitnet.com/articles/article_59131.shtml).
Brian O’Leary – KIC (full version)
The short answer to your question is no. There is no industry standard test board.
Test boards, also sometimes called “golden boards,” are an imperfect measure. Often, they are used for calibration purposes, but keep in mind every time you run the same PCB through an oven, some mass of the board is lost. For this reason, a true GOLD standard that is identical to your production board is difficult to achieve, unless you can somehow recreate the exact same conditions each and every time you profile your standard test board.
Since PCBs lose mass, some manufacturers will create calibration tools out of plates of stainless steal and use metal slugs to simulate components. Of course, a hunk of metal is no closer to a production board than a golden board, but at least it gives you a relative measure that is repeatable.
So what is the best answer if there is no perfect tool? There is no better representation of what is going on with your Reflow process than running an actual profile of a production board. The good news is that there are tools available that do not necessarily mean running a profile equals destruction of a sellable product nor does it mean that you need to waste the next few hours profiling.
Both oven manufacturers and profiling companies have developed onboard databases that allow you to develop in-spec profiles before you even profile (see this link) so when you run a verification profile you can at least do so knowing that the PCB being used can still be sold!
Another method of ensuring your process is continuously in spec and can serve as an early warning if things are going astray is the use of systems designed to monitor your oven.
For example, KIC’s 24-7 and Vision will create virtual representations of your PCB all based off of a true “golden board,” since the PCBs used to set up the system to create these virtual profiles are run through your process as actual profiles. As an added bonus, these same boards do not suffer from the repeated use problem described above with golden boards.
Fred Dimock – BTU
Oven manufacturers normally use custom designed test fixtures to simulate a board but their real purpose is to measure uniformity across the oven and confirm that the oven is working correctly. The test board might match a small percentage of boards actually being produced but is not close to many more and is not intended for calibration.
….I have personally seen companies place unrealistic performance specifications on reflow oven testing with boards that have little to do with actual production needs. For example, we once were required to show that an oven could reproduce an inspect ramp soak spike profile on two 12 X 18 inch aluminum sheets that were 0.040 and 0.080 inches thick without changing any recipe parameters….
….From a surface mount manufacturing point of view – single board oven performance testing has little benefit. The real answers are to use actual boards with TCs placed on the critical components….
Richard Burke – Datapaq
First of all, nothing can take the place of running profiles of your actual PCB’s…..
…There is really no industry standard test board available……to suggest otherwise would be dangerous whereas this would assume that all assemblies are identical and this is not the case. If you set the oven up to the test board, it would invariably be different than your own assemblies. This is not a risk worth taking.
Al Cabral – VJ Technologies
Test boards can be created to illustrate specific characteristics of a reflow system, be it heating / cooling capacity, thermal repeatability, thermal uniformity across a conveyor system or designed to emulate a particular type of product.
It’s very difficult for one test vehicle to do it all well. A test board supplied by an oven manufacturer or independent supplier will likely address one or two of the aforementioned.
For example, a test vehicle designed to compare several ovens across multiple lines can be vastly different from a test vehicle designed to measure cross belt uniformity. Similarly, a test vehicle designed to gauge percent infrared, may not be well suited for CpK measurement.