Page 54


www.us- tech.com


December, 2017


Machine Optimization: Is it Artificial Intelligence? By Bjorn Dahle, President, KIC W


hether we hype it and call it artificial intelligence (AI) or the more modest “machine optimization,” reflow oven opti-


mization software is a great example of a smart machine. A reflow oven is a complex machine with PC-


controlled heaters, airflow, conveyor speed, flux management, and much more. Reflow ovens serve one main purpose: to process any product in accor- dance with its soldering specifications. More precisely, this is where three sets of


process specifications for components, solder paste and substrate intersect. The key measurement is called a product profile, which will need to fall within the relevant process specifications, also


Profiler companies then developed software


algorithms that used the laws of thermodynamics to calculate the effect of a changed processing envi- ronment. With a known starting point, namely a single profile run through the oven, the mathemat- ical model would calculate how varying tempera- tures and duration at each temperature would affect the profile on the assembly. A key variable was each oven’s unique heat transfer rate coeffi- cient, hence the need for an initial profile run on that specific oven. By capturing the essential cause and effect


data, it became possible to make a very accurate prediction model, based on the assumption that all PCBs in the relevant production run were identi- cal. That was a safe bet as the product BOM obviously had to be a constant, along with a very specific solder paste volume and placement of components. This prediction software was a big


help to engineers, especially in reducing NPI time and increasing equipment uti- lization. With the introduction of lead- free solder, the process window tight- ened up and made this task more chal- lenging. An average reflow oven is capa- ble of billions of alternative setups when changing each zone temperature and


Today’s smart reflow ovens can suggest optimal oven setups without running a single profile.


called the process window. Therefore, we can think of a reflow oven as a “profile making machine.”


Automatic Profiling’s Development Twenty years ago, it was common for a


process engineer to try different oven setups dur- ing new product introduction (NPI) until satisfied with the resulting profile on the assembly. Software was developed that allowed this “trial and error” method to be replicated on the PC. One


Whether we name it AI or machine optimization, the smart reflow oven


shows the potential of using massive amounts of data to create insight, to deliver actionable information, or


simply to communicate machine-to- machine for automatic decisions or adjustments within process criteria.


or more temperature zone set points were changed on the PC, perhaps along with a changed conveyor speed, and the software would immediately predict what the resulting profile would be on the PCB if the oven had stabilized on that new setup.


the conveyor speed in small increments over a wide range. This was the time when new, much faster prediction algo-


rithms, combined with sophisticated computers made a difference. Also, the prediction results were no longer only good or bad but instead offered a quality ranking of each resulting reflow profile.


Enter the PWI The introduction of the process window index


(PWI) was the final new invention that allowed for automated reflow oven optimization. The PWI quantifies the quality of each profile with a single number. PWI, which literally condenses hundreds of thousands of data points into a single number, is similar to the historic Richter scale. In the 1920s, there were very complex and competing methods to characterize the strength of an earthquake. Dr. Richter developed an efficient, powerful alterna- tive to chaos by condensing the information into a single number to quantify an earthquake’s force. A PWI number of 100 percent means that


100 percent of the process window is used, which is another way of saying that the reflow profile is exactly on the edge of the process window. A PWI of less than 100 percent means that the profile is in spec. The lower the number, the more the reflow profile is located toward the center of the process window. On the other hand, with a PWI greater than 100 percent, the profile is out of spec to larger or


Profile-making software churns through


billions of possible setups before selecting a “golden profile.”


because it results in a stable process that allows for more of the natural drift in the process during a production run without falling out of spec. Additional profiling optimization capabilities


became popular. Search criteria, such as selecting the oven recipe that maximizes the conveyor speed while keeping a deep in-spec profile became possi- ble. Or one could ask for the oven recipe using the least amount of electricity while still maintaining a certain minimum speed and PWI level. Or the engineer could request the fastest oven changeover by fixing the zone temperatures and only varying the speed. The equation had changed from “Tell me what happens if I do this?” to “This is the result I want to see. Make it happen, fast!”


Real or Fake AI? Whether we name it AI or machine optimiza-


tion, the smart reflow oven shows the potential of using massive amounts of data to create insight, to deliver actionable information, or simply to commu-


Continued on page 58


smaller degrees. One benefit of the PWI concept is the simplicity and speed with which a conclusion can be made. If you had ten process engineers in a room and presented each of them with the raw pro- file data — hundreds of thousands of data points — and asked their opinion about the quality of the reflow profile, you would likely get ten different answers. If you gave them the single PWI number, you would get the same answer from all of them, regardless of language or expertise. Perhaps the most significant benefit of the


PWI, however, was that now computers had a sin- gle number to rate the numerous profiles. With bil- lions of alternative oven setups, the prediction software would predict the resulting profile and its match to the process window billions of times over, each with its own PWI number. Computers then had an easy task of selecting an oven setup that resulted in a profile with the lowest PWI number. This could be done in just a few seconds. This


capability again allowed for greater optimization. The center of the process window is a good one


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92