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September, 2016
What Makes a Reflow Oven “Smart?” By Bjorn Dahle, President, KIC Thermal T
he ultimate objective for an electronic manufacturer is to manufacture the required qual-
ity product in a sustainable way, to deliver the product to the customer within the allotted timeframe, and to do so at a cost that allows the manu- facturer to be profitable and the price to be competitive. Investing in intelligent mach -
ines for their own sake is a waste of money. However, such investments are important to achieving the ulti- mate objective, particularly as we enter a new manufacturing era. There is much talk these days about the need for factories to transform themselves into smart factories full of intelligent machines interconnect- ed by the Internet of Things (IoT). While easy to understand on a con- ceptual basis, what does it mean in practical terms? What makes a machine “intelligent?” Is there a met- ric that can be used to evaluate the “smartness” of a factory? Perhaps more importantly, why should we care?
This new manufacturing era is
being characterized by: l
l
Mass customization resulting in frequent production changeover.
l Heightened competition. l
l
Falling prices of manufactured goods.
The need for sustainable manufacturing.
Customer demands — zero defects, full transparency and traceability.
It is not necessary to burn down
the old factory to build a new one. Most existing machines and infra- structure can be upgraded easily with smart technology. There is a growing understanding in the elec- tronics assembly industry that intel- ligent or smart machines have bene- fits in a number of areas. Here the reflow oven is used as an example for illustrative purposes, as that is KIC’s area of expertise, but the principles are relevant for most, if not all, machines.
Process Transparency The reflow oven is often thought
of as a black box, because we cannot easily see what happens to the unsuspecting PCB after it disappears inside the roaring oven tunnel, and is
blasted with hot air for seven or eight minutes. Peter Drucker, the famous
Austrian-born business thinker, believed that to manage a process well, it must be fully measurable. A half-step toward making the reflow process transparent is to make
continuous and real-time measure- ments, as if a video camera were to be embedded in the oven and run non- stop. It is not enough to do good work some of the time, or even most of the time. Production has to be right all of the time, and data is required to enable it.
more for an oven to stabilize on a new temperature setting, especially if the new recipe is cooler than what had been previously used. A smart oven, however, is
equipped with software to search for a “golden recipe” that can process all the various assemblies in spec with- out any recipe change. This smart software can literally scan billions of oven recipes and predict the result- ing PCB profile for each. It then iden- tifies a common recipe that can process all the PCBs in spec. Whether such a golden recipe exists depends on the capability of the oven, the spread in thermal mass between the assemblies, and the variation in individual PCB process windows. In many cases, the reflow oven
Smart oven technology is a combination of automated data gathering and real-time access to that information.
machines collect more information. For the oven itself, this means creat- ing a machine with continuous moni- toring that provides data on the selected oven recipe, zone tempera- tures, conveyor speed, time-stamped board in/board out, and board jam detection. While such data is useful, it is insufficient. A smart oven also needs process transparency. A reflow oven’s main purpose is
to create strong solder joints while adhering to the tolerances set by the related solder paste, component and substrate vendors. To ensure that the oven produces each assembly in spec, the PCB thermal profile is measured. For process transparency, the profile and its relationship to the relevant process window must be measured continuously in real-time. When profiling an oven on a periodic basis, production is running blindly and process transparency simply does not exist. Periodic snapshots of the process
(as in a manual profile) are similar to taking a still picture with a camera. There is no dynamic information about the process, nor is there any vis- ibility into the process between snap- shots. Process transparency requires
The process can be linked easily
to the individual assembly by scan- ning each PCB barcode. We then have information about what each PCB experienced during the thermal process. Such information has great value for traceability and trou- bleshooting. With instant yield trou- bleshooting, more production uptime results in significant cost savings.
Flexibility Market trends in the vast
majority of industry segments indi- cate a strong movement toward the mass customization of products. This means shorter production runs and more frequent line changeovers. This
is not capable of such a golden recipe. In that case, the software searches for new recipes by holding the zone temperatures constant and only varying the conveyor speed. While the oven may need 30 or more min- utes to stabilize on new temperature settings, the conveyor speed resets immediately. In the worst case, the oven is
not capable of processing all the assemblies using the same zone tem- peratures. The software then identi- fies two or more recipes that can handle a wide range of assemblies using a method called grouping. You may think of this as a more accurate method of what happens in SMT fac- tories every day where an engineer judges a new incoming PCB assem- bly to be processed using recipe A, B or C. There will be some downtime associated with oven changeover, but it is limited to the few groups that are set up as opposed to every new PCB.
It is not necessary to burn down the old factory to build a new one. Most existing machines and infrastructure can be upgraded easily with smart technology.
is a challenge for many automatic machines as they do a better job of cranking out identical products rather than switching between dif- ferent tasks. The reflow oven is often the bottleneck in the SMT line regarding product
changeover because it can take 30 minutes or For quicker NPI, ovens with
intelligent databases suggest the appropriate recipe without running a profile. The database uses collected information about the relationship between the oven thermal properties, PCB thermal mass, PCB process
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