SMT Trends & Technologies: It Pays to be Frugal
October 16, 2012 |Estimated reading time: 5 minutes
Electricity consumption by manufacturing equipment is rarely seen as a major manufacturing cost. Materials and components, manufacturing equipment, and the salaries of production personnel are traditionally thought of as the main cost concerns for a company. But is this true? The price of energy and raw materials is quickly rising due to the growing scarcity of fossil fuels and materials combined with a growing demand from upcoming economies, particularly BRIC countries. Recent news from both India and China imparts that their economies are developing so fast that the electricity supply from power plants is insufficient to fulfill energy needs (Figure 1). This unbalance results in frequent power cuts. Figure 1: Power shortages will occur frequently in strong growing economies. Low-energy electronics manufacturing equipment helps maintain production--more production for the same energy--and also saves money. A recent comparison suggests that an average high-volume assembly plant could save nearly half a million dollars a year on energy related costs alone, and that figure can only rise.
First, the Reflow Oven
A typical SMT flow line consists of a stencil printer, PCB handling equipment, pick-and-place machines, a reflow oven, and test and repair equipment. The reflow oven will use the most energy, followed by the pick-and-place machines and test and repair stations.
A few options can reduce the energy consumption of the reflow oven. First is optimizing the oven temperature profile. Reducing the oven belt speed by 10 to 12%, combined with reducing the peak oven temperature to approximately 235 to 245°C, will reduce the reflow oven energy consumption by some 10 to 15%. Typical hourly energy consumption per reflow oven is 8 to 12 kWh. Of course you should verify on forehand if this belt speed reduction is acceptable in relation with the production needed. For instance: If 200 boards per hour are needed and the board length is 250 mm, this means that your belt speed should be higher than 0.833 m/min. Overall consumption is mainly determined by the number of heating zones in the oven and, hence, the oven length. The longest reflow ovens in a flow line consume approximately 50 kW (10 heating zones).
Second, Pick-and-Place Machines
To compare the energy consumption involved for pick-and-place, you first need a model showing the different energy consumption categories. Four categories can be distinguished: Driving (electric) motors and machine controls; generating vacuum and/or compressed air; lighting and heating/cooling of the machine environment; and reworking defects caused by pick and place.
A comparative study performed by Assembléon has shown large differences in energy consumption related to the real output of different pick-and-place machines. These differences come from the different machine types. Two main types exist: Sequential pick and place, where all pick-and-place actions are performed sequentially, using multiple pipette placement heads, and parallel pick-and-place, where pick-and-place actions are performed in parallel, using single or only a few pipette placement heads on multiple, parallel operating, placement robots. Figure 2: Sequential placement versus parallel placement: Fast and heavy versus slow and light.
Sequential pick-and-place machines have considerable accelerations/decelerations on (relatively) heavy placement heads and these need more energy (remember that the equation for kinetic energy is ½ mv2). Parallel pick-and-place machines have much lower accelerations/decelerations, acting on much lighter placement heads requiring much less energy.
Multiple pipette placement heads, found in sequential pick-and-place machines, also have greater vacuum consumption since all available pipette positions need to be ‘energized’ with the vacuum to hold all components in place. Vacuum consumption in a parallel pick-and-place machine, with considerably fewer pipette positions, will be much lower. Equipment on a flow line takes up area, also for the operator, which also takes energy to illuminate and (air) condition.
Equipment with a small footprint per unit output will minimize energy consumption. Small machines can also allow the use of smaller buildings with lower building costs…small is beautiful.
Third, Rework and Repair Stations Finally, the defects per million placements of a pick-and-place machine will have considerable influence on the rework rate and, hence, the number of rework stations needed. Compare a sequential machine with a typical DPM rate of 30 with a parallel machine with a typical DPM rate of 10. Assuming that a typical board contains 1,500 components, a DPM figure of 30 means that one board out of 22 will be defective. The literature shows that approximately nine minutes are needed per rework action, including finding the defect, de-soldering, component and solder preparation, component placement, component soldering, and inspection. Flow lines with a 20-second cycle time will, on average, generate a rework action (taking an average of 540 seconds) every 444 seconds. This requires two rework stations!
If we compare this to parallel pick-and-place (DPM rate of 10), one board out of 66 will be defective, so generating a rework action every 1,333 seconds (again, average rework time 540 seconds). Only one rework station is needed. This not only saves space in the line, but also investment and energy costs (an average 2.5 kW per rework station).
Energy Savings of $420,000
Results from the study comparing different pick-and-place machines on the market show big differences in energy consumption. Six models were compared (A to F). The most efficient model, a parallel machine, had an average annual energy consumption of 100,000 kWh (per 750M components placed) against 380,000 kWh (same number of components placed) for the least efficient model. This is a difference of 280,000 kWh per year for pick-and-place alone. Add the potential savings from reflow soldering (estimated at 15%) and you end with total savings of approximately 300,000 kWh per year. Figure 3: Comparing energy consumption of six different pick-and-place machines (output: 100 kcph).
With the average U.S. industry energy price of $ 0.065 per kWh, this means saving $19,500 per year per line of 100,000 cph production capacity. Considering an average high-volume electronics manufacturing plant has approximately 12 lines (average 30-second line cycle time), potential annual energy savings per plant [ITALICS] are more than $420,000.
It pays to be frugal! In addition to playing the clarinet in two bands, Assembléon’s Sjef van Gastel has another passion: SMT. He has been with the company since its start-up as a Philips division in 1979. As the current Manager for Advanced Development, he combines his experience as systems architect and machine designer to explore technical and business opportunities from emerging technologies. van Gastel holds many patents and is a frequent speaker at international conferences related to SMT. He is also the author of “Fundamentals of SMD Assembly,” which has become a standard piece of literature in the industry.