Dual-lane reflow ovens have been available for years, permitting two boards to be run at the same time in parallel. Until recently, circuit board manufacturers have been limited to processing the same boards or boards with like mass in each of the lanes, but dual-lane reflow ovens with independent lane speeds now make it possible to run boards with larger differences.
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http://www.thermador.com/blog/q = the thermal energy being transferred to the board[FIGURE 9 OMITTED]Press Room:
http://www.thermador.com/about/press-room/whereWe then followed the procedure used with the eutectic profile and varied the belt speed [ or -]15 IPM from the starting point. The new peak temperature, TAL and soak time were recorded for the various belt speeds with each of the three test boards. The results are shown in FIGURES 8, 9 and 10.Thermador is part of BSH Home Appliances Corporation, a fully-owned subsidiary of Bosch and Siemens Home Appliance Group, the third largest appliance manufacturer in the world. For more information, visit
www.thermador.com or follow us on Facebook and Twitter at
www.facebook.com/thermador and @ThermadorHome , respectively. For Thermador customer service, call 1-800-735-4328.In August 2009, a report published by BTU (1) showed how changing the belt speed, zone set points and convection rate affected a solder reflow profile. It looked at how the furnace settings affected the peak temperature, time above liquidus and uniformity of two SMT boards. This new study varied the belt speed from 30 IPM to 60 IPM on a 75 gm, 360 g and 520 g board with eutectic and Pb-free recipes on a Pyramax 150 12-zone nitrogen reflow oven. The change in peak temperature, time above liquidus and soak time of each combination was recorded.Next we wondered if predictive software such as KIC Navigator could be used to forecast the profile. We had used a KIC Explorer to obtain the original profiles for the trial, so it was an easy step to see what the KIC Navigator would predict if told to change just the belt speed on the Pb-free baseline runs for each board. The software predicted peak temperatures that were within 2[degrees] to 3[degrees]C of what was actually measured. The peak temperature predicted results vs. actual for the three boards, shown in FIGURE 11.By introducing a heavier or lighter board to the equation, the a and A factors change. Thermal energy absorbed by the board (q) then adjusts so the equation remains balanced. This change in thermal energy (q) results in a different board temperature. To maintain the board temperature, we must change either the zone set points ([DELTA]T) or belt speed (t).[DELTA]T = the temperature difference between the gas (convection) and the boardWhen we move the board parameters to one side of the equation and the oven parameters to the other side, we getMedia Contacts Chris Yemma/Sung Choi DGWB PR (714) 881-2412/881-2345 office (619) 850-7240/(949) 422-7156 mobile
cyemma@dgwb.com schoi@dgwb.com[FIGURE 4 OMITTED]q = a * t * A * [DELTA]T Eq. 1[FIGURE 5 OMITTED]Next the belt speed was changed in steps of approximately 5 IPM to a maximum and minimum of 15 IPM from the starting point on the three boards. We recorded the new peak temperature, TAL and soak time for each step. The results are shown in FIGURES 3-5.t = time the board is in the heatEutectic recipe. The first step in the trial was to establish a baseline recipe that produced a standard ramp-soak-spike profile with the 360 g board at 45 IPM (FIGURE 2). The peak temperature was targeted at 220[degrees]C, time above liquidus (TAL) at 60 sec, and the time between 140[degrees] and 170[degrees]C at 70 sec.A = the surface area the heat sees[FIGURE 6 OMITTED]If we could accept the new TAL and soak times, the new second board belt speed would work. If we could not accept the new TAL or soak, we would need to accept a different peak temperature on the new board or try different set points on both boards.Practical application. We then applied the data to the real-life situation of running two different boards in the same oven. We started with the 360 g board in one lane and wanted to run the 75 g board in the other. Figure 3 revealed we needed to increase the belt speed to 58 IPM (see FIGURE 6) to maintain the same peak temperature on both boards. Meanwhile, Figures 4 and 5 told us that the TAL and soak of the 75 g board would shorten to approximately 45 and 55 sec. with the 58 IPM belt speed.[q/[a * A]] = t * [DELTA]T Eq. 2[FIGURE 8 OMITTED]When the belt speed was varied, all three parameters changed as in the eutectic profile. The TAL changed by 80 sec; the soak time changed by 20 sec., and the peak temperature changed by around 15[degrees]C.The board weights had the same effect on the peak temperature that we had with the eutectic solder profile. At the lower belt speeds, the difference between boards was about 7[degrees]C, and at the faster speeds, it was close to 13[degrees]C. But unlike the eutectic profile, where the mass did not affect the TAL or soak time, the TAL was about 20 sec. longer with the lighter 75 g board. (This most likely was due to the ramp to peak profile shape.)Visit Two Peas and Their Pod:
www.twopeasandtheirpod.comNow we have the ability to run different speeds in each lane; it is the process engineer's responsibility to develop the recipe that will satisfy both boards. The following gives practical insight into a method to obtain this recipe.The belt speed change affected all three parameters. The TAL and soak time were changed by almost 50 sec, and the peak temperatures varied by around 15[degrees]C.[FIGURE 2 OMITTED][FIGURE 3 OMITTED]Thermador's food-blogger partnerships are one of the key marketing initiatives of the luxury-appliance brand's overall revitalization campaign. Targeting the culinary enthusiast, or those most passionate about cooking and entertaining at home, the Thermador 2011 marketing campaign also focuses on two steam-focused product debuts: the Steam &
Convection Oven, which was unveiled in October 2010, and another industry innovation set to launch this summer.To begin, understand factors that affect the transfer of thermal energy from the heater in a convection oven to the board. In most cases reflow oven fans push gas (air or nitrogen) across a heated electric coil to increase its temperature. Then the hot gas is distributed to the product through a series of holes in an orifice plate, as shown below. The equation that describes the transfer of energy from the hot gas to the board is well known[FIGURE 1 OMITTED]As expected, the board weights had an influence on the peak temperature with the heavier board being 7[degrees] to 10[degrees]C colder than the light board. But there was little difference in TAL or soak time between the boards.[FIGURE 7 OMITTED]
Next we wondered if predictive software such as KIC Navigator could be used to forecast the profile. We had used a KIC Explorer to obtain the original profiles for the trial, so it was an easy step to see what the KIC Navigator would predict if told to change just the belt speed on the Pb-free baseline runs for each board. The software predicted peak temperatures that were within 2[degrees] to 3[degrees]C of what was actually measured. The peak temperature predicted results vs. actual for the three boards, shown in FIGURE 11.
Author: Fred Dimock
