With the spotlight on lead-free solder, oven capabilities are coming under tight scrutiny. But, just where does this really fit into the full reflow picture? Are there equally important issues pushing oven developments? As new capabilities are unveiled, what is being done to help existing customers optimize older ovens? To clarify these issues, seven major oven manufacturers agreed to share their opinions, strategies and latest equipment developments with EP&P.

The issue of lead-free is not so much the higher liquidous (standard eutectic 183°C; lead-free 217-221°C). Most ovens easily can handle the temperature. For those that may feel more confident with an added thermal "boost," high-temperature upgrades are available. But, higher temperature is not the point. The profile process windows are shrinking by as much as 30° because, as Marc Apell, product manager at Speedline-Electrovert, explains, "You can't ramp up to the maximum peak temperature of the solder range because it surpasses the limit for both component and board material tolerance thresholds. Therefore, it becomes more of a flat profile — held at the low end of liquidus over a longer period of time." (Fig. 1).

"This puts a significant emphasis on smaller product temperature differentials, increased oven performance and overall process repeatability to ensure quality output," adds Al Cabral, marketing, BTU International.

Oven manufacturers began working on this issue as soon as it arose, even though full implementation may be well in the future — and, may never pose the challenge it appears to be today. As they noted, lead-free is only in beginning stages, and there will surely be changes and improvements. Component, PCB material and paste manufacturers are all working on the issue. Because all parties have a common goal of easing product processing, it can be assumed that whatever advances materialize will benefit the reflow process. Moreover, today's significant challenges may not even exist in the future.

However, improvements driven by this issue will enhance overall oven capabilities in the long run. Improved designs and control software are in development. One key element comes from outside the inner circle of oven manufacturing-partner arrangements with profile OEMs.

Only a few years ago, profiling equipment was basically in use only at the larger OEM manufacturing facilities. Since profiling software and oven control software "spoke different languages," profiling programs ran on independent computers. Advances in software development, plus the looming specter of shrinking process windows, brought the two industry segments together to create "self-profiling" ovens. This partnering arrangement fans out across the whole customer base, so all ovens — old or new — have support from both the oven manufacturer and its selected profile provider(s).

If there is any single issue that oven manufacturers both agree and disagree on with equal vigor, it would be the area of profiling providers. All believe in the benefits, but, there are widely differing opinions regarding who and how many profile partners offer the best solution.

Fig. 1: Compared to a standard eutectic profile which hits peak quickly and cools down quickly, lead-free holds at low liquidus longer, creating a flatter profile.

BTU has established working relationships with KIC, ECD, DataPaq and CMD. "We like to think that BTU helped pioneer the interface between profiling and oven control software," says Cabral. "A few years ago, BTU approached KIC and presented the idea of linking the oven to the profiler. In concert, we created compatible software interface modules that successfully communicate. This provides a 'self-profiling' reflow oven. Our first experience with KIC was successful and, soon thereafter, we partnered with ECD to a similar degree of success. We have since provided this same interface to a number of other partners."

Like SEHO, Rehm, USA has an arrangement with ECD only. "Our systems are all equipped with ECD profile generating software as a standard feature," says Sabine Berger-Eckle, marketing. "We compared the products available and decided that ECD provides the best solution to easily allow our ovens to adjust themselves for optimum reflow."

Vitronics-Soltec claims to be one of the first companies to see the benefit of integrating profiling and oven control software. "We have an open interface that we have discussed with all of the major profiling companies," says Eddy Nijhof, product manager. "We currently have installed ECD and KIC profiling suites onto our ovens." He explains that the reason for selecting these initial providers is because both profiling packages work from a known database of solder pastes. This is the normal starting point that all engineers use when establishing product profiles. "They do take a different approach on how to present their data; KIC uses a lot of multimedia while ECD is geared more toward the engineer. Ultimately, either is an excellent added feature to our ovens."

Fig. 3: SEHO’s flux elimination system condenses and collects all residues in a bottle for clean disposal.

Nitrogen is an issue tied to lead-free because of the higher processing temperatures. Higher temperatures will break down the organic solderability coating (OSP) on boards, causing pad oxidation. A nitrogen processing atmosphere minimizes solderability issues like this, and improves solder joint aesthetics. But the cost of nitrogen varies radically by nation and by how it is generated.

"Manufacturers also need to focus on establishing a reliable and controllable low ÄT across the heater panels to ensure consistent processing of the large dimension boards (27 in.- 30 in.) seen in telecommunications and networking today, " says Peter Whelan, Conceptronic. Sabine Berger-Eckle, Rehm USA notes that this type of control is equally important when processing small, highly sensitive components. In both cases, this is true regardless of the solder formula used. Marc Peo, Heller, adds that flux elimination, reducing the cost of ownership including electrical and nitrogen consumption, and downtime associated with maintenance are equally important industry drivers.

Figs. 5a and 5b: Multi-port blower system (left) and flux management air flow system (right) in Profile series ovens.

In developing solutions, all oven manufacturers have both new and existing customers' needs in mind. Most new features are available in retrofit versions for older ovens.

BTU is taking its furnace technologies for specific industries and crossing the benefits over to all oven users. Closed loop convection control (Fig. 2), was developed by BTU for packaging applications in the semiconductor industry. This feature is available as an option that allows all users to dial-in convection rates with precision while under recipe control.

SEHO is focused on a comprehensive package of features including lead-free capability of the complete system (high-temperature resistance), minimum emission of heat (less than 2 kW), minimum consumption of nitrogen and minimum consumption of energy (only approx. 10 kW/h with the largest system). The company also has a new emissions elimination system (Fig. 3). "This new technology collects concentrated residues in a bottle for easy disposal," says Heike Schlessmann. "More than 90 percent of all residues are collected in this way with no contamination of water for cleaning."

Vitronics is concentrating on control. Their precision profiling series brings the coolers into the reflow recipe, providing total control over the entire oven length from heat up to cool down. Gas temperature is controlled in a narrow window using PID control and control thermocouples located close to the product.

Their new flux flow control (Fig. 4) takes all contamination out of the tunnel, and feeds it to the available exhaust stack filter through insulated tubing. Condensation takes place in the exhaust stack filter condensing area. Residue then moves through very inexpensive ($2-$3) filters.

Conceptronic has actively approached solving the temperature stability challenge facing large boards and small components. Its new Profile series of ovens incorporate dual port blower systems (Fig. 5a), which puts more air velocity at board level. This makes uniformity across the heater panel much greater, and enables stable processing of 27-30 in. boards easily with a low ÄT across the heater panel. As for flux management, the unique air circulation within its oven is optimized to keep flux from accumulating in the first place (Fig. 5b). "We bias the air from the center of the oven to each of the ends, forcing it in that direction. The only flux buildup is in the cooling section, which is very easy to clean," says Peter Whelan.

In the area of flux management, Speedline-Electrovert has developed the process volatile active cooling (PVAC) system. PVAC, combined with its auto-clean software creates a system that collects all flux volatiles into a small container that can either be dumped and reused or thrown away, greatly reducing maintenance issues.

Fig. 6: The V8 series from Rehm, USA offers improved heat transfer, reduced power consumption and a modified cooling zone.

Rehm USA has implemented improvements in overall flexibility and reduced power consumption (Fig. 6). "Our existing SMS-V6 reflow soldering system demonstrates excellent heat transfer characteristics, and can be operated with air, or a nitrogen atmosphere. We offer a flexible conveyor system with a great deal of freedom, including double- and single-lane conveyors with various types of center supports," reports Sabine Berger-Eckle.

There is not enough space to go into detail, but the following should be enough to whet engineering appetites.

SEHO is planning to integrate a pyrometer at the peak zone to directly measure the temperature of a few PCBs of the same product, and calculate a product-specific tolerance. Each product processed is documented and checked to ensure that the measured temperature is within a predetermined tolerance. If not, an alarm would be initiated.

Vitronics-Soltec is planning a more "intelligent" oven, using operator interfaces (PCs) with standard network ports as a start.

BTU International wouldn't get specific about its new technology, but indicated that its expansion of the Pyramax platform will "raise the bar" in terms of reflow performance.

Conceptronic is working on a control system in their software that will be able to deliver any type of SPC data and analysis on the fly to wherever it is needed.

Speedline-Electrovert is designing a "no-clean machine" that can monitor and maintain itself, give warnings, updates, and basically "tell" the operator which tasks have been completed, and which need to be scheduled.

Heller recently patented a new heater module technology that drives down the ÄT on the boards to virtually provide equilibrium heating regardless of board size, shape or type of components. All 0201 components (capacitors and resistors about the size of a pinhead) are one focus for this technology. Because this module utilizes an extremely efficient delivery system, it also reduces nitrogen and electrical consumption.

Rehm, USA has reduced overall dimensions with its new "V8" oven. It has incorporated a wealth of features including a new tool called the capability controlled system (CCS) — an integrated hardware/software tool for online monitoring of the oven's machine capability. Machine capability coefficients can be calculated online for each of the zones, as well as for the conveyor system. They also are looking into condensation soldering, a totally new oven technology. One possibility is incorporating the condensation principle into a new generation of ovens.

The oven manufacturers have a good handle on controlling the variables associated with lead-free, and partnering with profile OEMs is a major part of this. There are some interesting new developments on the horizon. It appears goals are set to enhance the capabilities of the next generation of ovens, making life easier for operators and more profitable for owners. It will be interesting to see how some of these future concepts materialize.