Pentaplex, Inc. (Elgin, IL, www.pentaplexinc.com), a small, privately owned printed circuit board (PCB) fabricator, recently reported that it has finished pilot testing a lead-free hot air leveling (HAL) process that meets its customers' requirements with a minimum of disruption to its manufacturing processes. The company claims to be the first PCB facility to use this process in the U.S.

This lead-free HAL process is a result of the collaboration between Pentaplex and Florida Cirtech, (Greeley, CO, www.floridacirtech.com), a manufacturer and supplier of proprietary chemistries to both the electronics assembly and PCB fabrication industries. Because of the technical background of Chuck Lawrence—the founder and chief process engineer of Pentaplex, the experience of the company's employees, and the unique features of one of its two hot air levelers, Glenn Sikorcin, a Florida Cirtech representative, felt that Pentaplex would be ideal for a pilot operation of Cirtech's SN100CL process.

This product is a form of eutectic tin-copper that was developed and patented by Nihon Superior as a wave solder replacement. It involves the addition of trace nickel to the alloy, which seems to have eliminated many of the problems associated with the tin-copper alloy. SN100CL is a version of this alloy that was created for hot air leveling applications.

The major challenge in hot air leveling with lead-free solders is the heat lost at the board surface-solder interface. The temperature of the molten solder has to be maintained there during application for results to be acceptable, which means a rapid molten metal turnover and strong heat transfer capability. Pentaplex's older Quicksilver model HAL machine had both of these design features.

To convert the hot air leveler for lead-free solder, the 63-37 eutectic solder was drained from the bath, the stainless steel tank surfaces were scoured clean and reoxidized, the air supply was upgraded and the temperature controller's sensitivity was improved. Then the HAL machines' operating parameters were fine-tuned, with bath temperature and dwell time the biggest concerns. Once those had been optimized, the testing of various panel types for compliance to standards began.

The results were excellent. Several types of PCBs were tested: high-density; fine-line; multilayers up to 24 layers; vias; large panels; small panels; thick and thin panels; and copper thicknesses up to 10 oz. copper. According to the companies, all of these types passed through the lead-free hot air solder process with results comparable to normal solder. Both tin-copper and tin-lead-coated component leads were tested in soldering studies, with joint strength and metallurgical structures proving satisfactory. Similar tests run with panels exposed to simulated one-year storage conditions had similar results with good wetting and joint strength.

When the tests were completed, the companies determined that using SN100CL in the Quicksilver hot air leveler produced a solderable surface that was smooth, bright and relatively flat and easily cleared from through holes while leaving a sufficient thickness of solder for component solderability. The lead-free coating seems to maintain these characteristics for up to one year under the same conditions as tin-lead solder.

The critical factor in successfully adapting the SN100CL system was having a hot air leveler that can replace lost heat fast enough to keep the solder temperature steady. All other preparatory and fluxing operations were the same as for the prior tin-lead HAL operations, keeping the cost of installation fairly low.