Survey Aids Selective Soldering Process Selection
Published: 30 May 2007
by Staff
ATLANTA – Manufacturers perplexed about which type of selective soldering process to use might find helpful the results of a recent survey by Stone Mountain Tool.
The survey responses revealed valuable information about different types of selective soldering machines; criteria to consider when choosing the right machine to fit a company’s goals, including advantages and disadvantages of each; cycle times, startup costs and more.
President David Duke presented the results of the 40-question survey of about 30 customers at an SMTA Atlanta chapter meeting last week.
In the talk, Duke discussed single-point nozzle, point-to-point single nozzle, mini wave, multi-orifice nozzles, and selective soldering pallets. To choose the most appropriate type, Duke suggested the following criteria based on his survey results: the volume and consistency of boards to run; the layout of solder-side components (spacing and location of PTH leads to mounted SMDs); the height of SMDs mounted to the solder side, and the number and location of PTH leads to be soldered.
Cycle times were another point of concern. He said selective machines with point-to-point single nozzles spend 2 to 4 seconds per PTH lead, and that the cycle includes travel time from lead to lead; for mini wave nozzles, it is 10 to 15 seconds per lead set and the travel time from set to set; for multi-orifice nozzles, cycle time is 30 to 60 seconds, and for selective pallets 15 to 30 seconds plus pallet load and unload. Most machines are automatic, but can be manually loaded and unloaded if necessary, Duke said.
Assuming the equipment is present, startup costs for point-to-point and mini wave include program time and changeover, which takes 15 to 30 minutes. Multi-orifice nozzles cost $1,000 to $15,000 based on size and complexity, and changeover for multi-orifice is one to three hours. Pallets run in the range of $2,000 to $6,000 typically, he said, with a changeover time of 15 to 30 minutes to reset machine profiles. (This requires about 10 pallets, typically about $300 each, he added.)
Duke emphasized that process quality boils down to board design, especially with regard to spacing. Other items his customers noted that were particularly important for quality are nozzle and pallet designs; program integrity; flux applicators; pre-heat consistency; lead length (nozzles require longer leads, while pallets require shorter ones); the height reach of the nozzle or pallet aperture walls, and nitrogen, which helps for a good, clean environment, he said. But flux, he stressed, is most important.
With regard to Pb-Free and soldering, Duke explained, “The smaller the pot, the less expensive to process.” He also said there were no significant process adjustments from a soldering perspective for Pb-free. And again, the importance of flux was stressed. The only major drawbacks he mentioned with Pb-free are a slower process and a limited history with which to base processes on.
Duke shared the disadvantages of each soldering type: Point-to-point and mini wave both have a slower process on high pin count; inconsistent pre-heat; flux applicator variations; the highest rework percentage, and difficulties with program integrity and tuning.
Drawbacks for multi-orifice nozzles include the cost of complex nozzles, changeover time, and difficulties with startup and process tuning. Also, preheat paces the cycle and cycle time is ultimately difficult to predict.
With pallets, there are significant costs for purchase and storage. Startup and process tuning are difficult, and the pallets have limited use: generally a cycle life of 8,000 to 10,000, he said.
On the positive side, point-to-point, mini wave and multi-orifice nozzles are able to clear tall solder-side components. Point-to-point and mini wave are also flexible and have minimum startup costs. Multi-orifice nozzles have faster cycles on complex boards and better yields.
In the end, pallets are the most versatile, according to Duke’s survey results. They also have the fastest cycles and have additional features not seen with other options, including a mechanical component, masking horizontal alignment, etc. Pallets also have the best yields once the process is tuned.
