Selective soldering machines are a good way to "finish automation", if the design of the PCB is conducive to the application with just a few components to solder.
Your points are good. A decision matrix for selecting a machine might also include: * Maintenance costs (ie, periodic maintenance requirements, replacement parts cost, etc) * Fixture costs (ie, chimneys, pallets, etc) * Repeatability of the process * Set-up and change over time * Flux application and control, because over- and excess-spray can be very detrimental to cleanliness and obtaining hole fill is important. * Solder level (ie, measurement, indication, etc) * Nitrogen consumption and ppm levels, if running no-clean flux * PCB recognition (ie, fiducial, hard-stop, etc) * Preheating profile adjustment and control (ie, ramp rate, peak temperature, dwell, etc) * Warped PCB damage avoidance. * Ease of programming. Properly, with offline programming that is generated from CIM software [eg, CIMBridge, CircuitCAM, etc] to avoid teaching from Gerbers or entry by hand.
Other points are: * Also, be wary of the promise of very tight spacing capabilities. For instance, a supplier might rightly claim the ability to solder through-hole leads within 0.020" of a nearby SMT component. While accurate, this may be possible only with a 0.150" clearance on the other side of the through-hole lead and maybe use the lead to wick the solder to the hole. Er, cute stuff like thet. * Some machines require peculiar fixturing for each PCB design that further increases the cost of the machine. * Selective soldering machines are very limiting, but are a good option for a very specific application or PCB design. * Consider evaluating chimney versus programmable / conveyored machines separately. * Consider evaluating selective soldering machines versus pallets for the same application. Typically if the PCB has 10-15 components (which is a lot) and the release quantity is GT 100, the cost justification for a selective soldering machine might be very difficult.
Finally, we have discussed these machines on SMTnet in the past, for instance http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=4586Message17907& Search the fine SMTnet Archives for additional background.
reply »