At RadiSys, no detail's too small.
Under the guidance of senior manager of supplier engineering Rob Rowland and director operations Thomas Huegel, manufacturing at RadiSys starts with a mindset that process control is absolute, and tweaks are antithetical to good process control.
Like many North American firms, RadiSys has shifted much of its volume production to EMS companies overseas. (To ensure adherence to company standards, RadiSys employs process and test engineers onsite at its primary contractor.) The factory now specializes in high-mix, low-volume (NPI) jobs, and changeovers take an average 15 minutes, thanks to a dynamic and sequential system. To that end, the company has invested heavily in feeders that, when we visited in mid-February, were set up three to four jobs deep, just paces away from the placement equipment. Even the wave machine has a second bath to shorten downtime.
To underscore the importance of repeatability, on each machine is a Mylar checklist that reminds of pre-run steps and critical parameters; they can be wiped clean between jobs.
Operators download machine programs, but no editing is allowed, Rowland says. "If you let people on the line edit, you get further and further away from an optimized process."
Similarly, process control charts are above each process, spelling out parameters, inspection frequency and trigger points. "These enforce the idea that we're serious," says Rowland. Some steps call for extra measures. For instance, a timer is set each time a jar of solder paste is opened, and cleaning commences once the time limit is hit.
Great emphasis is placed on machine calibration and maintenance. On the floor are DEK printers, Asymtek dispensing equipment, Universal placement machines, Heller 9-zone convection reflow, and a Technical Devices wave soldering machine. The primary final finish is immersion silver, with OSP the default second option. While its EMS supplier uses SAC305 for reflow and wave soldering, SnCu is used for wave in Hillsboro, although Rowland allows that a switch to Sn100 may be imminent.
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RadiSys places a "heavy emphasis" on the profiling strategy, says Rowland, using just six profiles for some 400-plus boards. Doing so facilitates process control and speed changeovers. Rowland likes a fast ramp: The first seven zones are the same temperature (235[degrees] to 245[degrees]C), with 240[degrees]C the target. The wave is set at 270[degrees]C for Pb-free.
The factory has been Pb-free for two years (Alpha solder) and has built thousands of mixed alloy boards. Interestingly, the shift to Pb-free has not led to changes in any land patterns or placement programs. That is not to say the transition was a no-brainer. Pad cratering defects have been observed on Pb-free boards, for example.
What we didn't see was an over-reliance on inline inspection. Instead, first-article inspection is performed offline, where solder volume and thickness measurements are taken. "We don't see the need for a lot of inline tools," explains Rowland, who has also worked for Benchmark Electronics. "You tend to lose focus on the process with a lot of inline tools." Test and inspection is performed using a Landrex AOI, a Test Research TR-8001, HP 3070 ICT, and Teradyne flying probes. All boards are designed for ICT.
The proof is in the performance: DPMOs are less than 40, Rowland says.
Mike Buetow, Editor-in-Chief
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|Title Annotation:||Caveat Lector|
|Comment:||At RadiSys, no detail's too small.(Caveat Lector)|
|Date:||Apr 1, 2007|
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