Circuits Assembly - February 2008 - (Page 36)

Selective Soldering Breaking the Tape A high-mix, high-rel EMS finds selective tops masking and taping. 90% 40.00 any assemblers 84% of high-reli82% 80% 80% 35.00 78% ability circuits 74% 72% 72% 70% have turned to selective 30.00 67% 66% 65% 64% soldering as an alterna63% 60% 60% 58% tive to wave-soldering 25.00 56% 55% 51% selected underside areas 50% Original Process Time 20.00 or PTH components New Process Time 44% 42% 42% Time Reduction in % 40% using pallets. There are 15.00 a number of reasons, 30% but often it is because 10.00 20% wave soldering was not originally designed for 5.00 10% this. Defect levels can be high, and preparation 0% 0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 times – such as masking Assembly – become prohibitively Figure 1. Hand soldering versus selective soldering comparison at contract assembler APT long. Selective soldering Electronics. is a good way to avoid hiring a platoon of hand soldering technicians as orders (and throughput) “For example, I was hand-soldering four connecincrease. tors on a 0.090" board. With hand soldering, it would APT Electronics, a contract assembler of hightake 8 min. to hand-solder four connectors. Now I reliability military and avionics, faced this probcan do it in 4:37, start to finish. For a two-up array, lem. Initially, APT was processing high-rel prodto mask and wave solder 18 components took 25 ucts on pallets in a wave soldering machine, min. Now, we’re doing it with the selective machine complemented by hand soldering, but the comin 7 min. No masking, no pallets. We found that we plexity and high-mass nature of the products would need seven to 10 pallets at $300 to $500 per – thick boards with massive ground planes – pallet just to be efficient with the wave machine in made hand soldering difficult or impossible for a high-mix environment. That’s not to say that we many applications. Wave soldering was balky and don’t do any taping. If I have to use a little bit of time-consuming, and wasn’t delivering hole-fill Kapton tape in a few places to mask something, it’s requirements. Also, the large number of differwell worth it, because of what I’m saving overall in ent products – it’s a high-mix environment – had taping, touchup, masking and the rest. [But] prior to varying requirements and process recipes. this, we would mask the entire bottom of the PCB, in “Right now, I’m running 38 different prodpart because the customer did not want to spend up ucts through this machine,” says manufacturing to $3000 for pallets for 25 to 100 assemblies.” engineer Joe Garcia, “using only three ‘universal’ A preprogrammed selective soldering machine’s fixtures that cost perhaps $500 each. Prior to that, fountain can get solder into the holes despite the we used expensive custom fixtures for every part assembly’s high mass, but the process is more in a wave machine and still weren’t getting the automated (Figure 1). “Once you get it set up results we needed, especially in terms of hole fillproperly, programmed, dialed in, you just plug it ing.” A big problem was getting sufficient solder in and start running,” Garcia says. “It has cut our into holes for connector attachment on big backprocess time 50 to 70%, sometimes 80%. We’re not planes. masking or taping product comprehensively prior “A lot of time was eaten masking the entire to processing, and we don’t have the volume of assembly bottom with water-soluble or peelrework or touchup that we had, either.” able mask, or taping with Kapton tape, which is Rework has also been cut 30 to 40%, Garcia very expensive. We needed a unit that could be says, because the solder joints fill all the way to the programmed to selectively solder only what we top, even on heavy 0.120" backplanes with heavy wanted,” Garcia says. ground planes and gold antenna connectors. ■ M Ursula Marquez de Tino is a process and research engineer for Vitronics Soltec (vitronics.com); umarquez@ vitronics-soltec.com. 36 Circuits Assembly FEBRUARY 2008 % Reduction Time (min) circuitsassembly.com http://www.vitronics-soltec.com http://www.vitronics-soltec.com http://circuitsassembly.com

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Circuits Assembly - February 2008 Contents Caveat Lector Letters Industry News Market Watch Global Sourcing Better Manufacturing Maximizing Lean Copper As a Viable Solution for IC Packaging Embedded Active Components for High-Rel Products Cover Story: XRF Equipment As a RoHS Screening Tool Tech Tips Selective Soldering Test and Inspection Process Doctor Pb-Free Lessons Learned Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - February 2008

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