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Selective Soldering:
Cost-effective Replacement for Production Hand Soldering
December 31, 1969 |
Estimated reading time: 6 minutes
By Alan Cable, A.C.E. Production Technologies
Selective soldering early on became established as an automated, robust method of soldering individual components that could not be hand soldered, and a way to automate individual component soldering processes that could not be wave soldered properly in pallets (the cost of custom pallets was a significant factor as well) or assembled with solder fountains. Selective soldering adds consistency of results, repeatability, and speed to the soldering process and has become an integral part of most PCB assembly lines.
However, selective soldering has moved beyond the role of being a problem application solution and into the soldering production mainstream. Flexible innovations, better user interfaces, and simplified programming have now made selective soldering a replacement for most production hand soldering. Not only is selective soldering as a process more reliable, consistent, and faster than hand soldering, but selective soldering systems now have a relatively fast ROI and compare favorably to the labor costs of using multiple hand-soldering technicians for any given job. Selective soldering can be used for a much wider range of soldering tasks traditionally performed by hand soldering. Thus, in many instances, a single selective soldering machine run by one or two operators can replace five or more hand soldering technicians and double or triple the throughput as well as increase yields per given shift, for faster machine investment ROI and long-term yield and profitability advantages.
The TechnologyThe primary benefits of selective soldering, when the process technology first emerged some years ago, were the ability to solder selected areas, or devices mounted on a PCB, more efficiently and with better results than wave soldering the assemblies in expensive custom pallets. As the technology developed, it became more widely applied as an alternative to other types of soldering, including production hand soldering. It's fairly well known that automated selective soldering is more consistent by nature than hand soldering, and faster. However, there are still plenty of manufacturers reluctant to replace skilled hand solderers with a machine simply because the cost-difference numbers are not available, or they are concerned with long-term equipment investment ROI in these tight economic times. After all, one might ask, how soon would an investment of more than $50,000 sometimes as high as $100,000$200,000 for a higher-end machine with more robotics pay for itself? Would there be enough volume to justify it?
There are good, solid cost comparison numbers available, and the respective differences between hand soldering and selective soldering are so disparate as to make a compelling case for investment in selective soldering technology. Also, one need not be concerned about losing valuable, skilled employees who are long-time assets to the company. A selective soldering machine requires from one to two operators, and solderers whose jobs are replaced by the machine usually are assigned to other tasks or needed in other areas.
Case Study: Increased ProductivityOne representative example is the installation of a selective soldering machine at Onset Computer Corporation of Bourne, Mass. Onset has a low-volume, high mix manufacturing environment. Onset's management set a company-wide goal of double-digit growth for 2007. For manufacturing to achieve this goal, the company would have needed to hire 10 to 12 additional technicians for hand soldering operations. The high cost of hiring and training these new technicians, in addition to the ever-present issue of quality consistency, led management to consider automating the soldering process, and purchasing an automated selective soldering machine.* Their system is at the lower end of the selective soldering machine cost spectrum, and, with options, cost a little above the average $55,000 basic unit.
Since the installation in March 2007, Onset has experienced a 20% improvement in productivity. The jump in the number of assemblies processed since the machine went on-line is shown:
March (partial month, machine start-up): 3986 assemblies processed;April: 6582 assemblies;May: 8531 assemblies;June: 8075 assemblies.
"Productivity increased dramatically when we brought the selective soldering machine on-line," recalls Jack Sample, president of Onset. Sample cites three product examples wherein the cycle time for each product was shortened considerably with the new system (cycle includes board loading, soldering, inspection, and cleaning).Product A: cycle time was 1 min. 45 sec., reduced to 30 sec.Product B: cycle time of 23 min. was brought down to 4 min. 30 sec.Product C: cycle time was 27 min. 25 sec., reduced to 6 min.
The selective soldering cycle relieved the assembly operation of masking time and hand soldering. The inspection process was shortened due to fewer errors to verify and note. Touch-up time has been significantly reduced or, in many cases, eliminated. The cleaning process is shortened because this process eliminates certain residues left by previous methods. These issues are important in the ROI calculation because they constitute real savings in time, product, and consumables. It's not just about how many more boards are produced per hour; it's also about how much less rework and other downstream fixes and process steps are eliminated. Cumulatively these savings can be huge.
Case Study: Selective Versus Hand Soldering During a recent installation of a selective soldering machine at Alpha Technology Inc. in Anderson, S.C., both supplier and the new customer agreed to collaborate to collect real-time data on selective soldering** versus hand soldering, with the goal being to estimate the ROI of the machine purchased.
Following the installation of the machine and training of Alpha's chief process engineer, Tom Clawson, it was agreed to run production for an eight-hour shift to collect data. Clawson programmed the board. The supplier's engineer, Kevin Valentine, also offered multiple process tips and methods to optimize the board for the quickest possible cycle time while keeping quality and consistency as a first priority. The product was for one of their top customers and the boards were needed immediately.
The complete job consisted of 164 boards, each with approximately 300 solder points. Alpha expected to be in great shape if they could get 80 boards out. Keep-away areas were not extremely tight, but they did require a 6-mm nozzle. As a result, the comparative data is considered conservative, since a larger nozzle would allow a faster run time, according to Valentine.
Alpha and their supplier had discussions with three individuals who had all hand-soldered this particular board. The quickest time offered was thirty minutes, under the best circumstances. After setup and programming the machine, Valentine was able to reduce the complete runtime on the board to 4 min. 34 sec.
"They normally assign between four and eight people to this project depending on how quickly they need to turn the job around. In this case, they would have used four people to hand solder these boards in two days with normal 10-hour shifts (80 hrs). I was unable to obtain qualified data on yields from the hand soldering process. However, the quality personnel told me they normally have a lot of touch-ups and inconsistent solder joints after inspection," summarized Valentine. Using the selective soldering machine, Alpha completed 80 boards in an eight-hour shift. The machine requires one operator, so eight labor hours for the 80 boards off the selective machine as compared to the estimated 40 labor hours for hand soldering, 5× faster.
ROIFigures 1 and 2 are print-outs of selective soldering cost analysis calculators with actual customer data and price information plugged in. It can be seen that the five-year cumulative cost to employ eight hand soldering technicians is estimated at $1,664,000, whereas the cost to operate the selective soldering machine is estimated at $263,000 however the selective soldering machine produces twice the throughput of the eight technicians (Figure 1).
Similarly in Figure 2, and in both cases we are looking at a $55,000 machine with the cost amortized over five years. Annual savings in labor are estimated at $61,000, or $305,000 over five years, based on four hand-solder operators.
Selective soldering increases productivity while cutting labor costs dramatically. Thus, the ROI for a selective soldering machine comes quickly. In addition to the benefits of higher productivity and more consistent product quality, less touchup and rework time is required. Assemblies are completed faster and at a fraction of the cost. Additionally, the customer's ability to automate the process has brought greater consistency to the resulting solder connections, since the quality of the connection is no longer dependent on operator skill and variability.
* KISS-104 from ACE Production Technologies.** The case study at Alpha was carried out with ACE's KISS-102 machine.
Alan Cable, president, A.C.E. Production Technologies, may be contacted at 3010 N. First St, Spokane Valley, Wash. 99216; (509) 924-4898; Cell: (509) 993-6571; acable@ace-protech.com; www.ace-protech.com.