Divining Value in Screen Printer Ownership Print E-mail
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Written by Trevor Warren   
Thursday, 01 April 2010 00:00

Companies return to market with new requirements, fresh capital, and new ways to evaluate cost-of-ownership. 

 

Value can be defined in many ways. In a financial sense, value is how much of what you need you actually get for your money. But measuring “how much you get” is not straightforward. It’s easy to confuse cost with value. Low cost does not automatically translate to the best value. Likewise, the highest price isn’t necessarily the best value. The purchase price of a capital item is only one element of value, but it can be one that is disproportionately influential in the purchase decision. A useful automotive analogy can be drawn here.

For most individuals, a car is among the largest capital purchases, or investments, they will make. Will the cheapest car represent the greatest value? The costs of running and maintaining a car need to be taken into consideration to determine a better measure of value. Then there’s the issue of the value of the car when the owner has finished with it. Leasing companies know this because their long experience and amassed statistical data have turned whole-operational-life value into a science. It’s why the monthly lease price of different vehicles is not directly proportional to their forecourt purchase price.

In principle, the same is true in industrial capital equipment. But all too often, the potential end-of-life value of a capital purchase is not taken into account. Could it be because it’s more difficult to identify the use to which the equipment may subsequently be put? Or perhaps because there’s no guide to look up the likely fiscal worth of used equipment? The experience of most electronics assembly capital equipment vendors is that investment in new equipment is typically justified on the basis of a single manufacturing requirement or contract, or at least an identifiable operational run lasting a few months to a couple years. Equipment needs to pay for itself easily within a percentage of that period to deliver a financial return. Understandably, the shorter the identified operational run, the more critical the initial purchase price of equipment seems to be to the purchase decision. But often this is a false economy.

A few years ago, one of the industry’s leading surface mount pick-and-place equipment vendors ran studies into the equipment investment its larger EMS customers were making as a proportion of its total outlay to resource each new contract they secured. The result was usually around 2.5%. (The largest single portion of every contract investment was the procurement of components.) Within a typically conventional SMT assembly line comprising printer, placer and reflow oven, the placement machines invariably represent the largest part of the investment – accounting for around 1.5% of the 2.5%. Allowing for the oven, this means less than 1% of the total investment goes toward the screen printer. At less than one-hundredth of the overall investment funding, a few percent variation in the purchase price of a screen printer is relatively insignificant compared to what return the right equipment can deliver – or the horrors of what it may cost if it doesn’t deliver.

Which is why, for these large EMS companies, the value of the printer – measured in terms that include less tangible elements like on-time delivery, service support responsiveness, applications expertise, fast ramp to productivity, maximized uptime, etc. – is always more critical than the initial machine cost.

Not all screen-printer users are large EMS providers after lucrative new contracts. But all manufacturers can improve printer ownership value by considering a few strategic points when specifying the equipment.

‘Flawless balance’ challenges. Screen-printer productivity is a combination of throughput and yield. Conveying the maximum number of good printed boards from the print platform to keep downstream processes operating at peak efficiency is the productivity goal. But getting a flawless balance between throughput and yield is a challenge; there’s no point in speeding the print process if yield suffers. Screen printing still has the most potential of any process in the assembly line to introduce catastrophic faults.1,2 A single unprinted pad, if undetected, can render a subassembly useless or incur significant cost in diagnosis and rework. Or both.

The temptation to ramp throughput by, for instance, reducing cleaning cycle frequency or increasing squeegee excursion speed can lead to lower yields as the process moves out of control. So many variables influence the process that deploying expert knowledge is the best way to keep control. Dr. Ron Lasky of Dartmouth College, a leading Six Sigma process expert, illustrates aspects of process control in the screen-printing domain using a fictional process expert (“The Professor”) who investigates manufacturing issues, and who – as a profit sleuth – often focuses on COO as he helps electronics assemblers recover lost profit.
In one of The Professor’s investigations,3 Dr. Lasky cites the overall losses incurred by a manufacturer from switching to a cheaper solder paste. The production engineering manager’s expectation is to save more than $30,000 per line per year by using paste costing only 5 cents per gram, as opposed to 8 cents per gram.

But the paste has one property weakness in the form of lower on-screen open life, so each board printed after a stoppage must be cleaned and reprinted because the paste has “stiffened” – an exercise that costs 20 minutes in lost production per line per day, and which, with the production run figures in the example, results in a cost burden of over $340,000 per year. It’s presented as fiction, but the impression is that it’s not. In any event, it illustrates exactly the kind of process variable that requires specialized expertise to fully evaluate and manage.

Operational cost-of-ownership. Another obvious way to reduce, or at least contain, the cost associated with running a screen printer is to ensure the system is paying its way all the time – or as close to that as is practical. Downtime is the enemy of productivity. And productivity often relates directly to profitability.

Downtime comes in many forms, most predictable and therefore manageable. Even unscheduled stoppages often result from operator oversight or error, or from a process or material issue, and in theory can be legislated against.

Scheduled stoppages for consumables replenishment and planned downtime for maintenance are both areas worthy of scrutiny. Choosing a printer that has fewer maintenance intervals, or that offers easier access to permit maintenance to take place faster, will render it offline for less time, which equates to better value when measured in terms of productive uptime. Solder paste replenishment is a frequent and necessary intervention, so rapid and easy access to the print area that lets this procedure take place more quickly has a true value that reduces COO by keeping the printer productive.

In addition, simple actions like selecting the optimum consumables for production needs can improve productivity. A recent study of understencil cleaning fabrics reveals not only measurable differences in the cleaning effectiveness of materials, but disparities in the length of the fabric rolls for a given price.4 Naturally, the longer the roll, the less often the printer will need to halt for replenishment. Equipment manufacturers may offer a number of equipment options on printer platforms that mitigate stoppages, from effective cleaning fluids, fabric rolls and operator alerts to sophisticated tools such as paste height monitors and high throughput understencil cleaning.

The latter is a case in point on the issue of cost versus value. Newer generation systems have cleaning excursions that take half the time, use less than half the quantity of understencil cleaning fabric, and clean more effectively than comparable systems. They offer a choice: clean to the same standard as before, which means less frequently but more quickly to dramatically increase batch throughput by reducing the number of times the printer halts for a cleaning cycle and shortening the time it takes when it does; or clean as frequently as before, but twice as fast, to really safeguard yield and increment throughput. Clearly, both strategies have a tangible productivity value.

Another constraint on maintaining productivity is in high-mix assembly environments with high product changeover. Identifying ways to reduce the time it takes to set up the printer for a new board is key to productivity when measured over several batches, a more realistic snapshot of production. Using The Professor’s technique of calculating potential earnings when the printer and line are running to capacity determines revenue lost for every minute of downtime. Again, tools exist to assist. Small EMS providers and OEMs that run several products in short batches should look at automated tooling for board support; at self-loading and aligning stencils to speed the operation and eliminate operator errors; and be aware of the time it takes to upload or initialize the software print file.

Looking at these stoppage types prompted Dr. Lasky to articulate how a simple cocktail of screen-print process considerations can reverse an expected financial outcome. The example is a manufacturer who contemplates deploying new screen printers with a purchase price $20,000 lower than those traditionally in use onsite; the intention being to save a total of $1 million over 50 lines. The Professor’s investigations reveal how tiny time-based procedural issues that appear insignificant on their own can wipe out capital equipment purchase savings. In the example, factors such as 10% longer changeover due to more steps in setting up board support, computer programming and stencil installation, plus 15% more time to replenish solder paste, result in 3% less production, producing 3% less product, which equates to 6% less profit. On lines intended to average $4 million per year in profit, the small stoppages accumulate to lose around $240,000 per line per year, making the $20,000 saving on purchase price a gigantic false economy.

A final COO domain has traditionally remained unfulfilled. Arguably one of the greatest potential COO gains to be made is in the ability to redeploy a screen printer from production runs to other uses. Thanks to platform concepts, screen printers can be redeployed, often with no more than a modest investment in a module to reduce cycle time by two seconds, or an inspection system for traceability and higher yields.

References

1. J. Pan, et al., “Critical Variables of Solder Paste Stencil Printing for Micro-BGA and Fine Pitch QFP,” IEEE/CPMT International Electronics Manufacturing Technology Symposium, 1999.
2. K. Feldmann and J. Sturm, “Closed Loop Quality Control in Printed Circuit Assembly,” IEEE Transactions on Components, Hybrids and Manufacturing Technology, Part A, vol. 17, no. 2, 1994.
3. R. Lasky, “ ‘Paste is Paste’: The Professor Hits the Road,” Circuits Assembly blog, Oct. 25, 2009.
4. C. Ashmore, “Understencil Cleaning’s Little Devil,” Circuits Assembly, August 2009.

Trevor Warren is Americas product manager at DEK (dek.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated on Thursday, 25 March 2010 18:58
 

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