ELSEVIER Surface and Coatings Technology 74-75 (1995) 770-780

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PVD equipment design: concepts for increased production throughput

Paul Stevenson, Allan Matthews Research Centre in Smface Engineering, University of Hull, Hull HU6 7RX, UK

Abstract

It is now widely accepted that plasma-assisted PVD coatings have their strongest foothold in application sectors for which throughput is low and for which coated components have high added value, such as the aerospace industry. These sectors are typically supplied by batch-type coating facilities. This suggests that there is an important gap in the market, i.e. the low cost components found in high volume industries. This has prompted a design study of PVD coating equipment. Predictions are made for the number of selected components which a typical batch production system can process in a given thne and the costs associated with that system. An estimation of throughput for a continuous system which has the same size of process chamber as the batch system is also Nven, and a comparison of the cost per component is made for each. A breakdown of the costs is given for the manufacturing and running of both batch and continuous systems. This is then used to highlight the areas where costs can be reduced in the design and manufacture of continuous coating plants.

Keywords: Physical vapour deposition; Continuous; Equipment; In-line; Coatings

1. Introduction

Advances in surface coating and treatment technol- ogies using vacuum plasma-based techniques will continue to play an important roie in breaking the technological barriers associated with surface-initiated problems. In many cases, improved product performance cannot be achieved without this "enabling" technology; this is especially the case within the automotive sector, where further developments of engines are constrained by the surfaces within them. German industry has recog- nized its importance; Volkswagen are reported to have stated that "With modern design and quality assurance techniques we can now manufacture bulk components for which their in-service performance and reliability can be specified with a high degree of certainty. However, the performance of our next generation of engines will therefore be critically dependent on a few hundred square centimetres of surface .... " [ i I .

A market study has shown that plasma-assisted PVD (PAPVD) processing only accounts for less than £15 million or a 0.5% share of the total UK engine- ering coatings industry, which is worth around £3.4 billion per year [-21. This share is predominantly in application sectors with low component throughput and high added value. The coatings needs of these applications are typically met by batch-type production

systems, which are ideally suited to low throughput requirements.

So that the total engineering coatings market may be further penetrated by plasma processing, it is foreseen that applications sectors, such as the automotive sector, will need to be satisfied in terms of process equipment design, process economics and component economics (such as the need to use cheaper substrate materials [3]). These types of industries require high component throughputs, often in excess of hundreds of thousands per year. While batch systems can cope with these demands when components are small (e.g. fuel injector parts), larger components limit batch sizes and extend the time needed to coat such components in large quantities. Although this latter demand may be met by installing further batch production systems, the capital cost of such installations may make this multiple- batch processing approach economically non-viable, i.e. the added cost to the component is too high to be introduced into an industry where it is unacceptable to the customer, in this case increasing the purchase price of an automobile. Utilization of continuous or in-line systems is one possible solution to this economic problem, but the decision whether or not to move away from batch-type systems very much depends on the geometry and size of the components and the required throughput.

0257-~972/95/.~09.50 © 1995 El~evier Science S.A. All r~eht~ reserved

P. Stevenson, A. Matthews/Szoface and Coatings Technology 74-75 (1995) 770-780 77I

2. Coatings within the automotive industry

The importance of plasma-assisted treatment tech- niques has been reported by several automobile manufacturers. The French automotive industry has taken a positive stance on promoting the technology. A large-scale plasma nitriding facility has been set up at an engine plant near Lille, supplying V6 engines to Peugeot, Citroen and Renault [1].

As yet, the automotive industry makes little use of plasma-assisted coating techniques. The high perfor- mance sector is the only major user of the technology, this being predominantly for competition use, e.g. fia Formula 1 motor racing, where many components are coated with titanium nitride (TIN) to enhance the wear performance and fatigue life, and reduce pick-up and stickSng of components such as hubs, fasteners, brake pistons and other hydraulic parts [4]. Few examples of PAPVD coatings for passenger cars are available.

One continuous production coating system for auto- motive parts has been reported from Japan; an in-line arc ion plating (AIP) system [5]. The system is claimed to achieve a production throughput of 10-40 cycles per day and was originally developed for deposition of a 3 gm TiN coating. The currently reported use for this system is CrN coating of compressor parts for car air-conditioning systems.

The system consists of four chambers, isolated by gate valves, which independently perform pumping down, pre-heating, coating and cooling. The chambers allow a maximum size of component of 400 mm wide, 700 mm deep and 100 mm high; hence, the compressor compo- nents were mounted in multiples on a 400 mm x 700 mm pallet. Total production is reported to have exceeded 5 million pieces over a period of 3 years.

The AIP system has also been used to coat titanium connecting rods with CrN. This has the advantage of providing the titamum with improved wear performance, a similar strength to existing steel rods, improved fatigue l~e with a 30% weight reduction and an increase in engine speed of 11.7 rev s -z. The coating also acts to stop wear and seizure of the crankshaft thrust surface. It is reported that this product is used in the high performance engines of commercially produced cars.

Other PAPVD coatings for the automotive sector have been reported; however, they have not been produced on a mass production basis but, generally, as one-off research test pieces. Tungsten-carbon layers (W-C:H) have been deposited using a Leybold Z700 PVD system (for Mercedes Benz AG) on steering axles made from a case carburized 20MoCr4 material [6]. The same system was used to deposit Cr/W-C:H layers with a layer thickness of 3 ~m on chain studs used in automotive handling equipment. These coatings are also suitable for rocker gear and valves, to improve friction and wear properties [7]. Their use has also been

reported on journal bearings, ball beatings and gears [8,9].

3. Design study

3.1. Selected component

In the work reported in this paper, a typical auto- motive component (i.e. a journal beating shell) was chosen to act as the development object around which deposition equipment conceptual designs could be created and assessed. The coating chosen was of the multilayer metal carbide/diamond-like carbon type referred to above.

The likely throughputs for coating a typical journal bearing shell have been predicted for batch and in-line continuous systems which have the same size of depos- ition chamber. The prediction is comparative between batch vs. continuous and shows the dependence of the component throughput on the deposition time. The prediction for the batch-type system is based on a typical commercially available sputtering system which has two magnetrons in an "opposed" configuration. This layout was chosen for this exercise, because it has been shown to produce a more uniform plasma than the four- magnetron system and is unencumbered by current patent posturing, having been described in the 1980s (see, for example, Refs. [10-12]). Also, a two-magnetron system is more conveniently adapted to continuous processing, because only two faces of the chamber are occupied by targets. The continuous system throughput is based on an in-lLne system which has chambers of equal size, each carrying out a single process operation (five ha total) similar to the batch system, i.e. (i) pump down, (ii) glow discharge and heating; (iii) ion etching, (iv) coating and (v) cooling and venting. The typical size of the bearing to be coated in these predictions is a half- shell of radius 25 mm and width 20 mm, (see Fig. 1).

3.2. Evaluation of throughput from a commercial batch system

There are many commercially availabie sputter coat- ing systems on the market, wNch will typically have a

~ 5

i

~ - ~ ; ~; ~ ~ Coated

:2 2"~<-;j -q~.-~

], 20 J

Fig. 1. Schematic diagram of journal beanng.

772 P. Stevenson, A. Matthews/Swface and Coatings Technology 74-75 (1995) 770-780

vessel height of 1000 mm [13] and a target-to-target distance diagonally across the chamber of 1000 mm. A system of this size will typically utilize targets of size 600 mm x 190 mm, which will permit an effective coating length of about 450mm, providing a layer thickness uniformity of _+ 10% [14].

If a substrate holder which has six rotating satellites and operates with dual planetary motion is used, simple geometric analysis shows that it is possible to mount up to 10 journal bearings at the same height around one satellite adapted to allow a maximum size, still fitting within the working zone specified. Simple jig design allows a number of bearings to be easily stacked on top of each other, in this example, 22 bearings can be stacked within the effective coating zone height of 450 mm (i.e. each satellite can be jigged to hold 220 bearing shells).

This aIlows for the effective coating of a total of 1320 bearings, utilizing all six satellites. The jigging arrange- ment is shown in Fig. 2.

3.3. Throughputs per shift: batch and contimtous systems

Theoretical throughputs are calculated for a shift of 8 h. For batch processes, the time for each process cycle is dependent on the loading and unloading time, pump down time, heating and etching time, deposition time, cooling time and venting time. If a continuous system incorporates all these process stages in-line (similar to the concept design shown in Fig. 3), the throughput rate, once the machine is in full production, is determined by the process stage that takes the longest time to complete. For the typical commercial batch system shown here, it

I

,a, .......... o180 H j "

I i ii

(b) (c)

Fig. 2. (a) Jigging arrangement utilizing substrate holder with six satellites in dual planetary motion: (b) top view of one satellite; (c) side view of one satellite.

P. Stevenson, A Matthews/Szoface and Coatings Technology 74-75 (1995) 770-780 773

Electrical feedthrough

"0' Ring sealing system '%. ,

Electrical ~ " feedthrough

+t-

Electrical contact

chamber

Components out

7 Rollers

chamber

7

-treatment

• J F - I

Pre-loaded / ..... ! 11 J :' I inner component [ " - - - . ~ ~ .,J I chambers in Moving rollers ~ ii Modular ci~amber

or other transport <; units, each with its system ' Chamber own pumping set

supports

!i Inner chamber with cut-outs

~:i :ii iT allow material Non-contact entry from bushing type evaporation source seals allow speedy component chamber transfer

The modular system consists of a series of inner chambers pre - loaded with components and transported through outer vacuum chambers. The inner chambers push each other through the sequence of process stages

Fig. 3. Concept for in-line continuous coating system, The modular system consists of a series of inner chambers preloaded with components and transported through outer vacuum chambers. The inner chambers push each other through the sequence of process stages.

is estimated that loading and unloading will take approx- imately 10 rain each, pump down 30 min, heating and etching 30 rain, deposition 60-180 rain (depending on the coating properties and thickness required) and cooling and venting 40 min. This estimation means that, for the batch process, the cycle time is 120 min plus 60-180rain for deposition. Deposition is the longest stage during the process, so the cycle time or time for

one throughput load for the continuous system is equal to the deposition time.

On loading the previously estimated quantity of bear- ings per cycle for the batch system, i.e. per "throughput" for the continuous system, an estimation of the number of components coated per shift can be made. Table 1 shows this estimation. It can be seen that, for a minimum deposition time of 60min, if the number of process

Table 1 Estimated number of bearings coated per shift of 8 h by a typical commercially available batch coater, compared with the theoretical number predicted for an in-line continuous system

Deposition time (rain)

Batch processing Continuous processing

Process No. of Total no. of No. of Total no. of Process No. of Total no. of No. of whole Total no. of time cycles components whole components time throughputs components throughputs components (min) per shift per shift cycIes per per shift (min) per shift per shift per shift per shift

shift

60 75 90

105 i20 135 150 165 180

180 2.7 3520 2 2640 60 8.0 10560 8 10560 195 2.5 3249 2 2640 75 6.4 8448 6 7920 210 2.3 3017 2 2640 90 5.3 7040 5 6600 225 2.1 2816 2 2640 105 4.6 6034 4 5280 240 2,0 2640 2 2640 120 4.0 5280 4 5280 255 1.9 2485 1 1320 135 3.6 4693 3 3960 270 1.8 2347 1 1320 150 3.2 4224 3 3960 285 1.7 2223 1 1320 165 2.9 3840 2 2640 300 1.6 2112 1 1320 180 2.7 3520 2 2640

774 P. Stevenson, A. Matthews/&ofaee and Coatings Technology 74-75 (1995) 770-780

cycles is rounded down to the nearest whole number, then the continuous system is capable of coating four times as many bearings as the batch system.

Table 3 Costs involved in manufacturing with a continuous system

Component Estimated Cumulative cost (£) cost (£)

4. System economics

The cost of coating a component depends upon factors such as capita1 investment, interest rates, personnel and operating costs and the component throughput. Each of these are considered below.

4.1. Capital investment

4.1.1. Batch systems Small commercial batch systems generally cost in the

region of £170000 to £300000 [15]. It is estimated that a system typical of the one described here for coating bearings would cost around £141000 to build in-house, if the constituent parts were purchased as complete units. An estimated breakdown of this cost is shown in Table 2. This cost would be considerably higher if purchasing a turnkey installation.

4.I.2. Continuous systems An estimation of the cost of building a continuous

system in-house, based on the concept shown in Fig. 3, is around £352 000. The breakdown of this cost is shown in Table 3. The costs of the magnetrons, power supplies substrate power supplies and process control systems and computers are virtually unchanged, because these are also utilized in the batch system. The major additional expenditure is in the costs associated with additional chamber sections, pumping sets, gauges, com- ponent transfer systems and load locks.

Table 2 Costs involved in manufacturing with a batch system

Component Estimated Cumulative cost (£) cost (£)

Chamber 30 000 30 000 Pumping set 20 000 50 000 Gauges 3000 53 000 Gauge controllers 3000 56 000 Magnetrons 16 000 72 000 Magnetron power supplies (4) 24 000 96 000 Substrate bias supply 10 000 106 000 Process control (OES, computer, 20 000 126 000 interface cards, etc.)

Other 15 000 141000

Total 141000

Chamber 125 000 125 000 Pumping set 100 000 225 000 Gauges 15 000 240 000 Gauge controllers 3000 243 000 Magnetrons 16 000 259 000 Magnetron power supplies (2) 24 000 283 000 Substrate bias supply 9000 292000 Process control (OES, computer, 20 000 332 000 interface cards, etc.)

Component transfer system/ 10 000 342 000 jigging

Load locks 10 000 352 000

Total 352 000

4.2. Running costs: batch and continuous

The total cost of running a PVD system is determined by the amortized capital cost (depreciation) and interest charges, personnel and operating costs, and throughput. Throughputs and capital costs have already been dis- cussed. We will take as an example interest charged at 10% per annum and depreciation over 10 years [ 15,16]. This means that the yearly interest charges will be £14000 and £35200, respectively, for the batch and continuous systems. Also, depreciation will be £14100 and £35 200, respectively, for the batch and continuous systems.

Personnel costs are shown here, based on both systems running on a three-shift basis. The batch system is assumed to require two operators continuously (one equipment operator, one cleaning and jigging, and both loading and unloading) and the continuous system three operators continuously (one equipment operator, one jigging and loading, and one unloading and stacking). Assuming for both cases that the machines are run for 240 working days of the year, then the total man-hours for 1 year are 11 520 and 17 280 for batch and continuous processing respectively. If 1 man-hour is costed in at a typical rate of £15 per hour (including a partial overhead cost), then the yearly costs are £172 800 and £259 200 respectively.

Operating costs include maintenance (which is esti- mated at 3% of the capital cost), electricity, water, factory floor space and consumables, such as gases and target materials. Electricity costs are based on £0.0415kWh -1, water on £0.541m -3 and space on £80 m -2 per year. Target costs for titanium of dimen- sions 600 mm x 50 mm are approximately £250-£800 each, depending on purity, thickness, time of order and quantity. In this example, titanium targets (99.9%) are costed at £576. A full breakdown of all the associated costs is shown in Tables 4-8. Table 4 shows the fixed

P Stevenson, A. Matthews/Smface and Coat#zgs Technology 74-75 (1995) 770-780 775

Table 4 Fixed overhead costs for batch and continuous systems

Batch processing Continuous processing

Capital investment and associated costs Capital investment (£) 141000 352 000

(inc. installation) Depreciation a (£) 14100 35 200 Interest charges b (£) 14100 35 200 Total capital investment 28 200 70 400

per year (£)

Staff and maintenance costs Shifts per day 3 3 Working days per year 240 240 No, operators required 2 3 Total no. man-hours 11520 17 280

per year Total man-cost ° (£) 172 800 259 200 Maintenance as 3 3 percentage of capital (%)

Maintenance costs (£) 5400 11760

a Based on 10 years of depreciation. b Based on interest rate of 10%, ° Based on hourly rate per man of £15,

costs associated with capital investment and staffing; Tables 5-7 show the variable costs associated with target utilization and consumables; and Table 8 shows the total running costs and the cost of coating a single component.

The component cost vs. the number of components processed per year is plotted in Fig. 4 for a fixed depos- ition time of 60min for both batch and continuous systems. Fig. 4 shows the use of up to three batch systems to process the same number of components as the maximum for the continuous system.

4.3. Costs per component, batch vs. continuous

If the deposition time is kept constant, then the cost per component increases as the number of components coated decreases from the maximum theoretical through- put. This is shown in Fig. 4, where the cost per compo- nent is plotted against the number of components coated per year for a fixed deposition time of 60 rain. For batch production to equal the maximum for the continuous system, three production machines are necessary; these are indicated by the three portions of the batch process- ing curves on the graph. For this graph, it is assumed that the second batch system is not purchased until the production requirements are greater than the maximum throughput for one system and the third system is not purchased until the production requirements are greater than the maximum available from two systems.

The graph shows that, up to 2534400 components per year, the batch system is more cost effective than the continuous. In this region, when the batch system is running at its maximum throughput, the cost per compo- nent is £0.117 compared with £0.220 for the continuous system. Any subsequent coating of components in the batch processing environment then has to be carried out in a second batch system. Between 2 534 401 and approx- imately 3 000 000 components per year, the batch system is not competitive with the continuous system, with the cost per component rising above £1.00. When the maximum throughput for the second batch system is approached, the cost per component once again approaches £0.117 and equals that of the continuous system. If three batch systems need to be used, i.e. to coat more than 5068 800 components, then the batch system is no longer competitive with the continuous

Table 5 Variable costs for batch and continuous systems: target utilization

Deposition Utilization time (no. cycIes (rain) per target)

No. runs per shift No. targets used per year

Batch Continuous Batch Continuous processing processing processing processing

Cost per target (£)

Total cost of targets per year (£)

Batch Continuous processing processing

60 75 9O

105 120 135 150 165 I80 195 210 225 240 255 270 285

25 2.7 8.0 153.8 2.5 6.4 141.8 2.3 5,3 131,7 2.1 4,6 122.9 2.0 4.0 115.2 1.9 3.6 108.4 1.8 3.2 102.4 1.7 2.9 97.0 1.6 2.7 92.2 1.5 2.5 87.8 1.5 2,3 83.8 1.4 2.1 80.1 1.3 2.0 76.8 1.3 1.9 73.7 1.2 1.8 70.9 1.2 1,7 68.3

460.8 576 88 474 265421 368.6 81 668 212 337 307,2 75 835 176947 263,3 70 779 151 669 230.4 66355 132710 204.8 62452 117965 184.3 58982 106168 167,6 55 878 96 517 153.6 53 084 88 474 i41.8 50 556 81 668 131,7 48 258 75 835 122.9 46 160 70779 115.2 44237 66 355 108.4 42467 62452 102.4 40834 58 982 97,0 39 322 55 878

776 P. Stevenson, A. Matthews/Swface and Coatings Technology 74-75 (1995) 770-780

Table 6 Variable costs for batch and continuous systems: consumable costs (dependent on deposition time)

Deposition Electricity for utilities Electricity for deposition Electricity costs time per year (kWh) per year (kWh) per unit (£) (min)

Batch Continuous Batch Continuous processing processing processing processing

Total electricity costs per year~)

Batch Continuous processing processing

60 40000 75000 4800 75 5538 90 6171

105 6720 120 7200 135 7624 150 8000 165 8337 180 8640 195 8914 210 9164 225 9391 240 9600 255 9792 270 9969 285 10133

14400 0.041 1836.80 3665.40 1867.08 1893.03 1915.52 1935.20 1952,56 1968.00 1981.81 1994.24 2005.49 2015.71 2025.04 2033.60 2041.47 2048.74 2055.47

Table 7 Variable costs for batch and continuous systems: consumable costs (independent of deposition time)

Batch Continuous processing processing

Water (m 3) 50 80 Cost per unit (£) 0.541 0.054i Total water costs (£) 27.05 43.28 Space requirements (m 3) 10 18 Cost per cubic metre (£) 80 80 Total space cost (£) 800 1440

system. At m a x i m u m throughput , the con t inuous system

costs £0.081 to coat a c o m p o n e n t c o m p a r e d with £0.117

for the equivalent three ba tch systems,

Fig. 5 shows a similar set of results, but, this time, it

is k n o w n if one, two or three ba tch systems are required

at the beginning of p roduc t ion planning, i.e, the costs

associa ted with mul t ip le -ba tch processing are evenly

d is t r ibuted from coat ing of the first item. The graph

shows as before tha t the cost per componen t up to a

m a x i m u m th roughpu t of 2534400 for a single ba tch

system is less than that for cont inuous product ion .

U p to 5068800 componen t s per year, the cost per

Table 8 Cost per component for batch and continuous systems compared with deposition time

Deposition time (rain)

Total running costs per year (£) No. components coated per year Cost per component (£)

Batch Continuous Batch Continuous Batch Continuous processing processing proccessing processing processing processing

60 297 167 612329 2 534400 7 603 200 0.117 75 290392 559 245 2339446 6082560 0.124 90 284584 523 855 2 172343 5068 800 0.131

105 279 551 498 577 2027 520 4344686 0.138 120 275147 479619 1900800 3801600 0.145 135 271 261 464 873 1 788 988 3 379200 0.152 150 267 807 453 077 1 689 600 3 041280 0.159 165 264716 443 425 1 600674 2764800 0.165 180 261935 435 382 1 520640 2 534400 0.172 195 259418 428 576 1448 229 2339446 0.179 210 257 131 422743 1 382400 2 172 343 0.186 225 255042 417 687 1 322296 2027 520 0.193 240 253 127 413 263 1 267200 1 900 800 0.200 255 251 365 409 360 1 216 512 1788988 0.207 270 249 739 405 891 i 169 723 1 689 600 0.214 285 248234 402786 1 126400 1 600674 0.220

0,081 0.092 0.103 0.115 0.126 0,138 0.149 0.160 0,172 0.183 0.195 0.206 0.217 0.229 0.240 0.252

P. Stevenson, A. Matthews/Smface and Coatings Technology 74-75 (1995) 770-780 777

1 I

0.80 I I Centinuous System _ [ o 8 5 - - I I

0.80 0.75 I 0.70 0.65 '-'i:3'-' B arch ]

~" I -"~-'Continueus J ~" 0.60

t obo l 1 O Two Batch Systems Three Batch Systems I

I

0.10

0.05.

0.00 1 0 500000 1000000 1500000 2000000 2500000 3000000 3500000 4000000 4500000 5000000 5500000 6000000 6500000 7000000 7500000

No, of Components Coated per Year

Fig. 4. Cost per component vs. number of components coated for batch ([~) and continuous (A) systems, assuming purchase decisions on second and third batch systems are only made once the first and second systems are fulIy utilized.

1.800

1.600 t

1.400

1.200

' I i 1.000

o I ~. 0 . 800 - -

0.600 ~

0 . 0 0 0 . , ,

No, of components coated

, - o I One batch system i-"O'-Two batch systems '-'~IThree batch systems ~Continuous sys ern

Fig. 5. Cost per component vs. number of components coated for one (O), two (rT) and three (A) batch systems and continuous (<5) systems, assuming the batch systems are bought at the same time as the continuous system.

component when utilizing two batch systems is negligibly higher than that for the continuous system. The con- tinuous system is more cost effective than utilization of three batch systems.

Calculations of the cost per component for batch and continuous systems which have the same size of chain-

bers have been carried out with varying deposition time, because this appears to be the rate-determining step within the continuous system. Table 8 shows that, for both batch and continuous systems, as the deposition time increases (from 60 to 285 min), the cost per com- ponent also increases. If the maximum throughput is

778 P Stevenson, A. Matthews/Smface and Coatings Technology 74-75 (1995) 770-780

0.275

0.250

0,225

0.200

0.175 ,.---

0.100

01075

M jf

~=¢mBatc h '~3BCon inuous

0.050

0.025 I

0000 J , 60 75 90 105 120 135 150 185 180 195 210 225 240 255 270 285

Deposition Time (mins)

Fig. 6. Cost per component vs. deposition time for batch (~) and continuous (D) systems (assuming maximum throughput).

maintained for both systems, a point is reached at which the deposition time becomes sufficiently high to make the batch system more economical than the continuous system. It can be seen that this occurs when the depos- ition time is more than 80 min in this instance. This is shown graphically in Fig. 6.

4.4. Reducing capital investment and costs per component

From Tables 4-7 it can be seen that the major costs of running a continuous system are from capital invest- ment and target utilization. The capital (and associated) costs and target costs are approximately £88474 and £265 421 per year respectively. So that continuous pro- cessing can become more effective, costs in these areas need to be reduced.

Fig. 7 shows how the cost per component varies with target utilization, i.e. how many cycles can be completed before target replacement becomes necessary for a fixed deposition time of 60 min per cycle. It can be seen that doubling the cycles from 25 to 50 per set of targets reduces the cost per component by approximately £0.076. A further increase of 50 cycles, i.e. 100 complete cycles per set of targets, reduces the cost by a further £0.006 per component, and an increase to 200 cycles reduces the cost by a further £0.0074 per component over this. For this particular example, as the number of cycles per set of targets increases, the cost per component is decreased, as expected, but this decrease has less of an impact. The overall decrease in the cost per compo- nent is £0.0284 when the target utilization is multiplied by eight from 25 cycles per set of targets to 200. This

applies for both the batch and the continuous systems, with the cost per component being consistently lower with the continuous system.

To minimize capital investment in equipment, the associated materials and manufacturing costs need to be reduced. Critically evaluating system design by splitting the system down into "°part" design areas and assessing these areas in terms of design for manufacture potentially allows equipment to be produced at lower cost. Work in this field currently includes the following areas for evaluation: chamber design and fabrication; component jigging; component transfer mechanisms; and source design.

Fig. 8 shows a plot of the cost per component vs. the capital cost for both the batch and the continuous systems. Although a reduced capital cost reduces the cost per component, this graph shows that, even if the capital investment for continuous equipment manufac- ture is increased from the £352000 in this example to £1000 000, the cost per component increases from £0.081 to £0.0975, but is still below the cost per component for batch processing, i.e. below £0.117.

5. Conclusions

The economics of batch vs. continuous systems are complex, and the cost effectiveness very much depends on the type and quantities of components to be coated, and on the deposition technique adopted, deposition time and "floor-to-floor" cycle times. The example shown here is theoretical but illustrates that there will generally

P Stevenson, A Matthews/Smface and Coatings Technology 74-75 (1995) 770-780 7 7 9

0.12

0.11

0.1

~c

8. 0.09

o

0.08 "S

0.07

I I i I

1 I I

I

'~[::l'"C o n nueus

o.os , 50 78 100 125 150 175 200

No. of Cycles per Target

Fig. 7. Cost per component vs. target utilization (number of cycles per target) (deposition time 60 rain): ~, batch system; cq, continuous system.

0.128 I I I I I I t

I ! I t I 1 1 - -' I - T - t 0,115

0.105 I I I

I 8

I I

t T , 0.085 ~ , ..1- ~

0.078 ~ I I

o o68 ' I p

I I I

I l I

Capital Cost (£)

I~ Batch 1 ConUnuousJ

Fig. 8. Cost per component vs. capital cost of continuous processing equipment (deposition time 60 rain): A, batch system; [Z, continuous system.

be some cut-off point where continuous systems become more cost effective than batch processing. In order that PAPVD coatings may penetrate high throughput industries similar to that identified, i.e. the automotive industry, reduced costs commensurate with this type of volume industry will need to be achieved. These will almost certainly come from the advent of continuous

systems, where the exact nature of the required coating and substrate is known.

The predictions of the component costs are based on zero system downtime resulting from breakdowns and maintenance during the 240 working days; i.e. all mainte- nance is preventative and is carried out in specified shutdown periods outside of the 240 processing days. In

780 P. Stevenson, A. Matthews/Swface and Coatings Technology 74175 (1995) 770-780

practice, this is not usually achieved, so we are carrying out a comprehensive study on the reliability of systems. This enables a prediction of individual system com- ponent failure and allows maintenance intervals to be scheduled optimally, so reducing unexpected downtime. Mean times to failure, repair times and a ranking order of system component criticality are being compiled, highlighting those areas of the system that need to be scrutinized more closely. However, it must always be remembered by those making a choice between "batch" or "continuous" that the penalties of the breakdown of the continuous system will be much greater than those for a breakdown of one or even two of the batch systems, because some production could still be maintained with the running batch system(s).

In order that continuous systems can become more economically viable, it is important that their design is critically assessed to reduce equipment materials and manufacturing costs, while maintaining system flexibil- ity. In the case of magnetron sputtering systems, the major running expense in our calculations is that associ- ated with target utilization and cost. Reducing this cost, along with that associated with capital investment, reduces significantly the cost per component. However, in this example, significant increases in these costs still show continuous processing to more economically viable.

Acknowledgements

The authors thank all their colleagues at the Research Centre in Surface Engineering at Hull for helpful discus-

sions, especially Adrian Leyland. We also wish to record our thanks to the UK Engineering and Physical Sciences Research Council for providing financial support.

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