UPORABA PLAZME V ELEKTRONIKI APPLICATION OF PLASMA IN ELECTRONICS PLASMA PROCESSES PART II : APPLICATiONS IN ELECTRONICS I. Šorli*, W. Petasch, B. Kegel, H. Schmid, G. Llebel, W. Ries *MIKROIKS d.o.o., Ljubljana, Slovenia Technics Plasma GmbH, Kirchheim, Germany 1.0 INTRODUCTION Plasma Is obtained by producing a discharge in gases or gas mixtures under vacuum through the application of high frequency alternating voltage. The gas in the chamber is brought to an excited (ionized) state. As well, active radicals and UV radiation are released. Electrons and UV light, resulting from the recombination processes are essential for maintaining the plasma. These components are the actual energy carriers, which are ultimately responsible for the production of chemically active radicals. This highly active process gas is capable of reacting with the surface of the material to be treated even at low temperatures. During the process fresh gas is continuously fed into the chamber. The reaction products are evacuated by the vacuum pump. Plasma excitation via microwaves (2.45 GHz) has proved especially effective, since the efficiency of the gas discharge increases considerably with increasing frequency but still requiring very low electrical power. This results in strong, intensive ionization and production of radicals and thus a more cost effective process. Today's microwave excitation technology makes it possible to use the low pressure plasma processes economically in industrial mass production in either continuous or batch systems using large process chambers. Small bulk parts, as well as large components can be effectively cleaned and activated. Very important issue of low pressure plasma is its penetrability. The gas enters the smallest crevices, making it possible to process three - dimensional parts with complex geometries. Another very important fact is that plasma processes are environmentally friendly and as such are alternatives to CFC cleaning processes. Thus, main advantages of low-pressure plasma technology are: • dry process • energy saving through low power consumption • inexpensive supplies, cost - effective gases • switch - off chemistry: the process stops immediately when the power is turned off, no disposal of waste cleaner, safer workplace, simple operation high penetration power into narrow spaces - an advantage in degreasing or activating parts with complex shapes constant process conditions, good reproducibility meets or exceeds air emission standards parts are absolutely dry after treatment 2.0 SUPER FINE CLEANING WITH LIQUID PHASE PRECLEANING AND SUBSEQUENT PLASMA TREATMENT 2.1 GENERAL Cleaning and degreasing is a widely used industrial procedure. Stricter environmental requirements and recently discovered facts regarding the effect of previously used cleaning and drying agents on atmosphere chemistry make a radical review of the conventional cleaning technologies necessary. The plasma process is especially well suited for removing organic contaminants and residual films (such as greases, oils, waxes or solvents) when the films are very thin and super clean surfaces are required. A very important characteristic of low pressure plasma is its penetrating power. The gas penetrates into small pores that are difficuitt or impossible for liquids to access. Thus, even parts with complex shapes can be easily processed with plasma (cutouts, small radii, bore holes, slots). The penetration capability allows the plasma to reach even cracks with micrometric dimensions. Since most cleaning problems are concerned with the removal of organic substances from the surface, oxygen is used in most cases as the reactive gas. Oxygen is" so one of the most important process gases in the treatment of almost all types of materials, In the case of polymer activation which is discussed in Part ill, best results are achieved with oxygen for the most common polymers. Mechanical abrasion through particle bombardment (sputtering effect) has a subordinate role in the type of equipment used for this purpose. The effect of oxygen is enhanced by the admixture of small amounts (five to ten percent) of argon or helium. Slightly preheating the parts to between 80 and 100°C, whenever the material to be treated allows, is also helpful. Since the process gas immediately returns to its original state after the gas discharge has been shut off, possible residues capable of causing long term corrosion represent no problem. Plasma cleaning means that organic impurities are removed by chemically transforming them in volatile products CO, CO2 and H2O, figure 1. In short, the process is a dry one, no submerging of the parts into a liquid takes place and energy cost for a separate drying phase can be saved. Thus, when oxygen is used the cleaning effect consists of oxidative conversion of the organic contaminants. PLASMA ^ O,'^, 0/, 0,0*, o' clcctrons, photons organic material ( C, H, O, N,...) SURFAO^ (Chemical Reaction) Figure 1: Oxygen plasma cleaning principle 2.2 ENVIRONMENTAL PLUSES TO PLASIVIA The plasma process does not use acids, lyes, solvents or liquid halogenated hydrocarbons. The reaction with the process gas takes place in hermetically sealed chambers. For operation, this means no disposal problems and clean workplace conditions, since no poisonous gases or vapors are produced and no hazardous liquids are handled. A plasma system can be easily operated by semi - skilled personnel. The process is simple and does not require special education. Waste gas emissions satisfy and exceed TA clean air standards. There is no fire or explosion hazard. 2.3 DOWNSIDE TO PLASMA Critical examination discloses the following limitations of this process: 1. Intensive contamination is always irregularly distributed. Thus, the treatment period is long. 2. Photochemical reactions within the surface layer may lead to a crosslinking reaction of the layer material which results in a reduction in the etching rate. 3. Inorganic components (machininng chips, debris and other particles) cannot be removed. They tend to form non-volatile oxides or salts remaining on the surfaces. A solution is provided by a precleaning step, in which the inorganic components are removed and the processing agent amounts are reduced. This leaves a relatively uniform residual layer, which can be removed by means of plasma in a few minutes. 2.4 PRECLEANING WITH DIFFERENT MEDIA As discussed above, precleaning may be required depending on the initial conditions. The medium used for preclean, the material to be cleaned and the chemical composition of the contamination have an influence on the results of the subsequent plasma cleaning. In the following example, solvent in the form of glycol ether and water, are used as cleaning agents. The part must be dry prior to plasma fine cleaning. Plant design with the respective peripherals (distilling unit, water treatment and purification) are shown in figure 2. Examples and Results of Cleaning Procedures Application: Degreasing of metallic parts Case Description: Cleaning of brass, aluminum and steel parts prior to assembly Cleaning requirements: Minimum grease level (low residue carbon) Former cleaning process: Aqueous and CFC Alternative solution: Aqueous precleaning and final plasma cleaning. Results showing residual carbon (mg/cm^) left after cleaning are presented in table 1. TABLE 1 Material Aqueous Cleaning Aqueous + Tri Aqueous + Plasma X12CrNiS188 29.3 6.8 2.7 CuZn39Pb3 20.7 5.3 3.5 AlCuMgPb 19 7.5 3.7 Additionally, the good cleaning results are confirnned by quantitative measurements of the adhesion of the cleaned parts, table 2. Test setup: copper tube with 3 mm diameter, glued into an aluminum block, both suitably cleaned; glue used: Gupalon 30, setting for four hours at 120°C TABLE 2 Cleaning method Tear Strength (N) Aqueous 531 Aqueous -f- Tri 642 Aqueous + Plasma 785 Parts: Injection molded and stamped parts Material: Non-ferrous metals, silver, plastic Contamination: stripping agents, stamping and bending oils, flux Cleaning agent: Glycol ether (Zestron LP) Water: demineralized, continuously recirculating Cleaning requirements: visually spotless, greaseless, low electrical resistance, imprintability Capacity/cycle time: process - dependent Batches: 40 x 50 x 20 cm perforated baskets Floorspaoe required: approx. 40 m^ Installed power: 65 kW Figure 3: Combination wet/piasma cleaning of metal and plastic parts for the automotive industry Combination solvent/water and plasma treatment STATION 1 Cleaning ( Filter. )xida STATION 2 Rinse Filtei r UV eacto MW ■c Ion exchajnge colun I J 1st stage : Cleaning - dipping with ultrasound( glycolether) 2nd stage : Cleaning - rinsing ( DI water) 3rd stage : Drying in a forced-air oven, at 70 deg.C 4th stage : Oxygen plasma cleaning STATION 4 PLASMA MW Flof egula STATION 4 PLASMA X Flo eguli to A Gas; Gas J1 Gas; Gas Recirculation of the cleaning agent ( glycol ether ) through a particle filter, purification of rinsing water via photo-oxidation of the entrained glycol ether with hydrogen peroxide added, continuous monitoring via oxidation - reduction potential and conductivity measurement after ion exchange, temperature control in furnace, totally enclosed with central exhaust system, automatic handling, automatic process control. Other process versions are possible ( e.g. plasma only, aqueous precleaning and plasma, precleaning only, etc.) Figure 2: Combination of solvent/water and plasma treatment 3.0 APPLICATION OF PLASMA TECHNOLOGY IN ELECTRONIC PACKAGING Prohibition of CFC's and, in addition increasing surface quality requirennents make new solutions for electronic board cleaning necessary. As well, plasma applications of great interest are metal finishing prior to fluxless soldering, device cleaning for reliable wire bonding and surface treatment for adhesive bonding. 3.1 WIRE BONDING ON CRITICAL SURFACES The yield of plasma treatment is demonstrated by comparative experiments with and without plasma pre-treat-ment. Parameters of practical significance such as the strength of wire bonds are used as evaluation criteria. In particular, for bonding wires to printed circuit board substrates, bonding to the connection metal platings is a frequent source of problems. In addition to the inho-mogenity of the circuit board's matrix structure, the quality of the bond pad surface is a frequent cause of failures. Preceding process steps such as soldering and adhesive bonding cause organic contamination, which may precipitate on the bond pads, e.g. in the chip - on - board (COB) technology. With the introduction of a plasma process, prior to bonding wet chemical cleaning can be completely omitted. Wire bonds are characterized using strength tests such as the pull test according to MIL-STD 883D. Then a metallographic ground cross section of a wire bond is prepared in order to make the joint area visible. Mechanical Strength Test: Pull Test The destructive pull test (MIL - STD 883D, Method 2011) is a standard test for determining the strength and reliability of wire bonds. The wire bridge is pulled with a hook under the effect of a continuously increasing pulling force until rupture. The maximum force is measured, making sure that the individual measurements are reproducible. When evaluating the pull test, one should basically distinguish between different rupture characteristics or failure modes. We distinguish between the failure modes of bond detachment from metallization and wire rupture in the deformation zone. The different qualities of substrate surfaces can affect bond detachment, but also influence the introduction of ultrasonic energy in the bond, which leads to different kinds of wire deformation at the bond with the resulting effects on wire strength in the heel area. In figure 4 possible failure modes in the pull test are shown. A, B: Failure in bond at interface between wire and metallization (bond detachment), 1st or 2nd bond E, F: Wire rupture at the bond heel, 1 st and 2nd bond H: Bond failure: no bond was made Well defined contamination of the bond surfaces Laboratory tests were performed with well defined contamination on bond surfaces. Surface: Chemically deposited Ni/Au on FR4 substrate. Bonding process: Ultrasonic wedge bonding with 25 |j,m AlSil wire. In order to investigate the effectiveness of a plasma cleaning process, a contamination was applied which represents a real - life contamination actually occuring during electronic manufacturing. The surface contamination and its effect on bondability was tested using a reflow soldering process. The soldering paste on the substrate was melted. The flux component constituted the bond pad contamination. Prior to bonding, the substrates were subjected to plasma cleaning. Then over 100 bonded wire edges were placed on each substrate and tested with the destructive pull test. 1. Bond Figure 4: Failure modes in the puli test Plasma cleaning Two different plasma processes were used with the samples contaminated with the flux residue of the reflow soldering. The O2 plasma has an oxidizing effect on the organic deposits; the Purigon (trade name of Linde AG) plasma also has a reducing effect on the metal oxides due to the H2 component. Results and discussion Table 3 shows the results of the individual test series. The average force for all failure modes (bond strength) is given with the standard deviation a, as well as the distribution by individual failure modes, including the corresponding average force. Test series a) shows the succesful optimization in relation to the initial conditions. Bond detachment is minimized and the average force of 7.2 cN is significantly larger than the suggested value of 4.0 cN. With contaminated surfaces (series b)) the average rupture force TABLE 3 Test series F cN 0 cN Distribution (%) Average force (cN) for different failure modes Remarks A B E F H a) initial state 7.2 0.8 8,0 6,1 1,0 6,1 66.0 7.2 25,0 7,6 0 Bond optimization: A, B min. b) contaminated 5.5 2,9 24.8 4.8 6.0 6.8 35.0 7.5 15,4 7,5 17,1 Bonding results significantly inferior d^) O2 plasma 6.9 1.8 0.7 7,0 2.2 6,3 81.0 7.3 10,9 7.4 5,1 Bonding results almost as good as a). Failure modes A, B drastically reduced Purigon plasma 6.2 2.2 19.6 5.7 6,5 5,2 44.2 7.3 21,0 7,1 8,7 Improvement but clearly inferior to O2 plasma c) contaminated - with parameter optimization 6.0 2,0 38.5 4,5 0.7 9,2 28.1 7,3 29,6 7,2 3,0 No substantial improvement. Effect of contamination cannot be eliminated by parameter optimization e) O2 plasma - with parameter optimization 7.6 0.8 0 5,5 6,8 3.7 8,1 90,8 7,7 0 Slight improvement compared to d^ drops down to 5.5 oN, while the standard deviation increases dramatically to 2.9 cN. Bond detachment increases drastically, and bonding errors are also observed. This negative effect of the contamination can be eliminated by plasma cleaning in an O2 plasma. In particular, bond detachment types A and 8 disappear nearly completely. Purigon plasma is not as effective as O2 plasma, because the organic deposits only respond to oxidizing action. The main component of Purigon, hydrogen, cannot be active, but it reduces the partial pressure of oxygen. For test series c) we attempted to compensate for surface contamination by optimizing the bonding parameters. Since bond detachment A cannot be reduced below the 38.5% limits, the procedure was not successful. Thus the effect of contamination cannot be eleimi-nated by optimization only. In the case of O2 plasma cleaning, however, the subsequent optimization results in a slight improvement of the bond strength (series e)). 3.2 ENHANCE HYBRID RELIABILITY THROUGH PLASMA CLEANING Poor wire bonding is the primary cause of failure in hybrid integrated circuits. To create a successful wire bond, strong intermetallic contact between pads on a hybrid and the bond wires must be achieved. This is possible only when the two surfaces are brought into close contact. Once forced together, interatomic forces create a bond. Wire or pad contamination, however. hinders this process. To remove organic and inorganic contaminants and form strong, low failure bonds, hybrid components should be plasma cleaned prior to wire bonding. To plasma clean hybrids, plasma of inert gases or a mixture of inert/reactive gases - such as Ar, Ar/Oa, Ar/N2 - chemically removes molecular layers of contamination. Argon mechanically dislodges contaminants, while Ar/02 is a mechanical dislodge and chemical oxidation process. Contaminants can form on hybrids and ICs during assembly. For example, organic contaminants due to poor rinsing after wet chemical photoresist, strip or etch appear on semiconductor die. Hybrids assembled with an epoxy die attach may suffer from resin bleed. When organic resin runs over the adjacent surface of the ceramic and conductors through capillary action, wire bond strength can be reduced. Another contaminant is outgasses produced during epoxy cure. Although modern epoxies are classified as solventless, they contain low molecular weight diluents, which control epoxy viscosity and rheology. By formulation, diluents bind chemically with the epoxy as it polymerizes. Nonetheless, even with an exhaust system in operation, some diluents can be outgassed during epoxy cure and can build up on the hybrid and impede bonding. The dicing process for wafer segmentation is another source of contaminants. Water used to cool the dicing diamond saw blade may have impurities, catalyze contaminants from previous process steps, or result in bond pad corrosion, in addition, the aluminum metallization from which most semiconductor bond pads are made readily oxidizes. If ttiis oxidation layer is too thick, bond pad reliability can suffer. The hybrid assembly environment also inroduces contamination from hand oils used by machine operators, oil fumes and particulates in the air, and more. Containers for hybrid substrates, waffle packs for ICs, and other storage materials can be contamination sources. Careful handling and processing during hybrid and IC assembly can only minimize contamination; therefore, assembly techniques must incorporate a cleaning step in the process flow. Removing epoxy resin bleed is a good method to test plasma cleaning effectiveness - if resin bleed can be eliminated, any nonvisible contaminants present also can be removed. Innitially only Ar gas was used to clean the contamination, but long processing times required were unsuitable for a production environment. A 98% Ar / 2% O2 mixture provided a sufficiently fast process time, although there is always fear that oxygen might discolor the silver filled die attach epoxy. In figure 5a) and 5b) a comparison between AES spectra of an uncleaned and he; '■uyyc't sr^n.Mf, ..aw »ST^ž.ne i« <»» s? uc^si o,r ' ... „ "'-.'»J . i^lägÜ' C. liilii sls&ä SU8StR«TE , CI» P.'N Oi>9<>?fi?SB8jr > BOHD PfiB 2 ___fi^ fscnvesi sijprii!,b. eaa laes isfse UHO isoo tsoe 39 HKCnc EMERSV, ev , ftc; .aoe iiOT=£.e8 te'm sr üs-af v f - —-. Ri^JUBStJiKlgSöäSSrin"®^^ , WNU ptJD ^ ^ÄÄ^IliBBiliilll Hii-. tm ieci 'see lee« tse« iseo iM» KINETIC EHLRCY, FV Figure 5: AES - Scanning Auger microanalysis of a bond pad on a component a) before plasma cleaning b) after plasma cleaning plasma cleaned bond pad (plasma condition: 98%Ar/2%02, 500 W, 15 min, 0.75 torr) demonstrates a sharp reduction in the metallization's carbon peak after plasma clean which also means a reduction in organic contaminant level. Wire bond test results Test results shown in table 4 clearly show the efficacy of plasma cleaning. Samples thermosonically bonded on a semiautomatic gold bonder with 6 to 8 g tensile strength and a 3 to 5 percent elongation wire boasted stronger bonds than did hybrids that had not been plasma cleaned. Bond pull strength increased 13 to 25 % with a 13 to 17 % reduction in the standard deviation. TABLE 4 DESTRUCT PULL TEST SAMPLES SAMPLE 1 Before Cleaning X = 5.3 g After Plasma Cleaning X = 6.65 g S = 1.89 g S = 1.57 g Failure Mechanism Failure Mechanism 8 - Bond lifts 7 - Neck downs 10 - Neck downs 5 - Wire breaks SAMPLE II Before Cleaning After Plasma Cleaning X = 6.78 g X = 6.65 g S = 1.31 g S = 1.57 g Failure Mechanism Failure Mechanism 11 - Bond lifts 23 - Neck downs 1 - Wire break 31 - Neck downs 5 - Wire breaks NON-DESTRUCTIVE WIRE BOND PULL TEST Product 1 Product 2 Uncleaned Plasma Cleaned Total bonds tested - 28.050 ■Total bonds tested -18.305 Total bonds failed - 317 Total bonds failed -12 % Failure 1.13% % Failure 0.066% Plasma Cleaned Total bonds tested -11.826 Total bonds failed -15 % Failure 0.13% A more significant result was a shift in the failure mechanism of the bond when pulled to destruction - failures shifted to neck down and wire breaks versus bond lifts. The cleaner components permitted a reduction in ultrasonic power levels on the bonder and less rework of parts coming off the bonder due to missed bonds. Conclusion Plasma cleaning of hybrids and iCs can increase bond pull forces and reduce standard deviations of destructive pull tests, decrease ultrasonic power levels, and wide the effective bond window. In addition, life tests and non-destructive bond pull tests demonstrate an improvement in long - term reliability. 4.0 APPLICATION OF PLASMA TECHNOLOGY IN PCB PRODUCTION 4.1 PLASMA DESMEARING AND ETCHBACK OF MULTILAYER PRINTED CIRCUIT BOARDS Technics Plasma offers manufacturers of multilayer printed circuit boards a reliable, clean, easy - to - use production tool for removing drill smear from either flex or rigid boards. 110 mg 100 SO Coupon Weight Loss Distribution V/eight loss of spox/ laminate coupons after piasrrra ti^^atment depending on position in process chamber Average voiue \ Position in electrode case Temperature Distribution 110 100 90 80 70 The desree and uniformity ofdesmearing and etch-back can be simulated by measurins tfie weight loss of toe uncovered epoxy laminates. Tf'« sraph shows the variations in the sveight loss in (heindi^duai chambcr locations. These values can be used to estimate the uniformity of etch-back on the inside of the lx>!e. Mean values of 5 test points per circuit boa'd. The temperature is measured with the help of measuring bands. It rises 0.5-1.5'C/min during the process according to the generator power set. Tt>e temperature constantly shown by the process controller is measured by a resistance thermometer. The drill smear found inside drilled holes can be safely removed in an Oxygen - Freon plasma. When desired the system can also be used to perform controlled etch back in multilayer polyimide and epoxy glass boards. The uniformity across one board, from board to board and batch to batch is usurpassed due to patented Planartube electrodes which are driven by low frequency RF generators. Typical performance results are shown in figure 6 where etch rate and laminate temperature uniformity are displayed. As well, in figure 7 typical process sequence is displayed. 1 1 2 3 4 5 6 7 Figure 8: Technics Plasma desmear system Process Chamber Temperature Figure 6: a) etch uniformity versus iaminate position in the chamber b) process temperature versus laminate position in the chamber vccuum setpoint valve gas 1 (O») valve gas 2 (CF.) valve gas 3 (Aux) valve gas 4 (N, for heat cycle only) gas stabilization time iowtemp. set poinf (80°C for example) hi^ temp, set point (IIOX for example) RF-pcwer purge vent timer TVpical sequence .PC-MOO r~L RT 111 ilii I:: Figure 7: Typical process sequence for drill smear removal 4.2 FLUXFREE SOLDERING WITH PLASMA PRETREATMENT Introduction During the wave soldering process the active and passive components are connected with the circuit carrier of the PCB by a collective soldering procedure and thus made an operative flat pack group. The jointning partners are in general supplied in an unsolderable status, covering layers impede the wetting procedures in the solder melting, figure 9. organic layers SnPb CueSns CusSn Cu covering layers impair the soldering Figure 9: Covering layers impair the soldering These layers are organic, they cover as part of industry atmospheres all surfaces and have the even nnore impeding effect the longer the molecule chains of the hydrocarbons are. Further layers are metal oxides originated by reactions with oxygen. Before the solder process can be started a preparation is necessary to ensure the jointing ability. Usually flux is used. Therefore everybody associates wave soldering with flux. A procedure without flux, however, shows differently. The active ingredient in modern, low solid content flux is an organic acid. Heat supply effects the transformation from metal oxide to metal complexes respectively to metal. Due to the unknown supply status of components and PCBs (quality and thickness of the covering layers are usually not known) one has to work with a surplus of flux so that the chemical process may be incomplete and not wanted residues remain on the flat pack groups. These residues may effect the long term reliability by decreasing the surface resistance respectively by migration, in principle these processes apply to all flux variations no matter whether they are conventional colophony formations, low solid content types or formic acid in protective atmosphere solder systems. The solder process is executed under the protective atmosphere wherease the concentration of the remaining oxygen may be higher than in the conventional protective atmosphere systems. The gas consumption runs at 14 - 15 m^/h. The flat pack groups leave the system completely clean and free of any residues. Perspective: Fluxfree reflow soldering under plasma i. Printed circuit board 2. Asssmbiy 3. Plasma pre-trealment 4. Reflow solderir>g under protective atmosphere 1&0 Mm 3oPb (StPAO, OPTIPAD) componant component component Principle of fluxfree soldering SnO, SnOa, PbO form a porous monolith with a very high melting point (1000°C). The surface failure spots are bare after the plasma treatment, since oxygen plasma ashes away all organic contaminants as well as activates the surface increasing its wettability. Now, an appropriate vaporized process material (purified water) is applied to the surface. Condensate precipitates in the fine openings of the oxide layer. When the SnPb layer prepared this way contacts the solder wave the temperature rises fast (500 K/s) and leads to the quick volume expansion of the precipitated condensate amounts. The volume increase (1000 : 1) lifts the oxide layers, fragments are washed away by the moving solder wave and the solder connection is formed by the copper - tin diffusion at the oxide free areas, figure 10. Solder connections generated by such a new method have of course to undergo a line of tests in order to prove their quality and long term reliability. All visual, structural, electrical, physical and burn in tests turned out to be successful. There are no restriction in the range of components that can be processed. All available component shapes are suitable for the plasma method. System Concept A piling device collects pallets (5 off per batch) from the feeder and passes them on to the receptacle drawer of the plasma chamber, figure 11. The chamber closes and evacuates. After completion of the plasma treatment the pallets are extended, separated again, and by means of band conveyor they run into the preheating, used only for tempering. Then the condensation process is effected and the conveyance to the dual wave. a) 1. Initial status 2. Plasma effect oxide ' layK -SnPb 3. Condensation 4. Soldering a) bl35i-D(l Ol oxiöes 6) lluxfiee soWeiKl Hal pack group K zWS b) Figure 10: a) Principle of fluxfree soldering b) Detailed mechanism behind fluxfree soldering C dtnc ar'! u i •>) lif (? t !i > iJ v ;,„{»Ma;(a8..... /plžisma chamber conaensation /2/ R.Buck, ENHANCE HYBRID RELIABILITY THROUGH PLASMA CLEANING, Hybrid Circuit Technology, December 1988 /3/ H.Schmid, Super Fine Cleaning with Liquid Phase Precleaning and Subsequent Plasma Treatment, PC, October 1995 /4/ Technics Plasma GmbH, Application Reports Figure 11: Fluxfree soldering system concept 5.0 LITERATURE /1/ S.Wolf, R.N.Tauber, SILICON PROCESSING FOR THE VLSI ERA, Volumel: Process Technology, Lattice Press 1986, ISBN 0-961672-3-7 For more information about Teclinics Plasma systems and their applications, please call: MIKROIKS d.o.o., Mr. Iztok Šorli Dunajsl