NEW COPPER ELECTROLYTES FOR BLIND MICROVIA FILLING Michael Dietterle, Ph.D. Dr.-Ing. Max Schlötter GmbH & Co. KG Geislingen, Germany dietterle@schloetter.de ABSTRACT Due to progressive miniaturisation in electronics modern handheld devices (e.g. smart phones) integrate an increasing number of functions in one single device. One key element of these devices is the HDI PCB (High Density Interconnect Printed Circuit Board) which enables at minimum space requirement the connection of high pin count IC packages. The interconnection of PCB layers is mainly achieved by blind microvias which typically have diameters less than 150 µm and depths ranging from 50 to 150 µm. In order to achieve a high signal integrity the blind microvias have to be electroplated with copper and therefore appropriate electrolyte systems have been developed. The demand for further miniaturisation and higher reliability necessitated the complete filling of blind microvias with conductive material. Because of several problems related to conductive pastes as filling material the development of electrolytes for the filling of blind microvias with electroplated copper was initiated. After excessive R&D work the first copper electrolytes could be introduced into the market several years ago and they enabled the production of HDI PCBs with stacked blind microvia and via in pad technologies. In order to further increase the number of functions of handheld devices not only filled blind microvias but also finer lines are needed. To save production process steps like chemical or mechanical copper thinning the copper electrolytes must enable a good blind microvia filling but deposit only a minimum thickness of copper onto the PCB surface. After intensive testing new electrolytes have been introduced into the market recently. These systems can be operated with direct current in vertical continuous plating or standard vertical plating lines. The performance of the new electrolyte systems and the reliability of the electroplated copper layers will be presented. Furthermore operating conditions, maintenance and analysis of the electrolytes will be discussed. Key words: copper electroplating, HDI PCB, blind microvia, filling INTRODUCTION Miniaturisation continues to be the defining trend in microelectronics. It is particularly prominent in the field of modern handheld devices (smart phones, mobile phones, digital cameras, camcorders, PDAs, etc.). The indisputable technology driver to date has been the mobile phone: devices have stayed the same size or got smaller, but functionality has been continuously enhanced. The typical example of this is the now-standard combination of mobile phone and digital camera. Growth forecasts are evidence for the rapidly growing popularity of the smart phone, which combines multiple functions - telephony, high-speed internet access, GPS navigation, TV reception, etc. - in a single device. While mobile phone production is forecast to grow by 11.3 % in 2010, a growth of 35.5 % is predicted for smart phones [1]. It is forecast that 506 million smart phones will be produced in 2014, more than double the 2010 figure of 247 million [1]. These estimates show that the trend towards greater miniaturisation continues unabated. However, compact and powerful devices of this kind require extreme miniaturisation, both of IC packages and of PCBs. Increasing integration density of semiconductors is resulting in ever smaller and more powerful IC chips. The number of I/O pins on IC packages has increased in line with the growing number of functions these components perform, to several hundred in some cases [2]. To accommodate such a large number of I/O pins on an IC package, a transition from peripheral array designs to grid array designs was necessary. As IC packages got smaller and functionality expanded, I/O density increased, resulting in reduced I/O pitches. Fanout of numerous closely spaced pins in a grid array configuration took conventional multilayer PCBs to their technical and economic limits, necessitating the development of a new generation of PCBs, the HDI PCBs [3]. As HDI PCBs have a significantly higher interconnect density, they are both more compact and more powerful than conventional multilayer PCBs. If combined with modern IC packages, extremely compact high-performance electronic devices are possible. HDI PCBs The high interconnect density of HDI PCBs is facilitated on the one hand by a low line/space (e.g. 100 µm/100 µm) and on the other by the use of blind microvias to interconnect PCB layers. Blind Microvias In conventional multilayer PCBs, electrical interconnection between individual layers is achieved by through-holes. These require a great deal of space in z-
direction, as a through-hole through the entire PCB is required to connect even two directly adjacent layers. In contrast, electrical interconnection between individual build-up layers in HDI PCBs is achieved by blind microvias. These require significantly less space than through-holes, as they allow two adjacent layers to be connected without engrossing the areas above and below the connection itself (Figure 1). Therefore these areas can instead be used for conductor paths or blind microvias between further layers, resulting in a significantly higher interconnect density than in conventional multilayer PCBs. Figure 1 shows the schematic structure of a 2-4-2 HDI PCB. The PCB consists of a 4-layer multilayer core with two build-up layers on either side. Figure 1. Schematic structure of a HDI PCB In accordance with IPC/JPCA-2315, blind microvias have a maximum diameter of 150 µm and are today predominantly implemented using laser drilling. Whereas a typical blind microvia has a diameter in the region of 50 to 150 µm, the diameter of a through-hole is usually at least 200 µm. Thus blind microvias require less space than through-holes in x- and y-directions too. Through-holes are used as little as possible in HDI PCBs, and in some cases are completely absent. This further increases interconnect density. In the early years of HDI technology, rather than being filled with copper, blind microvias were simply copperplated [4]. As the deposits produced by existing processes were not satisfactory, new copper electrolytes specifically for this purpose needed to be developed. In combination with suitable pretreatment processes, these produce a reliable conformally electroplated copper layer inside the blind microvias (Figure 2). The compact nature of blind microvias also means that they permit greater signal integrity than through-holes. Signal loss between layers is therefore reduced, which is particularly important in high-frequency applications. Blind Microvia Filling Continued increases in IC integration density led to a further reduction in the I/O pitches of IC packages, resulting in further increases in PCB interconnect density. This was made possible by complete filling of blind microvias with electroplated copper [4]. Compared with unfilled blind microvias, copper-filled blind microvias offer the following advantages: enable stacked blind microvias enable via-in-pad designs improved reliability improved thermal management Stacked blind microvias are blind microvias positioned directly on top of one another (Figure 3). This arrangement allows the use of blind microvias to create conductive connections between non-adjacent build-up layers while using minimal space, which increases interconnect density still further. By using all-stacked blind microvia structures, the use of through-holes can be avoided entirely (Figure 3b). Figure 3. Stacked blind microvias, a) 3 stacked blind microvias, b) all stacked blind microvias In outer layers, copper-filled blind microvias also allow the use of space-saving via-in-pad structures (Figure 4). In these structures, blind microvias function as both via and pad. This further increases interconnect density, as the use of dog-bone (pad-trace-via) designs can be avoided. Figure 4. Via in pad Figure 2. Blind microvia, conformally copper-plated The filling of blind microvias with electroplated copper improves the PCB reliability because the filling consists of only one material. If blind microvias are filled with other materials (e.g. conductive pastes) than electroplated copper, two materials are present inside the blind
microvia: conformally plated copper + filling material. This leads to an additional phase boundary and two different CTEs (Coefficient of Thermal Expansion). These can negatively affect the PCB reliability. Filling with copper also improves the thermal management of the PCB because of the high thermal conductivity of this metal. Production of HDI PCBs Manufacture of HDI PCB requires new manufacturing technologies, such as the SBU (Sequential Build-Up) technique. Figure 5 depicts a typical production sequence for HDI PCBs with copper-filled blind microvias (not all process steps are shown). Figure 5. HDI PCB production, SBU process, panel plate blind microvia filling, tent & etch A dielectric with copper, e.g. RCC (resin-coated copper) foil or an LDPP (laser-drillable prepreg), is first applied to a core. Blind microvias are then laser-drilled and carefully cleaned to remove drilling residues. Electroless copper or direct metallisation may be used for the conductive layer, and this may be followed by pre-reinforcement with electroplated copper (copper strike). After cleaning and activation, the blind microvias are filled by copper electroplating using special copper electrolytes (process step 5). Depending on line/space requirements and copper layer thickness, the copper layer on the PCB surface must be thinned by CMP (Chemical Mechanical Polishing) prior to etching the conductive pattern. Following application and structuring of the photoresist, the conductive pattern is etched. Photoresist stripping is the final step. If another build-up layer is required, the process is repeated from step 2. Established and New Blind Microvia Filling Requirements Blind microvias must be filled void-free, as electrolyte inclusions may lead to PCB reliability issues. In most cases, a minimum filling requirement is specified based on the diameter and depth of the blind microvia (Figure 6a). The filling is often defined in terms of the dent or dimple - the divergence of the filling actually achieved from the ideal planar (dent = 0 µm) surface (Figure 6b). Typical specifications may be for example dent < 25 µm or dent < 10 µm. Figure 6. Blind microvia, a) diameter and depth, b) dent and copper thickness of filled blind microvia Today, continued miniaturisation requires conductive patterns with line/space 75 µm/75 µm and lower. In order to etch such a fine conductive pattern of the panel plated copper without excessive underetching, the total copper thickness (Figure 6b) before etching must be correspondingly low. While copper thickness can be reduced by performing one or more copper thinning cycles, as shown in Figure 5, this increases costs and reduces productivity. Productivity can be increased and costs reduced by omitting the copper thinning step totally, or at least reducing the number of copper thinning cycles required. To permit this, the total thickness of the copper layer (Cu laminate + Cu strike layer, if present + Cu blind microvia filling) on the PCB must be reduced. A number of PCB manufacturers therefore specify a maximum copper layer thickness of 25 µm. This means that only approximately 18 µm of copper may be deposited on the PCB surface during the blind microvia filling process step. Besides the advantages in terms of productivity and costs this also implies less waste of material because less Cu has to be plated and etched subsequently. ESTABLISHED ELECTROLYTES FOR BLIND MICROVIA FILLING Processes for blind microvia filling by copper electroplating have been used on a large scale for a number of years, principally by Asian PCB manufacturers. To achieve the required coating properties, these processes use high-levelling sulphuric acid copper electrolytes containing organic bath additives alongside copper sulphate, sulphuric acid and chloride. Several types of blind microvia filling electrolytes are now commercially available from a number of suppliers. The various processes differ in the following main areas: Organic additive system Anode material (copper anodes or insoluble anodes) Applied current form (DC (Direct Current) or RPP (Reverse Pulse Plating)) Type of plating line used (standard vertical, vertical continuous or horizontal continuous) Applicable current density The copper electrolytes discussed below were all developed by the company where the author is employed.
A typical filling result achieved with the predecessor of the new electrolyte, which has been commercially available for around five years, is shown in Figure 7. The micrograph shows a fully copper-filled blind microvia (ø: 100 µm/depth: 65 µm) after electroplating at 1.5 A/dm 2 over 68 minutes. Dent is 10.1 µm and plated copper thickness is 22.7 µm. Figure 7. Blind microvia (Ø: 100 µm, depth: 65 µm) filling Cu thickness: 22.7 µm, dent: 10.1 µm 1.5 A/dm 2 / 68 min. NEW ELECTROLYTES FOR BLIND MICROVIA FILLING Although the filling shown in Figure 7 is very good, the copper thickness of 22.7 µm exceeds the limit of 18 µm required for line/space 75 µm/75 µm. In order to meet this limit, new electrolytes offering improved filling performance needed to be developed. The objective is to deposit less copper onto the surface of the PCB than previously while achieving at least as good filling. This is often referred to as superfilling. In addition, plating times must not be longer than in established processes, and continued use of present plating equipment should be possible. Intensive R&D work and numerous tests resulted in the development of a new electrolyte for blind microvia filling providing better filling performance and thus a reduced copper thickness on the surface. Figure 8 shows the filling achieved with this new electrolyte in a blind microvia with the same dimensions as that in Figure 7. Copper thickness was reduced from 22.7 µm to 10.7 µm for a plating time of 60 minutes and a current density of 1.5 A/dm 2. The dent is 7.6 µm. Figure 8. Blind microvia (Ø: 100 µm, depth: 65 µm) filling Cu thickness: 10.7 µm, dent: 7.6 µm 1.5 A/dm 2 / 60 min. As can be seen in a comparison of Figure 7 and Figure 8, the new electrolyte permits copper thickness to be significantly reduced while also achieving a slightly better filling (the dent is shallower). The plating time was shortened by 8 minutes. In addition, the new electrolyte can be used in the same plating plant as its predecessor and does not require any alterations to equipment. Filling of Blind Microvias, Requirement: dent < 10 µm, copper thickness < 18 µm The performance of the new electrolyte will first be demonstrated for the requirements dent < 10 µm and copper thickness < 18 µm. PCBs (size: 500 mm x 400 mm) with blind microvias (Ø: 100 µm, depth: 80 µm) were copper-plated in a 1400-litre test module equipped with insoluble anodes. This test module is identical in construction to the electroplating module of a vertical continuous plating line introduced into market a few years ago. Unless otherwise stated, all tests were carried out using PCBs which were treated with electroless copper. Figure 9 shows the filling achieved after plating for 75 minutes at 1.2 A/dm 2. The blind microvia is completely filled with copper, the copper thickness is 15.8 µm and the dent is 0 µm: Figure 9. Blind microvia (Ø: 100 µm, depth: 80 µm) filling Cu thickness: 15.8 µm, dent: 0 µm 1.2 A/dm 2 / 75 min. The filling achieved with these parameters is excellent, but at a current density of 1.2 A/dm 2, productivity is insufficient. Completion of blind microvia filling within a maximum of 70 minutes was therefore requested. In the subsequent test, plating time was reduced from 75 to 60 minutes and current density increased from 1.2 to 1.5 A/dm 2, so the same amount of electric charge was available for copper-plating in both tests. Figure 10 shows that complete blind microvia filling was achieved even with a shorter plating time of 60 minutes. The dent increased from 0 µm to 9.5 µm, while the copper thickness remained practically unchanged. This result shows that the new process is able to fulfill the requirements regarding dent and copper thickness outlined above.
22.3 µm is achieved with a current density of 2.0 A/dm 2 and a 55-minute plating time (Figure 12a). Increasing the current density further to 2.5 A/dm 2 produces a dent of 20.9 µm and a copper thickness of 23.3 µm over a plating time of only 45 minutes (Figure 12b). Figure 10. Blind microvia (Ø: 100 µm, depth: 80 µm) filling Cu thickness: 15.2 µm, dent: 9.5 µm 1.5 A/dm 2 / 60 min. Blind microvia filling can be further improved by electroplating of a thin copper strike after electroless copper-plating. Figure 11 shows the filling result achieved when a copper strike was applied. With a copper strike, the dent is reduced from 9.5 µm to 6.3 µm. Figure 11. Blind microvia (Ø: 100 µm, depth: 80 µm) filling Cu thickness: 14.8 µm, dent: 6.3 µm 1.5 A/dm 2 / 60 min. (blind microvia filling) The pre-reinforcement of the conductive layer (electroless copper or direct metallisation) with an electroplated copper strike is an ideal base layer for subsequent filling. A thin copper layer with a thickness of only 2-5 µm is sufficient. Appropriate pre-treatment (e.g. acid cleaner) produces an active copper surface that facilitates a very quick onset of the blind microvia filling. With all other parameters unchanged, this results in an improved filling. Application of a copper strike frequently permits blind microvia filling to be carried out at higher current densities leading to shorter plating times. In the tests described herein, the copper strike was produced using an electrolyte which is utilized for copper-plating of blind microvias in large scale PCB production. Filling of Blind Microvias, Requirement: dent < 25 µm, copper thickness < 25 µm If lower requirements for blind microvia filling (e.g. dent < 25 µm) and copper thickness (e.g. copper thickness < 25 µm) are possible, very good results can be achieved with the new electrolyte even with short plating times and high current densities. For blind microvias (Ø: 100 µm, depth: 80 µm) a dent of 13.3 µm and a copper thickness of Figure 12. Blind microvia (Ø: 100 µm, depth: 80 µm) filling: a) Cu thickness: 22.3 µm, dent: 13.3 µm 2.0 A/dm 2 / 55 min. b) Cu thickness: 23.3 µm, dent: 20.9 µm 2.5 A/dm 2 / 45 min. The new electrolyte can also produce a good filling in large size blind microvias. These have a larger volume, meaning that more copper is required for filling and the plating time for a current density of 1.5 A/dm 2 needed to be prolonged to 90 minutes. For a blind microvia (Ø: 100 µm, depth: 100 µm), a dent of 4.4 µm and a copper thickness of 24.6 µm was achieved (Figure 13a). For a significantly larger blind microvia (Ø: 150 µm, depth: 100 µm), a dent of 20.2 µm and a copper thickness of 23.7 µm could be achieved (Figure 13b) using the plating parameters as mentioned above. Figure 13. a) Blind microvia (Ø: 100 µm, depth: 100 µm) filling: Cu thickness: 24.6 µm, dent: 4.4 µm 1.5 A/dm 2 / 90 min. b) Blind microvia (Ø: 150 µm, depth: 100 µm) filling Cu thickness: 23.7 µm, dent: 20.2 µm 1.5 A/dm 2 / 90 min. Blind Microvia Filling in Conjunction with Direct Metallisation The new blind microvia filling electrolyte can also be used for PCBs that have been treated with direct metallisation. Figure 14 shows the filling achieved on a PCB treated using a graphite-based direct metallisation process. However, with unchanged plating parameters, a slightly
worse filling was achieved compared to the PCB which was treated with electroless copper (Figure 10). Figure 16. Blind microvia filling and pattern plating 1.2 A/dm 2 / 68 min. Figure 14. Blind microvia (Ø: 100 µm, depth: 80 µm, direct metallisation) filling: Cu thickness: 16.4 µm, dent: 17.1 µm 1.5 A/dm 2 / 60 min. Deposition of a copper strike improves blind microvia filling considerably, even on PCBs treated with direct metallisation. Figure 15a shows a blind microvia (Ø: 110 µm, depth: 60 µm) in a PCB treated with graphite-based direct metallisation after deposition of a copper strike. It is clearly apparent that the copper strike was not deposited conformally and that the copper thickness is greater in the area of the capture pad/dielectric transition. In combination with the active surface of the copper strike, this geometry provides ideal conditions for subsequent blind microvia filling and permits a higher current density and shorter plating time to be used. Figure 15b shows very good blind microvia filling after deposition at 1.9 A/dm 2 over 50 minutes. Figure 15. Blind microvia (Ø: 110 µm, depth: 60 µm, direct metallisation) filling: a) after copper strike b) after blind microvia filling (1.9 A/dm 2 / 50 min.) Cu thickness: 16.4 µm, dent: 1.9 µm Blind Microvia Filling and Pattern Plating As depicted in Figure 16 the new electrolyte for blind microvia filling can also be used for pattern plating, but little experimental data is currently available. Blind microvia Filling and Through-hole Plating The new electrolyte for blind microvia filling can also be used for plating of through-holes (Figure 17). However, it should be noted that good throwing power between 70 and 100 % can only be achieved with thin PCBs and low aspect ratios. As with pattern plating, little experimental data is currently available for through-hole plating. Figure 17. Through hole plating Through hole diameter: 250 µm, board thickness: 1 mm Throwing power: 90 % 1.2 A/dm 2 / 68 min. Blind Microvia Shape and Filling Result Alongside electrolyte and plating parameters, the blind microvia filling result is also strongly dependent on the size and shape of the unfilled blind microvias. The best filling results are achieved with conical blind microvia shapes. However, blind microvia shapes encountered in practice often deviate significantly from this ideal. Depending on the dielectric type and the laser drilling parameters, significant overhangs respectively recessions can result (see circles in Figure 18a and b). Figure 18. Blind microvias with overhangs/recessions a) after laser drilling; b) after copper strike Overhangs and recessions impede electrolyte exchange and negatively affect the electric field, so filling gets considerably more difficult. To achieve a good filling result in such cases, it is often necessary to deposit a copper strike prior to blind microvia filling (Figure 18b).
The new electrolyte for blind microvia filling also allows overhangs and recessions to be filled with copper without defects (see circles in Figure 19). A copper strike was used in this case. Figure 19. Blind microvia with overhangs/recessions Blind microvia (Ø: 120 µm, depth: 60 µm) filling: Cu thickness: 16.4 µm, dent: 8.2 µm 1.5 A/dm 2 / 68 min. Reliability The reliability of electroplated copper layers is an important quality criterion in PCB production, and appropriate reliability tests must be performed on an ongoing basis. The copper layers deposited using the new electrolyte for blind microvia filling exhibit an elongation of about 20 % and pass the reliability tests given in Table 1. Thermal Stress Thermal Shock 288 o C (10 s), 5 times no crack, no delamination LLTS no crack, (-65 o C, 5 min. // +125 o C, 5 min.) no delamination 300 cycles IR Reflow (200-240 - 260-280 o C, 0.5 m/min.), 8 cycles Table 1. Reliability test results resistance change < 5 % Electrolyte Makeup and Maintenance The electrolyte is made up with copper sulphate, sulphuric acid and hydrochloric acid, and contains three organic bath additives alongside the inorganic ingredients. The concentration ranges of each of the electrolyte components are given in Table 2. To ensure a good blind microvia filling it is quite common that the copper ion concentration in blind microvia filling electrolytes is significantly higher in comparison to other copper electrolytes for PCB production. Cu 2+ 40-60 g/l Sulphuric acid, conc. 20-90 g/l Chloride 50-70 mg/l Suppressor 5-10 ml/l Grain refiner 0.1-0.5 ml/l Leveller 0.2-2.0 ml/l Table 2. Concentration ranges of electrolyte components The methods used for analysis of the individual electrolyte components are summarized in Table 3. The leveller content of the electrolyte can be evaluated by plating a Hull cell panel. A CPVS (Cyclic Pulse Voltammetric Stripping) method for leveller analysis is currently under investigation. iodometric titration Sulphuric acid alkalimetric titration Chloride potentiometric titration HPTLC (High Performance Thin Suppressor Layer Chromatography) CVS (Cyclic Voltammetric Grain refiner Stripping) Hull cell Leveller CPVS (Cyclic Pulse Voltammetric Stripping) under investigation Table 3. Analysis of electrolyte components Cu 2+ Operating Conditions The main operating conditions for the new electrolyte are shown in Table 4. The electrolyte is used under direct current conditions and with insoluble anodes at a maximum temperature of 22 C. Replenishment of copper ions is performed by dissolution of copper oxide in a separate dissolving unit and subsequent addition to the plating tank. It is preferable to operate the electrolyte in a VCP (Vertical Continuous Plating) line. This equipment combines the advantages of horizontal continuous plating lines with those of standard vertical plating lines. VCP lines have come into widespread use by Asian PCB manufacturers over recent years. The electrolyte may also be used in standard vertical plating equipment, but VCP lines generally produce somewhat better results. Anode Insoluble (Mixed Metal Oxide) Current Direct Current Current density 1-2.5 A/dm 2 Temperature 18-22 C Copper (makeup) CuSO 4 5H 2 O Copper (replenishment) CuO (< 0.05 % Cl - ) Vertical continuous plating line Plating plant (recommended) Standard vertical plating line (possible) Table 4. Operating conditions Mass Production Experience The new electrolyte for blind microvia filling has been used in a VCP line in mass production of PCBs (line/space 75 µm/75 µm respectively 60 µm/60 µm) for about six months. Filling of blind microvias (Ø: 110 µm, depth: 60 µm) is carried out at a current density of 1.5 A/dm 2 over a plating time of 52 minutes. The dent is less than 10 µm. The resultant copper thickness is approximately 15 µm, and this can be reduced to the final thickness required for the subsequent tent and etch process by a single copper thinning cycle.
Before the new electrolyte was available, its predecessor was operated in the same plant. Using this previous electrolyte, complete blind microvia filling was achieved with the same current density of 1.5 A/dm 2 but a plating time of 68 minutes. However, the copper thickness achieved was approximately 20 µm, requiring the copper thinning process to be repeated multiple times. Thus the new electrolyte allows both the blind microvia filling process and copper thinning process to be carried out more quickly. This leads to cost reduction, increasing productivity and less waste of copper. SUMMARY The superior filling performance of the new electrolyte permits blind microvias (Ø: 100 µm, depth: 80 µm) to be completely filled with electroplated copper (dent < 10 µm) while producing a lower copper thickness (< 18 µm) on the PCB surface. This enables blind microvia filling and line/space 75 µm/75 µm respectively 60 µm/60 µm via tent & etch process without requiring multiple copper thinning cycles. This increases productivity, reduces costs and leads to less waste of copper. [2] J.W. Stafford, Semiconductor Packaging Technology, Printed Circuits Handbook, 5 th edition, ed. by C.F. Coombs, McCraw-Hill, 2001, pp. 2.1-2.22. [3] C.F. Coombs and H.T. Holden, Electronic Packaging and High-Density Interconnectivity, Printed Circuits Handbook, 5 th edition, ed. by C.F. Coombs, McCraw-Hill, 2001, pp. 1.3-1.22. [4] M. Carano, Electrodeposition and Solderable Finishes for HDI, The HDI Handbook, 1 st edition, ed. by H. Holden, BR Publishing Inc., 2009, pp. 355-397. [5] H. Holden, The HDI Manufacturing Processes, The HDI Handbook, 1 st edition, ed. by H. Holden, BR Publishing Inc., 2009, pp. 231-257. In case of lower dent and copper thickness requirements, blind microvias (Ø: 100 µm, depth: 80 µm) can be completely filled with copper over even very short plating times. Even very large blind microvias (Ø: 150 µm, depth: 100 µm) can be completely filled with copper over reasonable plating times. The new process can also be used in the production of HDI PCBs treated with graphite-based direct metallisation processes. A copper strike can be applied to increase the filling further, both with direct metallisation and with electroless copper. The electroplated copper layers meet the common reliability test requirements for PCBs. Experience with the electrolyte in mass production of HDI PCBs to date shows that the new electrolyte permits stable and reliable blind microvia filling. The electrolyte can also be used for pattern plating and through-hole plating, but only a small amount of experimental data is currently available on this. ACKNOWLEDGEMENT The author would like to acknowledge the support of AGES Group (Taiwan), and particularly Mr. Albert Yeh, in this project. REFERENCES [1] T. Teng, isupply Issues Fast Facts on Latest iphones, isupply, press release June 7, 2010.