TOOL FOR DRILLING/ROUTING OF PRINTED CIRCUIT BOARD MATERIALS

Abstract: A dense cemented carbide product is described. The product is manufactured from WC with a grain size between 0.1 and 0.4 mu m, fine grain size cobalt and ruthenium powders. The product is used in PCB machining operations where the addition of 10-25 % Ru to the binder phase offers up to 25 % wear resistant incrases and up to 100 % increase in chipping resistance in PCB routing compared to conventional materials (6 % cobalt and 0.4 mu m grain size).

Description: Tool for drilling/routing of nte r. i rr.n i t. board The present invention relates to a tool for drill - ing/routing of printed circuit board materials. By alloying the binder phase with Ru in combination with the use of fine grained Co-powder the properties have been improved . Cemented carbide containing Ru as binder phase alone or in combination with the conventional Co and/or Ni is known in the art. For example, AT 268706 discloses a hard metal with Ru, Rh, Pd, Os , Ir, Pt and Re alone or in combination as binder phase. US 4,574,011 discloses a hard metal composition for ornamental purposes with a binder phase of Co, Ni and Ru. GB 1309634 discloses a cutting tool with a Ru binder phase. GB 622041 discloses a hard metal composition a Co+Ru binder phase. The routing of Printed Circuit Board materials requires a wide range of properties from the tool material in order for it to perform successfully. These include a hardness in excess of 2000 HV, a resistance to edge chipping that is best defined by a fracture toughness in excess of 8 MPam 1/2 , a resistance to chemical attack from the resins included in printed circuit boards and a sharp as possible a cutting edge. Some of these requirements conflict, for instance the high hardness tends to mean a reduced edge toughness . The new products for this application can, therefore, require a reduced WC grain size to produce a higher hardness with reduced tough- ness . However, if this is combined with an increase in cobalt content an increased toughness can be achieved for the same hardness . This also results in a sharper cutting edge, which is required. The invention is primarily concerned with the addi- tion of ruthenium to submicron grades of cemented car- bide. The levels of addition vary between 5 and 35, preferably between 15 and 30, wt-% of the binder content with the best results obtained at about 25 wt-%. For best effects the cobalt used should be of the fine grain size cobalt powder having deagglomerated spherical grains of about 0.4 μm average grain size and with a narrow grain size distribution. Preferably the cobalt powder is polyol cobalt. The cobalt contents to which this addition can be made should vary from 5-12%, pref- erably 5-8. The average WC grain size shall be <0.8 μm, preferably <0.4 μm. The cemented carbide of the invention is preferably a straight WC+Co grade but it may also contain <5 wt-% gammaphase. In order to obtain the submicron WC grain size VC+Cr3C2 is added. Because the Ru also acts as a mild grain growth inhibitor an addition of <0.9wt% VC+Cr3C2 is generally satisfactory. Particularly good results are obtained if the VC/Cr3C2 ratio in wt% is 0.2-0.9, preferably 0.4-0.8, most preferably 0.6-0.7. Preferably sin- tering is performed using gas pressure sintering also referred to as sinter-HIP. The invention also relates to the use of a cemented carbide with submicron WC grain size and with a binder phase containing 10-30 wt-% Ru as a tool for drill- ing/routing of printing circuit board materials. The present invention further relates to a method of making a cemented carbide body comprising one or more hard constituents and a binder phase based on cobalt, nickel and/or iron by powder metallurgical methods mil- ling, pressing and sintering of powders forming hard constituents and binder phase whereby said binder phase contains 10-30 wt-% Ru. At least part of the binderphase powder consists of non agglomerated particles of spheroidal morphology of about 0.4 μm average grain size and with a narrow grain size distribution wherein at least 80 % of the particles have sizes in the interval x±O .2x provided that the interval of variation (that is 0.4x) is not smaller than 0.1 μm. The advantages offered by the ruthenium additions are as mentioned a further element of grain growth refinement, an increase in resistance to chemical attack and a strengthening of the binder phase without significantly affecting the edge toughness due to the increase in cobalt content used. Example 1 Cemented carbide PCB-router according to the invention were made with the composition 1.9 % Ru, 5.6 % Cobalt the remainder WC (0.2 μm grain size), with about 0.7 % (VC + Cr3C2) grain growth inhibitor. The material had a hardness of 2080HV and a K1C of 8.75 MPam 1 ^. For comparison the following PCB routers according to prior art were also made. One was 6% cobalt grade with 0.4 μm WC with a hardness of 2000-2100 HV and one with the same hardness but with 5% cobalt and 0.5 μm WC grain size. The routers were ground to 2.4 mm dia and tested as follows : Workmaterial : Copper clad 3 mm thick FR4 PCB, stacked three deep Test 1: 30,000 RPM,1.2 m/min feedrate, 150 m of cut Test 2: 42,000 RPM,2.2 m/min feedrate, 100 m of cut In test 1 routers according to the invention reached 150 m of cut with 25% less average wear than the prior art routers which used 6% cobalt. In test 2 routers according to the invention reached 100 metres of cut with acceptable levels of wear. Routers according to prior art with 5% and 6% cobalt both fractured between 50 and 75 metres. Fxampl e 2 2.4 mm dia routers according to the invention were made from cemented carbides with varying ruthenium contents as follows: Composition 1 1.0%Ru,6.3%Co,0.7VC+Cr 3 C 2 ,0.2 μm WC Composition 2 1.4%Ru,6.0%Co, 0.7VC+Cr 3 C 2 ,0.2 μm WC Composition 3 1.9%Ru,5.6%Co, 0.7VC+Cr 3 C 2 , 0.2 μm WC The routers were tested as follows: Workmaterial : Copper clad 3 mm thick FR4 PCB, stacked three deep Conditions : 30,000 RP , 1.2 m/min feed rate. Machining until fracture. Results: 1.0%Ru variant- 205 m (Average of 4 cutters) 1.4%Ru variant- 333 m (Average of 5 cutters) 1.9%Ru variant- 366 m (Average of 7 cutters) Cemented carbide PCB microdrills according to the invention were made with the composition 2.2 % Ru, 6.4 % Co the remainder WC (0.4 μm grain size), with about 0.8 % (VC + Cr3C2) grain growth inhibitor. The material had a hardness of 2010HV and a K1C of 8 MPam 1 ^. For comparison the following PCB micro drills according to prior art were made using 8% cobalt grade with 0.4 μm WC with a hardness of 1900HV. The microdrills were tested and the wear measured. It was found that the prior art materials exhibited 10- 15 % less wear resistance and 10-15 % less resistance to breakage during an increasing feed rate that started at 15 μm/rev and increasing towards 70.

Claims: Claims 1. Cemented carbide for PCB-drills containing 5-12 % Co binder phase and remainder submicron WC c h a r a c t e r i s e d in that said binder phase fur- ther contains 10-30 wt-% Ru. 2. Cemented carbide according to the preceding claim c h a r a c t e r i s e d in that the binder phase content is 5-8 wt-%. 3. Cemented carbide according to any of the preced- ing claim c h a r a c t e r i s e d in that said binder phase further contains about 25 wt-% Ru. 4. Use of a cemented carbide with submicron WC grain size and with 5-12 % Co binder phase containing 10-30 wt-% Ru as a tool for machining of printed electronic circuit boards and similar composite materials. 5. Method of making a cemented carbide body comprising one or more hard constituents and a binder phase based on cobalt, nickel and/or iron by powder metallurgical methods milling, pressing and sintering of powders forming hard constituents and binder phase whereby said binder phase contains 10-30 wt-% Ru c h a r a c t e r i z e d in that at least part of the binderphase powder consists of non agglomerated particles of spheroidal morphology of about 0.4 μm average grain size and with a narrow grain size distribution wherein at least 80 % of the particles have sizes in the interval x±O .2x provided that the interval of variation (that is 0.4x) is not smaller than 0.1 μm.

Inventors: AUCOTE JOHN, GREARSON ALISTAIR, AUCOTE, JOHN, GREARSON, ALISTAIR
Applicants: AUCOTE JOHN, GREARSON ALISTAIR, SANDVIK AB, AUCOTE, JOHN, GREARSON, ALISTAIR, SANDVIK AB (PUBL)
Application year: 1998
Main classification: C22C29
IPC codes: B23B27, B23B51, C22C1, C22C29