Flexible microdrilling for test electronics

Transcription

1 14 LASER MICROCHACHINING Fexibe microdriing for test eectronics For microdriing diverse hoes in eectronics test rig components, ULTRASHORT PULSE LASERS offer notabe advantages over mechanica driing. A new system approach now makes microdriing and abation possibe even in poymers and ceramics, and with enormous geometric fexibiity. PATRICIA HAMMERS-WEBER AND UDO HEINZEL T he eectronics industry's growing requirements are one major factor driving advances in aser micromachining systems. In particuar, difficut-to-hande materias such as poymers and ceramics need to be processed with higher contour fideity, tightest toerances and high aspect ratios. Pus, the eectronics industry's endess quest for miniaturisation requires ever smaer connectors on semiconductor devices. Accordingy, the rigs used for testing eectronics known as probe cards need to be ever smaer, too (Figure 1). A critica component in these probe cards is the guide pate. It consists of a mechanicay-stabe substrate with thousands of micro-bore hoes, through which the probe card's contact pins must be inserted safey and precisey to ater estabish proper contact with a semiconductor device's connectors. Suitabe substrate materias are hard or soft ceramics. Advanced probe cards demand not ony smaer geometries with tighter toerances, but aso rectanguar hoes which makes mechanica driing no onger sufficienty precise. In contrast, asers deiver repeatabe bore quaity and advanced hoe geometries, accompanied by much shorter process times. USP asers for nonconductors Hard, nonconductive materias can't be processed via EDM (Eectrica Discharge Machining) methods, whereas utrashort puse (USP) asers are particuary we-suited for microdriing. For this, the Puchheim, Germany-based company Scanab MIKROvent, Mainburg Figures: Posaux (1), Scanab (2) Figure 1. A probe card for eectronics testing contains arge numbers of compex microbore hoes

2 L A S E R M I C R O M A C H I N I N G 15 Figure 2. Precsys 5-axis scan system from Scanab suppies a 5-axis scan system caed Precsys (Figure 2). When couped with a femtosecond aser, it processes diverse materias such as metas, poymers or ceramics without considerabe thermay affecting the substrate. Additionay, it machines highy sensitive materias such as nitino, and produces cuts that are burr-free, e.g. for timepiece gears, with edge toerances of ess than 0.3 (Figures 3a and 3b). System design for aser micromachining The Switzerand-based company Posaux deveops systems such as the Femto Mono (Figure 4) for aser micromachining. Here, the company and Busch Microsystems jointy designed xy-stages made of granite to ensure a soid machine structure. Based on this, particuary carefu consideration was given to the aser source, the optica beam path and too-handing kinetics. Additionay, the interpay of > CONTACT MANUFACTURER Scanab GmbH D Puchheim Te info@scanab.de USER Posaux SA CH-2500 Bie Te contact@posaux.com Posaux reies on these basic technoogies: µ-machining and PCB (Printed Circuit Board) for driing, miing, etc. SACE (Spark Assisted Chemica Engraving) EDM (Eectrica Discharge Machining) Femto-Laser

3 16 L A S E R M I C R O M A C H I N I N G D R I L L I N G Figures 3a and 3b. Left: timepiece gear cut from strip materia (Maiechort); right: image section from figure 3a Figure 4. Machine ayout of Femto Mono for aser micromachining the components, incuding cooing, was studied and optimised. The Precsys scan system, equipped with industriay suitabe interfaces, was ikewise integrated by Posaux into its machine, at both the hardware and software eves. An intuitive user interface supports operators in oading the bore image, arranging its parameters and scanning the workpiece surface. Freey definabe hoe geometries faciitate processing and positioning in the µm range. During the machine's deveopment, a critica roe was payed by precise and highy dynamic beam defection for guiding the aser spot on the workpiece. For this, Posaux chose to integrate Scanab's Precsys 5-axis micromachining subsystem, with its robust construction, user-friendy operation and incuded Dricontro software interface. This subsystem aso guides the aser beam in x, y and z machine coordinates with simutaneousy superimposed, adjustabe anges of incidence (positive and negative). And it aows fabrication of micro-cavities with high aspect ratios. In pure 3-axis aser processing of materias, particuary at higher aspect ratios, the conica beam path (caustic) hinders formation of vertica was. In contrast, the Precsys can set the beam on a revoving circuar course during processing, aowing extension of the bore entrance side to form sharp edges and ideay vertica (cyindrica) was. And even negativey conica bore contours are possibe. In addition to circuar shapes, eiptica, rectanguar and ine-shaped geometries can be reiaby fabricated. This scan system was specificay designed for series production. The Precsys is equipped with an automatic fine adjustment feature that stabiises the beam from the aser to the working fied. This is accompished via a sensor in the system that detects positiona and anguar deviations from the idea target beam path and shows this in the Dricontro software. If the aser beam entering the Precsys were to deviate from a user-specified target setpoint, e.g. due to aser-pointer fuc - tuations or therma fuctuations, Figures: Posaux MIKROvent, Mainburg

4 LASER MICROMACHINING 17 Figure 5. SEM (Scanning Eectron Microscope) images of an injector bore hoe, entrance diameter = 90 µm, exit diameter = 105 µm in a 1 mm thick wa then the user coud issue a software command that initiates re-adjustment. This automatic fine adjustment then competes in ess than haf a minute and thus guarantees ong-term process stabiity without eaborate cause anaysis or manua aignment work. The Precsys process observation port acquires rea-time data from the process zone that can be used, for exampe, to monitor processing resuts before proceeding to the next process step. Practicay everyone is driing A simiar machining process can be appied for automotive for the injector hoes, with an entrance diameter of 90 µm and exit diameter of 105 µm in a 1 mm thick wa (diameter-to-depth ratio: 1:10) (Figure 5). Likewise achievabe are diese injector contro passages, with diameters up to 60 µm and a diameter-to-depth ratio of 1:10. When micromachining a probe card or test engineering rig for eectronics, unprecedented demands are paced on scanners. For process Figure 6. Square bore hoes with an edge ength of 40 µm, a 50 µm raster and an Si3N4 substrate 왘

5 18 LASER MICROMACHINING Figure 7. Round bore hoes with a diameter of 40 µm and a 55 µm raster in an S1000 poymer substrate reiabiity within the Precsys subsystem's image fied, round or rectanguar hoes with diameters and edge engths up to 40 µm need to be fabricated whie maintaining a 50 µm raster. Figure 6 depicts processing of a rectanguar bore matrix ( ) in Si3N4 ceramic within the Precsys image fied. The square's edge ength is 40 µm, with a 50 µm raster, resuting in 10 µm thick was. The connecting radii of the four corners were measured at 5 µm. Here, process times of 1.2 s per bore hoe were achieved in a 250 µm thick substrate. Figure 7 shows a bore matrix in an S1000 poymer substrate with a materia thickness of 350 µm. The bore hoes have a diameter of 40 µm, the raster is 55 µm and the process time was 2.5 s per bore hoe. The Swiss Cross in Figure 8 is surrounded by 2,000 square hoes in a poymer (PPS) substrate with a thickness of 350 µm. Each square bore hoe has an edge ength of 40 µm and a wa thickness of 15 µm, resuting in a 55 µm raster. The first 100 square hoes ( matrix) were bored in one operation within the Precsys image fied. Then the stage was repositioned to precisey bore the next 100 hoes. In the exampe, this was performed 20 times over an area of approximatey 7.5 mm². Figure 9 shows a section of the upper eft corner of figure 8. Note the seamess transition between individua matrices. This requires ±1 µm of precision for both workpiece and process positioning, which sums to ±2 µm positioning precision within the machine's working area. As these exampes prove, this highy integrated machine design deivers a controed process with dependabe quaity. Its system-specific caibration aso enabes array processing in an image fied 2.5 mm in diameter, aowing fabrication of consecutive rectanguar bore hoes even beyond the optica axes without the need for workpiece re-positioning. This can noticeaby sash both process times and cost. MI AUTHORS Dr. PATRICIA HAMMERS-WEBER is Program Manager at Scanab GmbH in Puchheim, Germany. UDO HEINZEL is Senior Technoogy Manager at Posaux SA in Bie, Switzerand. Figure 8 (eft). Swiss Cross, surrounded by 2,000 square bore hoes with an edge ength of 40 µm and a 55 µm raster in 350 µm thick PPS Figures: Posaux Figure 9 (right). Section from upper eft corner of figure 8: zoomed view of transition area for six matrices MIKROvent, Mainburg