DE9110287U1 - Device for contactless measurement of core thickness, diameter and concentricity of micro drills in printed circuit board technology - Google Patents

Description

91 6H09DE

Siemens AG

Device for contactless measurement of core thickness, diameter and concentricity of micro drills in printed circuit board technology

To produce through-holes for high-quality circuit boards, so-called micro hard metal drills with nominal diameters of less than 0.4 mm are preferably used. In order to keep the scrap rates of very high-quality and expensive circuit boards, caused by drill breakage and poor quality of the holes, low, very special design requirements are placed on these micro drills. The micro drills are designed in such a way that the core cross-section increases from the drill tip to the drill shaft, while the drill's outer diameter tapers conically towards the drill shaft. In addition, the micro drills must have a very high concentricity.

For the user of such micro drills, it is desirable to have a measuring option in order to record and check compliance with the defined manufacturing tolerances before using the micro drills.

Likewise, it is interesting and necessary for the manufacturers of micro drills to have a non-destructive measuring and testing method to ensure the quality of their products. Due to the high sensitivity to breakage and the very small geometric dimensions of the micro drills, the mechanical measuring probes commonly used for drills with diameters greater than 0.4 mm can no longer be used. For drills with diameters smaller than 0.4 mm, only a destructive sample test could be carried out up to now. In such a sample test, ground samples are produced and then measured using a microscope.

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The invention specified in claim 1 is based on the problem of creating a device for the contactless and thus non-destructive measurement of the core thickness, diameter and concentricity of micro drills.

The advantages achieved with the invention are in particular that a commercially available laser probe intended for surface profile and roughness measurement can be used, the conversion and adaptation of which requires only a small amount of structural effort. In the device according to the invention, a focused laser beam of very low power then scans the surface of the micro drill. This scanning can take place both in the longitudinal direction of the drill's twist part and in the transverse direction to its diameter. This means that an exact topography measurement can be carried out for one longitudinal half of the micro drill. A rotation of the collet by 180* then enables a corresponding topography measurement of the opposite half of the drill. The rotating device is also used to check the concentricity, whereby the laser beam is previously adjusted to the external diameter of the micro drill.

An advantageous embodiment of the invention is specified in claim 2. The further development according to claim 2 requires only the additional use of an X/Y table, a rotary device and a collet when using laser probes with a measuring head that can be moved in the Z direction.

An embodiment of the invention is shown in the drawing and is described in more detail below.

Show it:

Figure 1 shows a device for contactless measurement of the core thickness, diameter and concentricity of micro drills in a highly simplified schematic representation and

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Figure 2 is a diagram created using the device shown in Figure 1, showing the conicity and the core thickness increase of a measured micro drill.

Figure 1 shows a first adjustment device VX that is adjustable in the X direction and a second adjustment device VY that is arranged on top of it and is adjustable in the Y direction. The two adjustment devices VX and VY are adjustable with 1 pm divisions, whereby in the embodiment shown an electrical adjustment is provided using motors MX and MY. The second adjustment device VY carries a rotary device D and a collet Sz. The rotary device D can be swiveled through 360* and is electrically driven. The electrical drive of the rotary device D is not visible in Figure 1, while the corresponding angle of rotation is designated by Dw. The centering axis of the collet Sz and thus also the longitudinal axis of a micro drill Mb clamped in it run in the Z direction.

The focused laser beam Ls of an optical measuring probe, designated as Mt, is aligned perpendicular to the centering axis of the collet Sz, which is not designated in more detail in Figure 1. The probe head Tk of the measuring probe Mt can be adjusted in the Z direction using a second adjustment device VZ. Here too, an electrical adjustment with 1 pm division is provided, with the corresponding motor designated as MZ. ASPC is an evaluation and control PC, whose control line Sl leads to the optical measuring probe Mt.

After clamping a micro drill Mb to be tested in the collet Sz, the focus point of the laser beam Ls is aligned in the X direction with the help of the first adjustment device VX in relation to the micro drill Mb. The focus point can be, for example, in the area of the core diameter or in the

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The laser beam Ls can be placed in the range of the external diameter of the micro drill Mb, although in some cases an intermediate position for recording both areas is also possible. The laser beam Ls is aligned perpendicular to the drill's longitudinal axis or Z axis. By moving the laser beam Ls in the Z direction using the third adjustment device VZ, the micro drill Mb can then be scanned in the longitudinal direction. By evaluating the surface profile of the drill, information is obtained both about the increase in core thickness and about the conicity of the drill's twist part. By scanning in the Y direction and in the Z direction using the adjustment devices VY and VZ, an xopography can be created for one longitudinal half of the micro drill Mb. The topography of the opposite longitudinal half can then be created after rotating the rotating device D by Dw = 180*. If the rotary device D is rotated by Dw = 360* with the drill's longitudinal axis fixed, a cross-sectional profile of the micro drill Mb can be recorded in the corresponding Z plane. By stringing together several Z plane measurements on the evaluation and control PC ASPC, a longitudinal profile of the micro drill Mb can then also be generated.

Figure 2 shows a diagram in which the profile of a micro drill Mb measured in the X direction using the device according to Figure 1 is plotted against the Z direction. In other words, in Figure 2 the measured values of the outside diameter of the drill groove and the core diameter (X direction) are plotted against the longitudinal direction of the drill (Z direction). The diagram contains a statement about the core thickness increase and the conicity of the drill twist part of the micro drill Mb. This statement is illustrated by dot-dash lines KZ and KB, where the dot-dash line KZ shows the core thickness increase, while the dot-dash line KB shows the conicity of the drill. By comparing with specified desired values of the core thickness increase and the conicity

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of a micro drill Mb, the diagram shown in Figure 2 can therefore be used for quality assurance.

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Claims (2)

91 6 H O 9 DE (&ogr; Protection claims 1. Device for contactless measurement of core thickness, diameter and concentricity of micro drills (Mb) in printed circuit board technology, with a collet (Sz) for the centric holding of the micro drill (Mb) to be tested, a rotating device (D) for rotating the collet (Sz) about its centering axis running in the Z direction, - an optical measuring probe (Mt) whose focused laser beam (Ls) is aligned perpendicular to the centering axis of the collet (Sz) and with - three adjustment devices (VX, VY, VZ) with which the probe head (Tk) of the measuring probe (Mt) and the collet chuck (Sz) can be adjusted relative to each other in the X, Y and Z directions, whereby - X ₁ Y and Z are the mutually perpendicular coordinate axes of a spatial Cartesian coordinate system. 2. Device according to claim 1, characterized by a first adjustment device (VX) and a second adjustment device (VY) for adjusting the collet (Sz) in the X direction and in the Y direction and by a third adjustment device (VZ) for adjusting the probe head (Tk) of the measuring probe (Mt) in the Z direction 02 01