Method for applying a metallization to a plurality of electronic components

The present invention concerns a method for applying a metallization to a plurality of electronic components. In particular, the metallization is applied to surface-mounted devices components (SMD components).

To apply a metallization to SMD components, the components are arranged in a carrier and dipped into a metallization paste. Deviation of the distance of the component from one component to the other versus a reference dipping plane on which a dipping process is performed leads to deviations of crucial parameters of the metallization such as thickness and geometrical tolerances. Therefore, it is crucial to arrange the electronic components in the carrier versus the reference dipping plane very precise before dipping.

It is the object of the present invention to propose an improved method for applying a metallization. For example, the method shall be designed to minimize deviations in the distance of the components against the reference dipping plane.

This object is solved by a method according to claim 1.

A method for applying a metallization to a plurality of electronic components is proposed which comprises the following steps: a. Providing a carrier having a first surface and a second surface opposite the first surface, wherein the carrier comprises holes which extend from the first surface to the second surface, b. Pressing each electronic component at the first surface into one of the holes such that the electronic component protrudes from the carrier at the second surface, c. Pushing each of the electronic components into the carrier towards the first surface such that the distance by which the electronic components protrude from the second surface is reduced, d. Dipping the electronic components protruding from the second surface of the carrier into a paste.

Accordingly, the electronic components are arranged in the carrier before the dipping in a two-step pressing process. In step b., each electronic component is pressed in a direction from the first surface to the second surface of the carrier and, afterwards, in step c., the electronic components are pressed or pushed in the opposite direction. In step c., the electronic components can be pressed against a flat plate which pushes the electronic components towards the first surface. The flat plate is further on referred as reference dipping plane. Accordingly, the electronic components can be levelled against the reference dipping plane.

Then the metallization paste can be applied over the reference dipping plane by an appropriate method in even thickness and the dipping step can be performed. By levelling against the reference dipping plane the position of the electronic components in the carrier can be set very precisely against the reference dipping plane. In this way it can be ensured that each electronic component is dipped into the paste by the same distance such that the paste is applied over the same length and with the same thickness on each component.

The electronic component can be any electronic component. For example, the electronic component can be an SMD component (SMD = surface mounted device).

The carrier can be a flat carrier. The carrier can have a thickness which is smaller than its width and its length. The thickness is the distance from the first surface to the second surface of the carrier. The thickness of the carrier can be smaller than a length of the electronic components.

The holes may protrude through the carrier. An electronic component that is pressed into the hole at the first surface can accordingly travel through the carrier and can protrude from the second surface of the carrier.

In step b. the electronic components are pressed into the carrier such that they protrude from the carrier at the second surface. The electronic components can be pressed into the carrier such that at least a part of the electronic components remains in the carrier at the end of step b.

In step c. the electronic components may be pushed into the carrier towards the first surface by a defined distance. The electronic components may be pushed towards the first surface by such a distance that the electronic components protrude from the first surface and from the second surface. Electronic components can be pushed by movement onto the reference dipping plane, thus levelling themselves according to the geometry of reference dipping plane.

In step d. the paste can be first applied in even thickness across the reference dipping plane and the metallization is then applied by dipping the electronic components into the paste. The paste may be a metallic paste which forms the metallization after drying.

In step b. the carrier may first be mounted to a container or a metal holder. Using a container which fixes the carrier may further improve the precision of the method. In particular, the container may have a thickness tolerance lower than 10 pm.

In step c. the carrier may be mounted on a dipping head such that the first surface of the carrier faces the dipping head and, in step c., the dipping head holding the carrier may be moved against the reference dipping plane. A dipping head may be a machine configured to hold the carrier, to move the carrier and to dip the carrier into the paste.

In step c., the carrier may be moved towards the reference dipping plane, wherein the second surface of the carrier faces the reference dipping plane, such that the electronic components abut the reference dipping plane and the electronic components are pushed into the carrier towards the first surface by movement against reference dipping plane and the distance by which the electronic components protrude from the second surface is reduced. After step c. and prior to step d., the paste can be applied to the reference dipping plane in even thickness, and in step d., the electronic components are dipped into the paste applied on the reference dipping plane. As the reference dipping plane can be used for pushing the components towards the first surface of the carrier in step c. and as the dipping plane in step d., any geometric irregularity in the reference dipping plane will effect the levelling in step c. and also the dipping in step d. such that the geometric irregularity has only a minimal effect on the applied metallization. The levelling is done with reference to the actual plane on which the dipping is done.

In a preferred embodiment, the holes have a non-round layout. For example, the holes may have a rectangular cross-section in a plane parallel to the first surface of the carrier. The electronic components may also have a rectangular layout. In contrast to holes having a round layout, the rotation of electronic components inside a hole which has a rectangular layout is minimized and, thereby, angling of the electronic components relative to a longitudinal axis of the hole is minimized. Providing the hole with a rectangular layout reduces the tolerance of the metallization.

The carrier may comprise a first layer of a soft material, e.g. silicon, at the first surface and a second layer of the soft material, e.g. silicon, at the second surface. A metal layer may be arranged between the first layer of the soft material and the second layer of the soft material. The layers of the soft material may ensure that electronic components are held in carrier during dipping process without movement. Further, the silicon layer may prevent that the electronic components are damaged by scratches from the metal layer. The layers of the soft material can comprise holes having dimensions smaller than the dimensions of the electronic components.

Prior to step b. the electronic components may be held in slots of a container. In step b., the carrier may be arranged on top of the container such that the holes are aligned with the electronic components and the slots.

The container may have a thickness tolerance lower than 10 pm.

In step b. the electronic components may be pressed into the carrier by a tool, for example by a metal needle or by metal needles. Using a tool to press the electronic components from the container into the carrier allows to position the components in the carrier, and, further ensures that the electronic components are moved purely linear such that they are not arranged at an oblique angle inside the holes of the carrier .

After step b. is completed, the electronic components may protrude from the second surface of the carrier, wherein the electronic components protrude from the second surface by a distance that is larger than the distance by which the electronic components protrude from the first surface. After step c. is completed, the electronic components are levelled against the reference dipping plane with lowest possible difference of relative distance of each component versus the reference dipping plane.

After step d. the electronic components protruding from the first surface of the carrier are dipped into the paste. In particular, the paste may be dried and afterwards the carrier may be inverted and again fixed to the dipping head.

In the following, preferred embodiments of the invention are described with reference to the figures.

Figure 1 shows a process diagram for a method for applying a metallization to a plurality of electronic components.

Figure 2 shows a top view of a carrier.

Figure 3 and Figure 4 show a first pressing step of the method, wherein electronic components are pressed into the carrier .

Figure 5 shows the carrier being mounted to a dipping head.

Figure 6 shows a second pressing step of the method, wherein electronic components are pressed into the opposite direction against the reference dipping plane.

Figure 7 schematically shows an electronic component after the method has been completed.

Figure 1 shows a process diagram for a method for applying a metallization 2a, 2b to a plurality of electronic components 1. The electronic components 1 can be, for example, surface- mounted devices (SMD). The metallization 2a, 2b is applied to form a metallization for the electronic component 1.

The electronic components 1 can be ashlar-formed. Accordingly, the electronic components 1 can have a rectangular or quadratic layout. Each electronic component 1 comprises a first end la and a second end lb which is opposite of the first end la. During the method, a first metallization 2a covering the first end la and a second metallization 2b covering the second end lb are applied to the electronic components 1.

In a first step a. of the method, a plurality of electronic components 1 and a carrier 3 are provided. At this stage of the method, the electronic components 1 do not comprise the metallizations 2a, 2b covering the ends la, lb of the electronic components 1.

Figure 2 shows a top view of the carrier 3. The carrier 3 is flat. The carrier 3 comprises a metal layer 11 and a first layer 12 of a soft material which covers a first surface 3a of the carrier 3. Additionally, the carrier 3 comprises a second layer 13 of the soft material covering the second surface 3b of the carrier 3 which is opposite of the first surface 3a. Accordingly, the metal layer 11 is sandwiched by the first layer 12 of the soft material and the second layer 13 of the soft material. The soft material can be silicon.

The electronic components 1 have a length which is longer than the thickness of the carrier 3. The length of the electronic components 1 is defined as the distance from the respective first end la to the respective second end lb. The thickness of the carrier 3 is defined as the distance from a first surface 3a of the carrier 3 to a second surface 3b of the carrier 3. As the length of the electronic components 1 is longer than the thickness of the carrier 3, the electronic components 1 can simultaneously protrude from the first surface 3a and from the second surface 3b of the carrier 3. The carrier 3 comprises holes 4 which are configured to receive the electronic components 1. The holes 4 extend from the first surface 3a of the carrier 3 to the second surface 3b of the carrier 3. Accordingly, the holes 4 protrude through the carrier 4. The holes 4 protrude through the first layer 12 of the soft material, the metal layer 11 and the second layer 13 of the soft material.

As shown in Figure 3, the carrier 3 is arranged on a container 6. The container 6 comprises slots 7. The electronic components 1 are arranged in the slots 7.

The slots 7 in container 6 have a rectangular layout. The layout of the slots 7 is adapted to the shape of electronic components 1. The layout of the slots 7 is slightly bigger then layout of the electronic components 1 to allow a movement of the electronic components 1 in the slots 7. In the metal layer 11 of carrier 3, the holes 4 may or may not have a rectangular layout. The layout of the holes 4 is slightly bigger than the layout of the electronic components 1.

The electronic components 1 are held in the carrier 3 by the holes 4 in the layers 12, 13 of the soft material. The holes 4 in the layers 12, 13 of the soft material are rectangular. The layout of the holes 4 in the layers 12, 13 of the soft material is adapt to shape of the electronic component 1. The layout of the holes 4 in the layers 12, 13 of the soft material is smaller than layout of the electronic components 1, thus the layers 12, 13 of the soft material firmly hold the electronic component 1 during the dipping process in the carrier. When holding the electronic components 1, the soft material is deformed elastically by the electronic components

1.

By providing holes 4 in the layers 12, 13 of the soft material in the carrier 3 which are not rotationally symmetric, it is ensured that an electronic component 1 being arranged in one of the holes 4 neither angles relative to a vertical axis 5 of the hole 4 nor rotates in the hole 4. The vertical axis 5 is perpendicular to the first surface 3a of the carrier 3. As neither a rotation nor a shift in the angle of the electronic component 1 to the vertical axis 5 is possible, it is ensured that an orientation of the electronic component 1 relative to the vertical axis 5 of the hole 4 cannot be altered after the electronic component 1 is received in the hole 4. Once the electronic component 1 is inserted into the hole 4, the electronic component 1 can only be moved linearly along the vertical axis 5 of the hole 4. This allows to position the electronic component 1 with a high precision in the carrier 3.

Each electronic component 1 abuts the layers 12, 13 of the soft material above and below a middle of a corresponding hole. The coefficient of friction between the soft material and the electronic component 1 determines which force has to be applied to move the electronic component 1 linearly along the vertical axis 5.

Each of Figures 3 to 6 shows a stage of the method of inserting electronic components 1 into the carrier 3 and proper levelling of the electronic components 1 in the carrier 3 prior to the dipping process. In each of Figures 3 to 6, the area on which the paste is applied in the dipping steps in marked as area laa, lbb. At the stages of the methods shown in Figures 1 to 6, the paste which forms the metallization is not yet applied. The area laa, 2aa is marked only to improve the visualization.

In step b. of the method, the electronic components 1 are pressed into the holes 4 of the carrier 3 from the first surface 3a of the carrier 3 such that the electronic components 1 protrude from the second surface 3b of the carrier 3. Figure 3 and Figure 4 show step b. of the method.

In particular, the first end la of each of the electronic component 1 is inserted into one of the holes 4 at the first surface 3a and the electronic component 1 is pressed into the hole 4 until the first end la protrudes from the second surface 3b by a predefined distance.

First, the container 6 is provided which comprises the slots 7. The container 6 is positioned on a mechanical press. Prior to step b., the electronic components 1 are arranged in the slots 7 of the container 6. Then, the carrier 3 is arranged on top of the container 6 such that the holes 4 of the carrier are aligned with the slots 7 of the container 6.

Next, the electronic components 1 are pressed into the carrier 3 by a tool 8, e.g. by a metal needle. Each electronic component 1 is pushed by one of the tools 8 out of the corresponding slot 7 of the container 6 and into one of the holes 4 of the carrier 3 aligned to the corresponding slot 7 of the container 6. By using a container 6 and tools 8 for pressing the electronic components 1 into the carrier 3, it is ensured that the electronic components 1 are pressed into the carrier 3 with a very small inclination. The slots 7 in the container 6 and the rectangular layout of holes 4 on carrier 3 guide a movement of the electronic components 1 such that the electronic components 1 move purely linear and such that it is prevented that the electronic components 1 are arranged at an oblique angle to the vertical axis 5 of the holes 4 in the carrier 3.

The electronic components 1 are pressed into the carrier 3 so far that they protrude from the second surface 3b of the carrier 3. The electronic components 1 are over-pushed such that they protrude from the second surface 3b by a distance which is longer than a later intended dipping length. The electronic components 1 are all arranged at the same level with respect to the second surface 3b of the carrier 3.

In step c. of the method, the electronic components 1 are pushed into the carrier 3 towards the first surface 3a. Step c. is also referred to as a push-back step. Pushing is done against a reference dipping plane 10 by over-pushing the carrier 3 into the reference dipping plane 10. After the electronic components 1 touch the reference dipping plane 10, they are physically moved upwards by further downwards motion of the dipping head in direction of the reference dipping plane 10. An "upwards" movement shall be understood as a movement towards the first surface 3a of the carrier 3. A "downwards" movement shall be understood as a movement in a direction opposite to the upwards movement.

By pushing the electronic components 1 by a defined distance back into the carrier 3 towards the first surface 3a, the levelling of the electronic components 1 can be made even more precise. In step c., the distance by which the electronic components 1 protrude from the second surface 3b of the carrier 3 is reduced. At the end of step c., the first end la of each electronic component 1 protrudes from the second surface 3b of the carrier 3 and the second end lb of each electronic component 1 protrudes from the first surface 3a of the carrier 3.

Step c. comprises the sub-steps cl and c2 wherein sub-step c2 is executed after sub-step cl. Sub-step cl is shown in Figure 5. In sub-step cl, the carrier 3 holding the electronic components 1 is mounted to a dipping head 9. The dipping head 9 is a mechanical holder configured to hold the carrier 3 and to move the carrier 3. The carrier 3 is mounted to the dipping head 9 such that the first surface 3a of the carrier 3 faces to the dipping head 9 and the second surface 3b of the carrier 3 faces away from the dipping head 9. The dipping head 9 comprises a mounting surface 9a and the first surface 3a of the carrier 3 is fixed to the mounting surface 9a.

A reference point or zero point for the dipping head 9 is a dipping head plane and overall thickness of the carrier 3.

Figure 6 shows the sub-step c2. In sub-step c2 of step c., the dipping head 9 holding the carrier 3 which holds the electronic components 1 is moved towards the reference dipping plane 10. The reference dipping plane 10 is a flat surface, e.g. a metal board. The dipping head 9 presses the electronic components 1 protruding from the second surface 3b of the carrier 3 against the reference dipping plane 10 such that the reference dipping plane 10 pushes the electronic components 1 by a defined distance back into the carrier 3 towards the first surface 3a of the carrier 3. This second pushing step improves the precision of the levelling of the electronic components 1.

In step d. of the method, the electronic components 1 are dipped into a paste. Prior to dipping, the paste is applied in even thickness on the reference dipping plane 10 against which second the pushing step is performed. Thereby a coating, which later forms a metallization 2a, is applied to the electronic components 1. As each electronic component 1 has the same distance from the carrier 3 relatively to the reference dipping plane, each electronic component 1 is dipped into the paste by the same dipping distance, resulting in identical coating length on all electronic components 1. The coating length is the length by which the electronic component 1 is covered by the paste. The paste is applied to the first end la of each of the electronic components 1 in step d.

During step d., the dipping head 9 holding the carrier 3 and the precisely arranged electronic components 1 is moved towards the reference dipping plane on which the paste has been applied. The paste is a metallic paste which forms the metallization 2a after drying. Then, the electronic components 1 are immerged into the paste by a defined dipping distance. The two-step pushing which has been made on steps b. and c. ensures an ideal levelling of the electronic components 1 in the carrier 3. This leads to minimizations of a deviation of the relative distance of the electronic components 1 versus the reference dipping plane lOprior to step d and minimization of geometrical tolerances of the metallization on the electronic components.

After step d. is completed, the applied paste is dried on the electronic components 1 in step e. and, thereby, the metallization 2a is formed. The metallization 2a forms a termination of the electronic components. In step f. of the method, the carrier 3 is separated from the dipping head 9 and is inverted. Then the carrier 3 is again fixed to the dipping head 9 such that the first surface 3a of the carrier 3 faces away from the dipping head 9.

In step g. the dipping head 9 is again used to dip the electronic components 1 being held in the carrier 3 into the paste. Thereby, the paste is applied to the second end lb of the electronic components 1 and the second metallization 2b is formed on the electronic components 1. Prior to the dipping process, the carrier 3 is again pressed into the reference dipping plane to ensure minimal deviations of the distance of the electronic components 1 versus the reference dipping plane.

Figure 7 shows an electronic component 1 after the method has been completed.

Reference numbers

1 electronic component la first end lb second end laa area for metallization lbb area for metallization

2a, 2b metallization

3 carrier

3a first surface of the carrier

3b second surface of the carrier

4 hole

5 vertical axis of the hole

6 container

7 slot

8 tool

9 dipping head

9a mounting surface

10 flat surface / reference dipping plane 11 metal layer 12 first layer of a soft material 13 second layer of a soft material