DE102016200098A1 - Conductive connection of laser-introduced signal conductors with paste-metallized pads on AlN substrates - Google Patents

Abstract

The invention relates to a method for applying metallizations on ceramic substrates (1), wherein the metallizations of pads (2) and signal conductor tracks (3) and the pads (2) have a greater thickness than the signal conductor tracks (3), and in In order to be able to inexpensively apply pads (2) with a large thickness and signal conductors (3) with a small thickness on a ceramic substrate (1) at least one method step, the following are to be carried out in sequence Procedural steps proposed: a. Use of a ceramic substrate (1) of aluminum nitride (AlN), b. Printing the pads (2) by screen printing using a screen with one or more printing operations, c. Introducing the signal conductor tracks (3) with a laser, wherein the laser beam is directed along the signal conductor tracks (3) to be created on the ceramic substrate (1) and by the heat of the laser beam at the location of the impact of the laser beam on the substrate (1) Aluminum nitride of the substrate (1) converts into the electrically conductive aluminum, d. simultaneously or after method step c, directing the laser beam onto the connection region (4) between the pads (2) and the signal conductors (3) to provide an electrically conductive connection region (4) electrically connecting the signal conductors (3) to the pads (4) conductively connects and e. optional galvanic application of a metallic coating on the pads (2) and the signal conductors (3).

Description

The invention relates to a method for applying metallizations on ceramic substrates, wherein the metallizations consist of pads and signal conductors and the pads have a greater thickness than the signal conductors, and in at least one method step metallizations are printed with the known screen printing process.

It is known to apply metallizations of any shape and size to ceramic substrates using a screen printing process and to provide these metallizations with a galvanically applied metallic coating.

Usually, the metallizations that are to conduct a high current later, must be made thicker. Hereinafter, these metallizations are referred to as pads. These pads can have any shape, such as round, square, rectangular or even band-shaped. In signal traces, however, only a small current is transmitted, so that the thickness of the signal traces may be low. Thickness is understood to mean the power line cross section. When both the high current carrying metallizations, i. The pads as well as the signal traces printed with a large thickness, this is expensive by the used basically unnecessary material.

In order to print both thin signal conductors and pads on a ceramic substrate, the signal conductors can be printed with a first sieve and the thick pads with a second sieve. This too is expensive by the use of two screens and thus two printing operations.

The invention has for its object to improve a method according to the preamble of claim 1 so that inexpensive pads can be applied with a large thickness and signal traces with a small thickness on a ceramic substrate.

• a. Verwendung eines keramischen Substrats aus Aluminiumnitrid (AlN),
• b. Aufdrucken der Pads mit dem Siebdruckverfahren unter Verwendung eines Siebs mit einem oder mehreren Druckvorgängen,
• c. Einbringen der Signalleiterbahnen mit einem Laser, wobei der Laserstrahl entlang der zu schaffenden Signalleiterbahnen auf das keramische Substrat gelenkt wird und sich durch die Wärme des Laserstrahls am Ort des Auftreffens des Laserstrahls auf das Substrat das Aluminiumnitrid des Substrats in das elektrisch leitende Aluminium umwandelt,
• d. gleichzeitig oder nach dem Verfahrensschritt c Lenken des Laserstrahls auf den Verbindungsbereich zwischen den Pads und den Signalleiterbahnen zur Schaffung eines elektrisch leitenden Verbindungsbereichs, der die Signalleiterbahnen mit den Pads elektrisch leitend verbindet und
• e. optional galvanisches Aufbringen eines metallischen Überzugs auf die Pads und die Signalleiterbahnen.

This object is achieved by a method according to claim 1. In order to inexpensively apply pads with a large thickness and signal traces with a small thickness to a ceramic substrate, the following sequential steps are recommended:

• a. Use of a ceramic substrate of aluminum nitride (AlN),
• b. Imprinting the pads with the screen printing process using a screen with one or more printing operations,
• c. Introducing the signal conductor tracks with a laser, wherein the laser beam is directed onto the ceramic substrate along the signal conductor paths to be created and the aluminum nitride of the substrate is converted into the electrically conductive aluminum by the heat of the laser beam at the location of the impact of the laser beam on the substrate,
• d. simultaneously or after the method step c, directing the laser beam onto the connection area between the pads and the signal conductor tracks to create an electrically conductive connection area which connects the signal conductor tracks to the pads in an electrically conductive manner and
• e. optional galvanic deposition of a metallic coating on the pads and signal traces.

In method step d, the laser beam is preferably directed onto the adjacent pad starting from the signal conductor tracks. As a result, the melting range can be sharply demarcated.

In an inventive embodiment, the metallic coating consists of gold or silver.

In an advantageous embodiment, sections of the signal conductor tracks with a smaller current line cross-section than the surrounding signal conductor tracks are formed in order to create resistors integrated in the signal conductor tracks.

In the power electronics, the power-carrying circuit elements are preferably printed and the signal lines are lasered.

A ceramic substrate according to the invention with metallizations comprising pads and signal conductor tracks, wherein the pads have a greater thickness than the signal conductors, and with an electrically conductive connection region of the pad to the signal conductor, is characterized in that the ceramic consists of aluminum nitride and on the signal conductor in the Connection area molten metal of the pad is located.

The signal conductors according to the invention consist of electrically conductive aluminum. At least directly on the substrate. The aluminum can be constructed by other metals.

The invention will be further described with reference to four figures.

According to the invention, a ceramic substrate 1 made of aluminum nitride (AlN). 1 shows this substrate 1 , On this substrate 1 made of AlN are in a first step pads 2 , ie metallizations, which are to have a large thickness, printed with a screen printing process. This can also be done by multiple printing operations. 2 shows this substrate 1 with the printed pads 2 which in the case shown consist of two layers.

Subsequently, in a third process step (see 3 ) introduced with a laser, the metallizations, which later as signal conductors 3 serve. For this purpose, as in WO 2013/072457 A1 described (hereinafter also referred to as embedded method), the laser beam along the signal conductors to be created 3 on the substrate 1 directed. The heat of the laser beam changes at the location of the impact of the laser beam on the substrate 1 convert the aluminum nitride into the electrically conductive aluminum.

In a fourth method step, which is preferably connected to the third method step, the laser beam is applied to the connection area between the pads 2 and the signal traces 3 steered and so an electrically conductive connection area 4 created the signal traces 3 with the pads 2 electrically conductive connects.

In a preferred embodiment, the laser beam, starting from the signal conductors 3 , on the adjacent pad 2 directed. As a result, the metallization of the pad melts under the laser beam 2 and flows to the adjacent signal trace 3 , The connection area 4 is the area on the pad 2 which was irradiated by the laser beam and the area on the signal traces 3 with which the molten metallization of the pad connects. 3 shows the connection area 4 only schematically.

In an optional fifth process step (see 4 ) becomes a metallic coating of, for example, gold or silver on the pads 2 and the signal traces 3 applied.

For power electronics, tracks of thick cross-section are used to conduct high currents, and thin signal traces 3 to conduct control signals.

When using printed signal conductors 3 costs arise for paste, which can be saved by the described embedded process.

However, via the embedded method, no signal conductors can be used 3 be produced with large cross-section, which are necessary to conduct high currents. In order to produce such components cost-efficiently, it is necessary according to the invention to combine both methods.

Without the method described by the invention, it is not possible to combine these two methods. According to the invention on the AlN ceramic by the overlap of laser-introduced signal conductors 3 with paste-metallized structures (pads 2 ) a conductive connection area 4 created.

So far, there are some problems with the use of paste metallised signal traces. In the sense of 3iP (power electronics), in which current-carrying thick metallizations are combined with thin signal lines, it can lead to additional costs (use of several different screens) and problems in the choice of metallization paste (signal lines were executed only in base paste, which causes problems in lead the galvanic treatment).

In the method according to the invention, it saves the screen and the paste for the signal lines and the resulting Al layer is easy to build galvanic.

For the purposes of light applications in which solder resists are used, there is the problem that the height difference between the ceramic and the metallization surface does not allow a uniform thickness of the solder resist to be realized. The solder pads to be spared are left free in the invention. The lotstopplackbedeckten tracks are very flat, resulting in a uniform layer thickness of the paint. Likewise also Metallisierungspaste is saved.

The resulting by the laser beam signal trace (aluminum trace) has a certain resistance. This can be further reduced by galvanic structures. With a suitable layout, it is thus possible to integrate certain resistances directly into the printed circuit board.

A problem which still occurs in the case of the directly lasered printed conductors is a fluctuating adhesion when soldering the parts. This is relativized by the printed soldering / bonding pads.

The invention thus describes the joining of metallization pads on AlN ceramic with laser-fabricated galvanized signal conductor tracks. With laser introduced signal traces can be used for example as a control circuits for thick metallized signal conductors (power electronics) or as a connection between solder or bond pads. This method can be used to create individual signal traces without sieving and paste costs, or to save paste by eliminating the control circuitry.

For power electronics, the control circuits are currently printed with a thin layer of paste and the power-carrying circuit parts are further built with thick metallization. This requires at least two different sieves and there may be problems regarding the selection of pastes (including thickness of the base / top paste, galvanizability).

For light applications, the complete layout is printed. Here, however, it can often lead to the use of solder masks problems because of the height of the signal traces (height difference between signal traces and ceramic)

According to the invention, in the power electronics, the power-carrying circuit elements are printed and the signal lines are lasered. It eliminates the use of different sieves.

In light applications, the parts of the signal conductors on which are bonded or soldered are applied with paste and the remainder introduced with laser. The solder mask can then easily be printed on the signal traces, as they have almost no increase.

The length and type of galvanic treatment can also be used to regulate the resistance of the resulting signal conductors.

The process is the complete processing of the metallization until shortly before electroplating, insertion of the lasered signal conductors with an overlap on the metallization pads, ultrasonic cleaning or brushes to remove the smoke and subsequent electroplating (Ni / Au)

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2013/072457 A1 [0015]

Claims (7)

Method of applying metallization to ceramic substrates ( 1 ), wherein the metallizations of pads ( 2 ) and signal conductors ( 3 ) and the pads ( 2 ) has a greater thickness than the signal conductors ( 3 ), and in at least one process step, metallizations are printed with the screen printing method known per se, characterized by the following process steps to be carried out in sequence: f. Use of a ceramic substrate ( 1 ) of aluminum nitride (AlN), g. Imprinting the pads ( 2 ) by the screen printing method using a screen with one or more printing operations, h. Introduction of the signal conductors ( 3 ) with a laser, wherein the laser beam along the signal conductors to be created ( 3 ) on the ceramic substrate ( 1 ) is guided by the heat of the laser beam at the location of the impact of the laser beam on the substrate ( 1 ) the aluminum nitride of the substrate ( 1 ) converted into the electrically conductive aluminum, i. simultaneously or after method step c, directing the laser beam onto the connecting region ( 4 ) between the pads ( 2 ) and the signal traces ( 3 ) to provide an electrically conductive connection area ( 4 ), the signal traces ( 3 ) with the pads ( 4 ) electrically conductively connects and j. optional galvanic application of a metallic coating on the pads ( 2 ) and the signal traces ( 3 ). Method according to Claim 1, characterized in that, in method step d, the laser beam originates from the signal conductor tracks ( 3 ) on the adjacent pad ( 3 ) is directed. A method according to claim 1 or 2, characterized in that the metallic coating consists of gold or silver. Method according to one of claims 1 to 3, characterized in that for the creation of in the signal conductors ( 3 ) integrated resistors sections of the signal traces ( 3 ) with a smaller power line cross-section than the surrounding signal conductors ( 3 ) be formed. Method according to one of Claims 1 to 3, characterized in that the power-carrying circuit elements are printed in the power electronics and the signal lines ( 4 ) are lasered. Ceramic substrate ( 1 ) with metallizations of pads ( 2 ) and signal conductors ( 3 ), whereby the pads ( 2 ) has a greater thickness than the signal conductors ( 3 ) and with an electrically conductive connection region ( 4 ) of the pad ( 2 ) to the signal conductor track ( 3 ), characterized in that the ceramic consists of aluminum nitride and on the signal conductor ( 3 ) in the connection area ( 4 ) molten metal of the pad ( 2 ) is located. Substrate according to Claim 6, characterized in that the signal conductors ( 3 ) consists of electrically conductive aluminum.

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