DE102016108656A1 - Power electronic assembly with vibration-free contacting - Google Patents

Abstract

A power electronic assembly comprising a substrate, a semiconductor disposed on the substrate, a semiconductor body contacting the semiconductor, and an electrical conductor contacting the metal body, characterized in that the electrical conductor is contacted to the metal body by laser welding.

Description

The invention relates to a power electronic assembly with vibration-free contact. More particularly, the invention relates to a power electronic assembly comprising a substrate, a semiconductor disposed on the substrate, a metal body contacting the semiconductor, and an electrical conductor contacting the metal body.

Such a power electronic assembly is for example from the EP 2 766 922 A1 known.

In principle, power devices carry a very high current, for example from 20 to 250 A, and thereby develop a very high current density of about 150-200 A / cm 2. Modern power semiconductors also make it possible to switch at very high frequencies, which usually leads to overvoltages in the voltage curves, especially in the steep switching edges of the current increase at power-up due to the conductor track guidance usually occupied by parasitic inductances. In addition, the high frequency components in the switching edges partly lead to a displacement of current in the conductors, which is known as the skin effect.

Modern power modules must therefore take into account the high current density, the overvoltages and possibly the skin effect by suitable design and by sufficiently current-carrying designed line and connection cross-sections.

In particular with regard to the low-inductive contacting of power semiconductors, so-called planar build-up technologies are quite advantageous. For this purpose, for example, a structure is known, which has been attached to the power semiconductors by galvanic plating and has these connections via an insulation layer. This technique enables very low-inductive connection geometries, but is severely limited in terms of current carrying capacity - especially when the skin effect occurs. Also, this process with high costs to book, so that a dissemination of this technique has been missing.

A similar approach is followed by the so-called "embedding technique" of power semiconductors in printed circuit boards. Also in this method, the top-side terminals of the semiconductors are formed by electroplating. Similar limitations apply here.

Both methods are only economical from very large production volumes and very cost-intensive for design changes and for small batches.

In contrast, traditional contacting using Al wire bonds is increasingly reaching the limits of current carrying capacity of Al wires in modern power modules. These are no longer able to carry the current in ever smaller semiconductors with ever higher current density. In addition, in order to achieve a sufficient thermo-mechanical load capacity, they must be designed with comparatively high loops. In turn, a large loop height results in unwanted parasitic inductance.

The same applies to ribbon bonding by means of ultrasound-supported bonding methods:
Both in wire bonding and ribbon bonding, the friction welding contacts provide a "bottle-neck" for the current flow. Wires or ribbon bonded directly to the thin semiconductor metallization can hardly absorb enough current through the thin semiconductor metallization and the often too small metallic pad an increased resistance and a local thermal overload is the result.

The object of the invention is therefore to provide a semiconductor Oberseitenkontaktierung with the highest possible current carrying capacity for switching with steep rising edges.

According to the invention, therefore, a power electronic assembly is provided with a substrate, a semiconductor disposed on the substrate, a metal body contacting the semiconductor, and an electrical conductor contacting the metal body, wherein the electrical conductor is contacted to the metal body by laser welding.

The electrical conductor is preferably a ribbon or a stranded wire, that is to say an electrical conductor consisting of thin individual wires.

Particularly preferably, the electrical conductor made of aluminum (Al) or copper (Cu) or a predominantly aluminum (Al) or copper (Cu) containing alloy or a aluminum (Al) and copper (Cu) containing layer material.

According to a further preferred embodiment, the metal body is contacted on the semiconductor by means of sintering.

Finally, it is preferably provided that the loop height of the electrical conductor is at least 0.025 mm and at most 1 mm.

Furthermore, a method for manufacturing a power electronic assembly is claimed, comprising a substrate, a semiconductor disposed on the substrate, one on the semiconductor arranged, the semiconductor contacting metal body and an electrical conductor contacting the metal body, wherein the contacting of the electrical conductor on the metal body is effected by means of laser welding.

Preferably, the electrical conductor used to contact the semiconductor is a ribbon or a stranded wire.

Particularly preferably, the electrical conductor consists of aluminum (Al) or copper (Al) or a predominantly aluminum (Al) or copper (Cu) -containing alloy or a aluminum (Al) and copper (Cu) -containing layer material.

Finally, the metal body is contacted with the semiconductor by sintering.

A first basic idea of the invention is to utilize a largely full-area contacting of the power semiconductor with a metal plate, preferably of an electrically and thermally highly conductive material such as copper (Cu), in order to initially enable a very good current distribution on the power semiconductor and local thermal overloads to avoid the power semiconductor. The metal plate is preferably connected to the power semiconductor by sintering using sintering paste (eg, Ag sintered paste).

Instead of the copper wires usually to be used for contacting the power semiconductor to the outside, a metal strip or ribbon (preferably also made of Cu) is preferably applied to the metal plate. However, the metal strip is not bonded as usual with ribbon bonding with a high loop, but is performed as flat as possible to the second contact point in order to have a very small contribution to the parasitic inductance. Ribbons are commonly used for high frequency contacts to effectively counteract the skin effect.

The flat loop guidance of the tapes has the disadvantage in an ultrasound-supported bonding process that alone the ultrasound friction movement is strongly attenuated uncontrollably at the latest at the second contact point by the little elastically guided ribbon. The lower the loop height of the contact strip, the higher its rigidity and the tendency to concentrate the mechanical stress on the joint. A weld of unknown quality would be the result.

Another advantage of the invention is therefore to use the vibration-free contacting by means of laser welding in order to achieve a minimum loop height for a minimum, parasitic inductance. Since the energy input is by laser energy and not by ultrasound-induced vibrations, the welding energy can be applied to both terminals of the flat ribbon in a controlled manner, although the ribbon has maximum rigidity due to the small loop.

Another known disadvantage of the ultrasound-supported bonding technique is also avoided: The sintered connection of the metal plate on the power semiconductor is not "shaken loose".

Very advantageous in laser welding technology for tapes is the ability to achieve a very full-surface welded joint. This is only possible with ultrasound-based connection technology with very well adapted tool geometry and process control and is mainly used on the power semiconductor to the o. G. Abolish the sintered compound can cause.

Instead of a ribbon in the form of a metal strip can also be very advantageous compounds produced by stranded wire. The connection of the strand to the contact points is insufficiently possible by ultrasound-assisted methods. Known is a compound of the strand by soldering or by silver sintering (own patent or publications). However, these methods adhere to disadvantages in the automation of the process control. Here, the use of laser welding technology is very beneficial.

The woven structure of the strand offers over the solid material structure of a ribbon the advantage of elasticity under thermo-mechanical loads. The strand can deform in the plane, whereas a ribbon can only draw the elasticity from a certain expansion reserve through the loop guide.

The flat loop guidance of the laser-contacted ribbon or strand, however, places increased demands on the insulation, in particular of chip edges. Flash-overs are therefore absolutely to be avoided.

A particularly preferred method is to allow the carrier film of the top chip contact to overlap circumferentially around the chip. Thus, an effective isolation of the flat-guided bands to the chip edges can be achieved safely.

Another method for bringing about the required isolation between ribbon and external potential on the bridged semiconductor and substrate is to produce a contour-conforming insulation layer prior to laser contacting. The insulating layer extends from the edge of the semiconductor contact area via the semiconductor edge and the conductor surface of the substrate to the open contact surface of the second laser-contacted ribbon "landing site". An exemplary insulating layer is sold under the trade name Parylene ^® (trademark Union Carbide) displaced coating methods and materials or films of the material Kapton ^® (brand name of DuPont).

With secure loop guidance of the ribbons, the usual silicone soft encapsulation, which is applied after welding, of power modules is sufficient to ensure the insulation.

Basically, for the loop height of the laser-contacted, low-inductive ribbon, the desired minimum height of the ribbon from the external potential is determined by the insulation resistance of the volume below the ribbon. In particular, the coating with the material Parylene ^® allows a small layer thickness (depending on the insulation requirements of the application) and thus a low, low-inductive loop design.

For example, the electrical breakdown strength of Parylene N ^® is higher than 200V / micron film thickness. For a semiconductor with a blocking capability of, for example, 1200 V, a loop height of a few 10 μm can therefore be achieved with a layer thickness of 6 μm and particularly preferably additionally a safety impact of factor 2-5 (corresponding to approximately 30 μm) (from approx microns). This low loop height allows the achievement of very low parasitic inductances for each laser contacted ribbon over a Parylene ^® insulation layer.

Similar insulation strengths and thus comparable loop heights are also equipped with Kapton ^® (polyimide) film as the distance (> 200 V / micron film thickness from 25 microns).

The invention will be explained in more detail below with reference to exemplary embodiments illustrated in the attached drawings and particularly preferred embodiments. Show it:

1 the schematic structure of a particularly preferred designed power electronic assembly according to the invention; and

2 a flowchart for the process flow for the production of power electronic assembly from 1 ,

1 shows the schematic structure of a particularly preferred designed power electronic assembly according to the invention.

In particular shows 1 a power electronic module 10 with a substrate 20 , one on the substrate 20 arranged semiconductors 30 one on the semiconductor 30 arranged, the semiconductor 30 contacting metal body 40 and one the metal body 40 contacting electrical conductor 50 , According to the invention, the electrical conductor 50 with the metal body 40 contacted by laser welding. Likewise, the electrical conductor 50 contacted with the not further identified substrate connection by means of laser welding.

The illustrated electrical conductor 50 is preferably formed as a ribbon or as a strand and is particularly preferably made of aluminum (Al) or copper (Cu) or a predominantly aluminum (Al) or copper (Cu) -containing alloy or a aluminum (Al) and copper (Cu) containing layer material.

As in 1 indicated is the metal body 40 on the semiconductor 30 contacted by sintering.

Striking is also the flat structure of the 1 shown power electronic assembly 10 , which is achieved in particular by the loop height LH of the electrical conductor 50 at least 0.025 mm, but at most 1 mm. The electrical conductor 50 therefore has a substantially elongated conformation.

The flat loop of the electrical conductor 50 requires isolation from the semiconductor 30 , in the 1 through the between semiconductors 30 and electrical conductor 50 arranged insulation layer 60 is effected.

2 shows a flowchart for the process flow for the production of the power electronic module 1 ,

In a first step 100 becomes the semiconductor 30 on the substrate 20 arranged. At the same time in this step already a fastening of the semiconductor 30 done on the substrate.

In a second step 110 becomes the metal body 40 on the semiconductor 30 arranged and at the same time an electrical contact between semiconductors 30 and metal body 40 produced. In this step, at the same time an attachment of the metal body 40 with the semiconductor 30 and an attachment of the semiconductor 30 take place on the substrate, as far as the latter is not in step 100 has been made.

In step 120 becomes - as already mentioned above - the free surface of the semiconductor 30 with an insulation layer 60 For example, from Parylene or Kapton or other material, covered.

Finally, in step 130 the metal body 40 with the electrical conductor 50 contacted by laser welding.

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

• EP 2766922 A1 [0002]

Claims (9)

A power electronic assembly comprising a substrate, a semiconductor disposed on the substrate, a semiconductor body contacting the semiconductor, and an electrical conductor contacting the metal body, characterized in that the electrical conductor is contacted to the metal body by laser welding. Power electronic assembly according to claim 1, characterized in that the electrical conductor is a ribbon or a stranded wire. Power electronic assembly according to one of the preceding claims, characterized in that the electrical conductor of aluminum (Al) or copper (Cu) or a predominantly aluminum (Al) or copper (Cu) containing alloy or an aluminum (Al) and copper (Cu) containing layer material. Power electronic assembly ( 10 ) according to one of the preceding claims, characterized in that the metal body is contacted on the semiconductor by means of sintering. Power electronic assembly according to one of the preceding claims, characterized in that the loop height of the electrical conductor is at least 0.025 mm and at most 1 mm. A method of manufacturing a power electronic assembly comprising a substrate, a semiconductor disposed on the substrate, a semiconductor body contacting the semiconductor, and an electrical conductor contacting the metal body, characterized in that the contacting of the electrical conductor to the metal body is by laser welding , A method according to claim 6, characterized in that the electrical conductor is a ribbon or a stranded wire. Method according to one of claims 6 and 7, characterized in that the electrical conductor of aluminum (Al) or copper (Al) or a predominantly aluminum (Al) or copper (Cu) containing alloy or an aluminum (Al) and copper (Cu ) containing layer material. Method according to one of claims 6 to 8, characterized in that the contacting of the metal body with the semiconductor is carried out by sintering.

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