Printed Circuit Board for Electronics

The invention is directed to a printed circuit board for electronics, and particularly a printed circuit board formed of a flexible carrier material.

It is known to solder components onto a surface that carries the interconnects directly to the interconnects from above. This is referred to as the SMD technique (Surface Mounted Devices).

An object of the invention is to specify an easily automatable and heat-stable semiconductor contact both for linear as well as for planar semiconductor arrangements.

This is inventively achieved in an arrangement of the type initially cited wherein the interconnects are composed of a solderable metal or of a solderable alloy at least at the surface at which they can be connected to the components. The components, and particularly semiconductor chips, are then connected to the conductors by melting the solderable material.

FIG. 1 shows a perspective view of a contacted light-emitting diode in film technique;

FIG. 2 shows a row of 10 diodes in a pattern having a grid dimension of 0.5 mm;

FIG. 3 shows an example of an offset arrangement of 20 light emitting diodes in a row;

FIG. 4 shows a cross-section through a pluggable arrangement of the invention;

FIG. 5 shows an alphanumerical display in stacked technology;

FIG. 6 shows a cross-section through an element of a two-plane contacting; and

FIG. 7 shows a plan view of two elements in a 2-plane contacting.

A thin (approximately 1 .mu.m) copper layer 2 is applied (coated in currentless fashion or vapor-deposited) onto a flexible plastic carrier film 1 (for example polyethylene terephthalate, polymide, epoxy resin/fiberglass fabric). This copper layer 2 is subsequently galvanically reinforced to about 5 .mu.m. This reinforcement is necessary so that the interconnect structure can be etched and, moreover, it increases the heat elimination out of the contact zone. After the etching of the desired interconnects, an approximately 5 to 20 .mu.m thick tin layer 3 or some other solderable metal or a solderable alloy is likewise electro-deposited. The contacting of the component 4, which is a semiconductor chip and particularly a LED (light emitting diode) here, is performed with a solder-die after the crystal has been positioned at a metal-free region. One respective metal contact 6 for the semiconductor is arranged on interconnect 3. The insertion depth, the temperature of the crystal, and the pressure on the crystal can be set in a defined fashion with this solder die. The temperature must be selected such that the metal of the interconnect melts and the chip sinks into the carrier film for mechanical anchoring as shown at 100 in FIG. 1. The pn-junction of the semiconductor is referenced 5.

The geometry of the interconnects, and particularly their spacing is dependent on the dimensions of the semiconductors to be contacted, and is dependent on the desired current-loadability of the component 4.

However, it is also possible to etch and tin plate the interconnects on a Cu film laminated with a plastic film in order to contact the semiconductor chips. A further increase in the heat elimination can thus be achieved. However, the tolerances, and particularly the spacing of the interconnects and the thickness of the chips, must be extremely precisely observed.

The desired interconnect geometry for the contacting can also be etched in a solderable metal film (for example, tin film) that is laminated on a carrier film. No further work cycles are then required.

Constructing the interconnects of easily meltable layers is especially advantageous because additional techniques to prevent short-circuiting of the pn-junction of the semiconductor are not required. The melting ofthe metals (Sn or SnPb alloy) and of the plastic in the environment of the crystal also removes a Cu layer from the jeopardized zone in that these substances yield to the pressure of the crystal. A significant advantage in this type of contacting is that, in contrast to the nail-head bonding, only one work step is required in order to contact the p-side and the n-side. Moreover, this method offers the possibility of simultaneously contacting a plurality of crystals, or of contacting a semiconductor circuit comprising a plurality of terminals, in one work cycle.

It has proven especially advantageous for the alloy formation in the contact zone to use a semiconductor crystal that carries an additional gold layer 6 over the alloyed-in ohmic contacts.

The recited contacting is very suitable for a line arrangement, particularly given a slight spacing between the individual components, since a significantly tighter packing of the semiconductors is possible than in a traditional technique. As an example, a row of 10 diodes with a grid dimension pattern of 0.5 mm is shown in FIG. 2. An arrangement comprising 20 offset diodes with a grid dimension of 211 .mu.m is recited in FIG. 3. In case a pluggable component--both a discrete element as well as an arbitrary multiple row--is to be manufactured, it is possible to bring the plastic carrier into a shape on the basis of suitable methods (for example deep drawing or hot-pressing) to punch feet and to then solder the semiconductor in, as shown in FIG. 4. For better solderability of the feet 8, a film laminated with copper on both sides can be employed at these locations (FIG. 4). The arrangement shown in this FIG. 4 has an M shape such that the semiconductor component 4 is centrally soldered to the outer interconnects and is embedded in a casting compound 7. The inside interconnects are only provided for facilitating the solderability to the printed circuit board.

This technique offers particular advantages, and specifically for a light-emitting diode arrangement in a matrix form. This method, referred to as the stacked technique, for example results in an alpha-numeric display having 5.times.7 light-emitting diodes in a grid dimension of 1 mm, as shown in FIG. 5. Five carrier films each having 7 light-emitting diodes are thus arranged on top of one another and are secured such that a grid dimension of 1 mm also arises between the lines.

FIG. 6 shows a further possibility for manufacturing a matrix, whereby the leads to the light-emitting diodes are arranged on two sides of a thin plastic film 9. It is thus possible to solder a planar interconnect 11 to the gold layers 6 of the semiconductor at the inside in the contact zone, and to solder a lower interconnect 12 at the other side. For reinforcing, the carrier film comprising the two interconnect levels is glued onto a thick, insulating support 10. This technique, shown in FIG. 6 as a 2-plane contacting represents an interlayer connection. Here, too, the two metal coatings 6 of the semiconductor 4 are connected in one work cycle to the two leads 11, 12 on the two sides of the thermoplastic carrier film 9.

Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that I wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within my contribution to the art.