DE4446289C2 - Process for the micro connection of contact elements - Google Patents

Description

The present invention relates to a method according to the The preamble of claim 1 and claim 2.

Methods of the above type are used in the microverbin manure technology in the field of flip-chip technology in particular in the mass production of systems with multi-pin chips set. With this flip-chip contact, the chip is connected the contact elements designed as connection surfaces below on a sub also provided with connection surfaces strat upset. The connection between the pads of the chip and the pads of the substrate can on un different ways, for example by welding, Soldering or gluing. Especially when using Micro welding process for connecting the pads with however, each other results either from the application the chip with pressure and heat (solid-state welding process) or heat (fusion welding process) an unfavorable pressure and / or heat stress for the chip. This results in one Chen cases that special heat sinks on the above back of the heat-dissipating chips have to.

In other cases, such as contacting polyester foil with printed circuit boards on circuit boards shows a desirable analog application of the Flip chip technology due to the low decomposition temperature rature of the polyester carrier as impossible.  

From JP 4-91 493 A in: "Patent Abstracts of Japan", 1992, Sec. E-1232, vol. 16 / no. 318, is a process for thermi The connection between two arranged on a substrate ter contact elements known by means of a solder material that in the area between the contact elements of the substrates located. To generate the necessary for the thermal connection The connection temperature will be opposite to each other gend arranged contact elements from the back of a transparent, flexible substrate with laser radiation strikes. The laser radiation passes through the transparent Substrate through to the contact elements and thus leads to egg melting of the arranged between the contact elements ten solder material.

US 3,374,531 shows a method for thermal connection formation of contact elements of two substrates, in which one as Energy or heat sink device is used, the temperature generated by an infrared radiation source in a flexible substrate.

DE 35 44 377 A1 shows a method for connecting a Semiconductor with connecting wires, in which a laser welding head is used.

From GB 2 068 645 A a method is known in which a Contacting electrical conductors using an electrical conductive adhesive.

DE 42 00 492 A1 finally describes a method that the thermal connection of two contact elements by means of one broken into the joint by an optical fiber treated with laser radiation.

The present invention has for its object a ge compared to the known method for thermal connection with rearward laser exposure through a transparent sub strat to propose a further developed procedure that effectiveness.

This task is accomplished by a process with the characteristics of  Claim 1 or claim 2 solved.

In the method according to the invention, the the necessary connection temperature in the connection level Applying a substrate to its contact elements opposite back forth with a radiation. Here are the radiation in terms of their wavelength and the measure material of the substrate in terms of its transparency coordinated with each other that the radiation essentially through the substrate is passed through and absorption of the Radiation in the area of the connection level, ie in the area of the Contact elements, is done.

The invention is based in a known manner on the transfer of radiation energy through the substrate to the con the transparency properties of the substrate to use to absorb the radiation energy in the substrate to minimize and thus a conversion of the radiation energy in heat energy required for the connection process essentially can only be achieved in the connection area itself. In the opposite Set to the well-known flip-chip technology, in which the heat conduction properties of the substrate to the junction ge are used and their application therefore corresponds with a is connected to the thermal stress of the substrate, is the thermal stress on the substrate on a Mi nimum is reduced and essentially depends on how high after appropriate adjustment of radiation wavelength and substrate material the residual degree of absorption of the substrate materials.

According to claim 1 there is a solution according to the invention in covering the connecting material with a coating provided that abge on the wavelength of the radiation has a certain degree of absorption.

According to claim 2, there is a further Lö according to the invention solution in at least facing the connection area th surface of the radiation source opposite ordered substrate to provide a coating that the Radiation reflected in the connection plane. Here is already  due to the repeated passage of the radiation through the Connection level for the required absorption effect ge worries.

It proves to be particularly advantageous if radiation is a Laser radiation is used because the selection of a suitable one Lasers in addition to the exact setting of the desired waves length also an exact adjustment in the connection put introduced radiation energy, for example by Pulse mode, enables.

Basically, in addition to the use of a laser arrangement comes as Radiation source the use of any radiation source as long as it is ensured that the substrate material and the material of the contact elements or the zwi connecting material arranged between the contact elements are coordinated that in the substrate material in we noticeable a transmission and in the contact elements pull the connection material essentially an Ab Sorption of the radiation energy takes place.

With a device suitable for carrying out the procedures a radiation source can be on the back of the substrate Emission of radiation with a defined wavelength is arranged be net, such that the radiation through the substrate to Ab sorption in the connection plane between the substrates will wear.

If a device is used to carry out the method sets, as known from DE 42 00 492 A1, the light fiber optic technology for introducing laser radiation into the ver Binding site used, contact elements one and the same substrate over different optical fibers with under different laser radiation are applied to the radiation energy supplied to respective contact elements visually their wavelength and strength to the specific To be able to adjust conditions.

A variant of the method according to the invention is described below rens showing two embodiments of a front Direction for performing the method based on the drawing nations explained in more detail. Show it:

. Figure 1 shows the connection between a chip and a circuit board;

Fig. 2 shows the connection between a polyester film provided with conductor tracks and a circuit board.

Fig. 1 shows a schematic representation of the connection between a chip 10 and a circuit board 11 by means of a not further shown here, the laser source, the laser radiation 12 is transmitted through an optical fiber 13 to the back 14 of the chip 10. Here, the chip 10 with its connection surfaces 15 , which have been seen here previously to form bumps 16 with a contact metallization of connecting material 17 , on conductor tracks 18 of the circuit board 11 . Before carrying out the connection, the bumps still have their characteristic hump shape, which is shown in dashed lines in FIG. 1.

Although in Figs. 1 and 2, the contact elements are designed as pads or conducting tracks are formed, it is equally possible to carry out the method illustrated variant herein with reference to particular execution, if the on-circuit surfaces as a single conductor, as for example, wire conductors, are formed. Basically, the procedure described here can be used regardless of the configuration of the connection pads.

The circuit board 11 lies on a mounting platform, not shown in detail here, symbolized by supports 19 , 20 , which can be moved, for example, under the optical fiber 13 in the direction of the arrow 21 .

The optical fiber 13 has an end cross section 22 , which covers the area of all pairings between the connection areas 15 of the chip 10 and the conductor tracks 18 of the circuit board 11 .

If the chip 10 previously placed in a manner not shown here on the circuit board 11 is in the relative positioning shown in FIG. 1 with respect to the end cross-section 22 of the optical fiber 13 , as shown in FIG. 1, the chip is acted upon 10 from the rear with laser radiation 12 .

Using a laser radiation with a wavelength of 1064 nm, silicon has a absorption of approximately 5% as the carrier material for the chip 10 . If essentially tin is chosen for the connecting material 17 of the bumps 16 , this has an absorption of approximately 35%. As a result, these three parameters lead to a temperature distribution with the result that there is a relatively low heating and thus low thermal stress on the chip 10 and the connection temperature 15 required for the thermal connection of the connection surfaces 15 of the chip 10 with the conductor tracks 18 of the circuit board 11 essentially is achieved only in the area of a connection level 23 .

As further shown in FIG. 1, the end cross section 22 of the optical fiber 13 is arranged at a distance a from the rear side 14 of the chip 10 , so that the chip 10 is exposed to radiation energy without contact. This results in a further advantage over the conventional flip-chip technology, in which the chip is held in position on the board during the connection process. Because of the surface tensions that occur in the molten state of the bumps 16 in the bump surface, which often lead to a hy perboloid-shaped formation of the bumps during the remelting process, an associated self-alignment effect (self-alignment) for the precise alignment of the chip 10 on the circuit board 11 can be achieved or use the connection surfaces 15 opposite the conductor tracks 18 . Therefore, the requirements that have to be made regarding the accuracy of a pick-and-place device for positioning the chip 10 on the circuit board 11 before the actual connection process is carried out can be considerably reduced.

Fig. 2 shows a variant of the device shown in Fig. 1 Before, in which the emerging from the end cross section 22 of the optical fiber 13 emerging laser radiation 12 is used for connection between a conductor track 24 provided with flexible polyester film 25 and a connection surface 26 having board 27 . In accordance with the embodiment shown in FIG. 1, here is the board 27 on a mounting platform symbolized again by the supports 19 , 20 . In contrast to the exemplary embodiment shown in FIG. 1, however, the end cross section 22 of the optical fiber 13 is arranged below a rear side 28 of the circuit board 27 . The board 27 has a transparent carrier material, so that the laser radiation 12 emitted from the end cross section 22 of the optical fiber 13 can reach the connection plane 23 between the board 27 and the polyester film 25 without substantial absorption, in order to be analogous to that in FIG. 1 Embodiment shown here in bumps 29 formed here on the pads 26 of the board 27 to be substantially absorbed.

In the arrangement shown in FIG. 2, the extremely temperature-sensitive polyester film 25 is based on the direction of the laser radiation 12 on the rear side of the connection plane 23 . This leads to the fact that the thermal loading of the polyester film 25 is extremely low, so that thermal decomposition phenomena of the polyester film 25 , which until long made a welded connection of conductor tracks 24 with polyester films 25 appear practically impossible, no longer occur.

Although in both of the above-described embodiments always use laser radiation to apply energy was used, and the connection as a welded joint are basically also others Energy radiation or light radiation, such as also strong halogen light, can be used to the described Way connections between two with pads to provide provided substrates. With these connections can also be soldered or adhesive connections.

In addition, it should be noted that this is an example method described in a single-bond procedure ren, in which a successive contacting the one individual pad pairings takes place, as well as so-called called gang bonding method is feasible, in which one synchronous contacting of the pad pairs takes place.

Claims (3)

1. A method for the thermal connection of two electrical contact elements arranged on each substrate by means of an electrically conductive connecting material, the substrates being arranged for carrying out the connection such that the contact elements lie opposite one another in the connection plane and the contact elements to achieve the connection temperature by a Radiation through transparent substrate can be acted upon, characterized in that a coating having an absorption capacity tuned to the wavelength of the radiation ( 12 ) is applied to the connecting material. 2. A method for the thermal connection of two electrical contact elements arranged on a respective substrate by means of an electrically conductive connecting material, the substrates being arranged to carry out the connection such that the contact elements lie opposite one another in the connection plane and the contact elements to achieve the connection temperature by a transparent substrate to pass pressurized lung with a Strah, characterized in that at least on the junction plane (23) facing surface of the opposite of ordered substrate a coating for Re flexion of the radiation into the connecting plane (23) is arranged the radiation source. 3. The method according to claim 1 or 2,  characterized, that laser radiation is used as radiation.