DE4446289A1 - Contact elements on micro-chip boards are connected together by heating a joining element between the contact element - Google Patents

Abstract

Substrates with contact elements (15,18) are arranged opposite each other with joining material (17) in between. Beam energy (12) is applied to the assembly from one side of either of the substrates (14,11) and caused to focus in a plane (23) located between the two substrates. At this point the beam energy is absorbed. The wavelength of the beam and the transparency of the substrates are chosen such that the beam passes through the substrate and is absorbed in the plane (23).

Description

The present invention relates to a method and a Device for the thermal connection of two on each a substrate arranged contact elements by means of a Connection material, whereby to carry out the connection the substrates are arranged so that the Kon Cover clock elements in a connection level and to Achievement of the necessary connection in the connection level temperature a substrate from its against the pads overlying back is energized.

Methods and devices of the above type are in the Micro connection technology in the field of flip-chip technology especially in the mass production of systems with high pin chips used. With this flip-chip contact the chip with the cones formed as pads clock elements down on a also with pads provided substrate applied. The connection between the Pads of the chip and the pads of the sub strats can be in different ways, for example by welding, soldering or gluing. Especially at Use of micro welding processes to connect the An end faces with each other, however, result either from the application of pressure and heat to the chip (solid welding process) or heat (fusion welding process) unfavorable pressure and / or heat stress for the chip. In some cases, this leads to special heat sinks  on the top of the heat dissipating chips must be mounted.

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.

The present invention is therefore based on the object to create a method or a device, that enables a micro-connection of contact elements light like the flip-chip technology from the back of a substrate provided with contact elements takes place without that, however, ver the disadvantages described above are bound.

This task is accomplished by a process with the characteristics of Claim 1 or a device with the features of the Proverb 3 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 therefore makes use of the basic idea of the transmission of radiation energy through the substrate the transparency properties of the sub to use strats to absorb the radiation energy in the To minimize substrate and thus a transformation of the beam energy in the thermal energy required for the connection process to be achieved essentially only in the connection area itself. In contrast to the well-known flip-chip technology, in which the  Thermal conductivity properties of the substrate to the junction are used and their application therefore with a corresponding appropriate thermal stress on the substrate, the ther Mixing stress on the substrate is reduced to a minimum and essentially depends on how high it corresponds to appropriate coordination of radiation wavelength and substrate material is the residual degree of absorption of the substrate material.

One way to ensure that in the field of conn level of absorption required for connection Radiation occurs by pre-connecting material watch the one on the wavelength of the radiation has a certain degree of absorption.

Alternatively or in addition to the above measure can also achieve the desired absorption effect be made by connecting the material with an absorption Coating is provided, the one on the wavelength of Radiation matched absorption.

Another way to get the required absorption effect to provide is to at least on the verbin area facing away from the beam arranged source a reflection coating device to provide the radiation in the connection plane reflected. Here is already due to the repeated through gangs of radiation through the connection level for the expl absorption effect.

It proves to be particularly advantageous if as radiation source a laser source is used because the selection of a suitable laser in addition to the exact setting of the desired th wavelength also an exact setting of the ver Binding point introduced radiation energy, for example wise through pulse operation.

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.

In the device according to the invention is on the back of the sub strat a radiation source to emit radiation with defined wavelength arranged such that the radiation through the substrate for absorption in the connection plane between is transferred to the substrates.

When the radiation source is designed as a laser source in a laser arrangement can have a light guide have at least one optical fiber for transmission the laser radiation on the back of the substrate is used. The Allows the use of such a light guide device an exact positioning of the Beam exit cross-section to connect with each other the contact elements of the substrates. In the event that the Light guide device has a plurality of optical fibers, the with regard to their number, arrangement and their exit cross cuts the pairings intended for connection with each other of pads correspond, it is even possible to load impact of the substrate with radiation energy on the with areas of the substrate provided with the contact elements restrict. In addition, in the event that there is a difference Lich trained contact elements on the same sub strat or different, applied to it Connection materials have different absorption coefficients ten have created the opportunity that each Radiation energy supplied to contact elements with regard to their wavelength and height to the specific conditions adapt. This can be achieved, for example, by that the respective optical fibers have different lasers sources are assigned.

In the case of using a laser source as the radiation source  there is another possibility of training the Laseran order in this with a focusing device for focus sation of the laser radiation in the connection plane or a Focus plane at a predetermined distance from the connection level. This design of the laser arrangement has the Advantage that the distance to the connection level in the Connection level desired energy density and thus that in the The resulting connection temperature affects the connection level can be.

Of course, such a focus with the ver tied benefits not necessarily with use connected to a laser arrangement. Rather, a Fo kissing advantageous for any type of radiation deploy.

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. The chip 10 lies 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 surfaces 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 . The wavelength of the laser radiation is so matched to the carrier material of the chip 10 that, in gross simplification, the temperature profile shown in FIG. 1 in the area of the connecting elements, that is to say the chip 10 and the circuit board 11 , is set. When a laser radiation with a wavelength of 1064 nm is used, silicon as the carrier material for the chip 10 has an absorption of approximately 5%. 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, shown schematically in FIG. 1, with the result that there is a relatively low heating and thus low thermal stress on the chip 10 and the surfaces 15 of the chip 10 for the thermal connection to the conductor tracks 18 The connection temperature required for the circuit board 11 is essentially only achieved in the region 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 bump surface in the molten state of the bumps 16 , which often lead to a hy perboloid-shaped formation of the bumps during the remelting process, an associated self-aligning effect (self-aligning) 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 must 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 circuit board 27 has a transparent carrier material, for example FR4, so that the laser radiation 12 emitted from the end cross section 22 of the optical fiber 13 can get into the connection plane 23 between the circuit board 27 and the polyester film 25 without substantial absorption, in order to be analog there to be absorbed to the embodiment shown in Fig. 1 in here on the pads 26 of the plate 27 bumps 29 formed substantially.

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 (9)

1. A method for the thermal connection of two contact elements arranged on a respective substrate by means of a connecting material, the substrates being arranged to carry out the connection such that the contact elements overlap in a connecting plane and to achieve the necessary connecting temperature in the connecting plane a substrate of its the contact elements on the opposite side are exposed to energy, characterized in that radiation energy is applied, the transparency of the substrate ( 10 , 27 ) and the wavelength of the radiation ( 12 ) being matched to one another such that the radiation ( 12 ) is essentially passed through the substrate ( 10 , 27 ) and absorbed in the region of the connection plane ( 23 ) between the substrates ( 10 , 11 ; 27 , 25 ). 2. The method according to claim 1, characterized in that the connecting material has a degree of absorption matched to the wavelength of the radiation ( 12 ). 3. The method according to claim 1, characterized in that the connecting material has an absorption coating with a to the wavelength of the radiation ( 12 ) abge tuned degree of absorption. 4. The method according to one or more of the preceding claims, characterized in that a reflection coating for reflecting the radiation in the connection plane ( 23 ) is provided at least on the surface facing the connection plane ( 23 ) facing away from the radiation source arranged substrate. 5. Method according to one or more of the preceding Expectations, characterized, that a laser source is used as the radiation source. 6. A device for producing a thermal connection between two contact elements according to one or more of the preceding claims, characterized by a radiation source for emitting radiation ( 12 ) with a defined wavelength, which is arranged on the back of the substrate ( 10 , 27 ) through which the radiation for absorption in the connection level between the substrates ( 10 , 11 ; 27 , 25 ) is transmitted. 7. The device according to claim 6, characterized in that the radiation source is designed as a laser source in a laser arrangement with at least one optical fiber ( 13 ) having light guide means for transmitting the laser radiation ( 12 ) to the back ( 14 ; 28 ) of the substrate ( 10 ; 27 ). 8. The device according to claim 7, characterized, that the light guide means multiple optical fibers has, in terms of their number, arrangement and of its outlet cross-section for connection with mutually determined pairings of contact elements ent speak.   9. Apparatus according to claim 7, characterized in that the laser arrangement is provided with a focusing device for focusing the laser radiation (12) into the connecting plane (23) or a focal plane at a predetermined distance to the connecting plane (23).