CN114787417A

CN114787417A - Method for producing an electrically conductive structure

Info

Publication number: CN114787417A
Application number: CN202080085464.0A
Authority: CN
Inventors: B.罗森纳; R.A.克鲁格; A.费舍尔
Original assignee: LPKF Laser and Electronics AG
Current assignee: LPKF Laser and Electronics AG
Priority date: 2019-12-11
Filing date: 2020-10-01
Publication date: 2022-07-22
Also published as: JP2023505869A; EP4073286A1; KR20220087531A; DE102019133955A1; US20230026070A1; WO2021115518A1; DE102019133955B4

Abstract

The invention relates to a method for producing a composite structure made of at least one electrically conductive structure, a carrier made of a non-conductive carrier material from a thermosetting plastic, and at least one electronic component, wherein the non-conductive carrier material contains an additive having catalytically active species formed in a metallization bath without an external current as a result of the action of laser radiation. By using pulsed laser radiation, a quasi non-thermal treatment of the carrier material is achieved in that the material directly evaporates due to the very high peak intensity, so that no or hardly any melt is produced.

Description

Method for producing an electrically conductive structure

The invention relates to a method for producing a composite structure by means of laser radiation, said composite structure being produced from at least one electrically conductive structure, a carrier and at least one electronic component, said carrier being produced from a non-conductive carrier material of plastic origin, said non-conductive carrier material containing an additive which subsequently forms a catalytically active substance by irradiation with laser radiation in a metallization bath without an external current.

In a process known as Laser-direct structuring (LDS), the carrier material is injection molded into a molded part in a single-component injection molding process using plastic granules with special additives. By means of a laser, the additive can be converted in a site-selective manner into catalytically active crystal nuclei in a physicochemical reaction in which the metal is deposited in the subsequent chemical metallization bath at the sites treated in this way.

DE 10132092 a1 describes a circuit structure on a non-conductive carrier material, which consists of metal nuclei and a metallization subsequently applied to the metal nuclei, the metal nuclei being generated by decomposition of a non-conductive inorganic metal compound contained in the carrier material in a finely distributed manner by means of electromagnetic radiation.

DE 102014114986 a1 describes a method for producing a circuit structure, in which selective laser irradiation is carried out on a circuit carrier in accordance with the circuit structure to be produced, and the circuit structure is then produced in a metallization bath without an external current. Here, for example, laser radiation having a wavelength of 1,064 nm and a pulse frequency of 100kHz is used.

In the method disclosed in DE 102013100016 a1 for producing such an electrically conductive structure, a thermoplastic copper oxide-polyester mixture is mixed into a carrier material and injection molded into a workpiece, which is then selectively activated for subsequent metallization by means of a laser.

Due to technical limitations, it is now possible to reliably manufacture line widths of a minimum of 150 μm by means of an LDS process. To further advance the desired MID miniaturization, this limitation must be further suppressed. For this purpose, efforts are being made to further focus the laser radiation and to direct it more precisely onto the surface of the shaped part.

DE 102012010635 a1 relates to a method for the direct 3D structuring of hard, brittle optical materials, in which the surface is structured with ultrashort pulsed lasers and the 3D structure or shape is thereby introduced in a targeted manner.

The occurrence of foreign deposits has proven to be a disadvantage in practice in the implementation of processes for producing electrically conductive structures on/in non-conductive carrier materials, for example by laser activation in the case of wires, in particular in the case of thermosets as carrier materials. Since the thermosetting plastic does not melt but decomposes, a large amount of carbon is released, which is catalytically active in the electroless metallisation bath.

In the subsequent metallization of the metal atoms, extraneous deposits also appear in an undesirable manner outside the processing region on catalytically active corrosion products in the metallization bath. Such foreign deposits can actually cause a short circuit if the distance between the resulting lines is small. Here, the degradation products also prove to be very problematic, since, owing to their high temperature during decomposition, they can bond again to the plastic surface outside the structured region and can therefore hardly be removed anymore. As the structures to be produced become more and more compact, these problems occur not only in thermosetting plastics but in principle in all plastics.

If the temperature is too high during structuring, the exfoliation products become so hot that they adhere strongly to the surface of the carrier material that it can no longer be cleaned reliably. The adhering, catalytically active peeling products can lead to "beading" in particular in the region of the recesses due to foreign deposits in the edge regions of the recesses. Although practice has shown that this effect can be minimized by significantly reducing the laser power, this results in significantly longer cycle times.

The object of the present invention is therefore to provide a method in which the damage to the electrically conductive structures produced in this way on a carrier material as a result of the ablation products is significantly reduced. According to the invention, in particular, a further reduction in the structural size of the electrically conductive structure should be enabled.

According to the invention, this object is achieved by a method according to the features of claim 1. Further embodiments of the invention can be found in the dependent claims.

In the method according to the invention for producing a composite structure by means of laser radiation, the composite structure being made of at least one electrically conductive structure, a carrier and at least one electronic component, the carrier being made of an electrically non-conductive carrier material from a thermosetting plastic, wherein the electrically non-conductive carrier material contains an additive which subsequently forms a catalytically active substance by irradiation with laser radiation in an electroless metallisation bath, the electrically conductive structure being formed by irradiation with pulsed laser radiation having a pulse duration of less than 100 picoseconds and subsequent electroless metallisation, and the pulse repetition rate being set such that, on the respective additive or additive region to be activated, successive pulses are deflected onto the additive or additive region one above the other.

The present invention is based on the unexpected recognition that: the method for producing electrically conductive structures by laser activation of metal compounds contained in additives, in particular with ultrashort pulsed lasers, can be used without problems, in particular in thermosetting plastics, and has the advantage here that fewer foreign deposits occur.

For the first time, a method for laser direct structuring is proposed which on the one hand reliably achieves the energy input required for laser activation, but on the other hand limits the heating such that not only significantly fewer ablation products are produced, but also the temperature of the ablation products is so low that the adhesion to the carrier material is very low and can therefore be easily removed.

According to the invention, particularly fine electrically conductive structures can be produced in this way, since the short-circuit risk associated therewith is also prevented by avoiding foreign deposits. Thereby the width of the structures and the distance between the structures can be reduced.

A further highly effective embodiment of the method according to the invention is also achieved in that the number of laser pulses per second (pulse repetition rate) is designed to be so large, for example 2 to 2.5MHz, that successive pulses act with regions of action that overlap one another on the respective additive particles or additive regions to be activated. In this way, a plurality of successive pulses are always applied to each additive particle or each additive region, so that the energy input is correspondingly increased.

This enables precise temperature management, by means of which the following are excluded: the thermal energy coupled into the support material is so low that the temperature is not sufficient to reduce the additives, such as Cu — Cr spinel, to elemental copper, and therefore catalytically active species for the desired metallization are not or cannot be reliably generated, and irregular partial metallizations occur in particular. Furthermore, the overlapping regions of action of the successive pulses also ensure that the temperature during structuring is not too high, so that the flaking products do not heat up compared to the prior art and thus do not adhere to the carrier material in an undesirable manner, so that they cannot be removed again reliably.

By means of this method, a composite structure is produced in which a non-conductive support material contains an additive with catalytically active species formed as a result of the action of laser radiation, wherein the electrically conductive structure is formed by irradiation with pulsed laser radiation, in particular ultrashort pulsed laser light, and by then metallization in a metallization bath. According to the invention, by using pulsed laser radiation, a quasi non-thermal treatment of the carrier material is achieved with the correct selection of the parameters in such a way that the material evaporates directly due to the very high peak intensity, so that no or almost no melt is produced. The pulses are so short that, during the pulse duration, no energy is transferred into the lattice oscillation and thus into the temperature increase. It is therefore believed that the energy introduced by the ultrashort pulse corresponds to the energy required for evaporation of the material, and therefore no other energy is used for thermalization.

Contrary to the above prejudice of the academia, the invention is based on the unexpected recognition that the activation of the metal compounds and the formation of catalytically active nuclei in those regions thus activated by laser light corresponds to a thermal process which requires high temperatures for the decomposition of the additive particles: not the heat energy input but the maximum strength forms the basis and thus creates the cause and necessary prerequisites for the activation of the metal compound.

It has proven particularly advantageous here for the electrically non-conductive support material to comprise at least one inorganic filler with a maximum particle size of 50 μm. Filler materials which are not destroyed or broken apart by the active laser radiation can thus also be used, since these filler materials, because of their small particle size, do not impair or hinder subsequent processing, for example the introduction of recesses such as holes, including through-holes or blind holes. The filler can therefore be selected without restriction according to the desired technical properties of the thermoset, for example with regard to viscosity, CTE (Coefficient of Thermal Expansion) or setting time.

The catalytically active exfoliation products, which in the prior art are particularly disadvantageous with regard to adhesion, are therefore reliably prevented from forming what is known as "beading" in the region of the pores. According to the invention, the cycle time is thus not increased. With ultrashort pulse lasers using picosecond laser sources, significantly less heat is generated upon ablation. This prevents the generation of hot spalling products and formation of a ledge during drilling, even at higher powers. The use of higher power leads to a higher ablation rate, whereby in practice even cycle times can be reduced.

In a particularly advantageous manner, the change from nanosecond pulse to picosecond pulse, with the other parameters remaining unchanged during structuring of the carrier material, and the correspondingly reduced heat input which can lead to inadequate activation of the additive, is compensated by the overlapping region of the individual pulses, which can be achieved by using higher pulse repetition rates, for example in the range between 2 and 2.5 MHz.

Another embodiment which is also very effective is also realized in the following way: the position and/or orientation of at least one electronic component in the carrier material is determined using a contactless measurement method, in particular using electromagnetic radiation, for example roentgen rays, the deviation of the actual position and/or the actual orientation from the target position and/or the target orientation is then determined, and correction values for the subsequent irradiation of the carrier material by means of pulsed laser radiation are derived therefrom, and finally the irradiation is carried out taking into account these correction values. Thereby, in particular when embedding one or more electronic components into the composite mass, the individual positional deviations of the electronic components from the target position are determined. For this purpose, the exact position and the degree of torsion of the electronic components are determined, for example, by means of the roentgen ray method, and the irradiation of the activatable additive or the catalytically active substance is carried out taking into account the correction values. The lines and holes to be structured can be adapted to the actual position and orientation of the electronic components in the carrier material by means of software, thereby avoiding rejects and significantly increasing the reliability.

When, according to a preferred embodiment, the size and/or mass of the individual filler particles contained in the carrier material is significantly greater than the size and/or mass of the individual additive particles contained in the carrier material, the size or mass difference of the filler particles on the one hand and the additive particles on the other hand results in an uneven distribution of the additive and filler particles in an unexpected manner, with the result that, during processing of the carrier material, the relatively large or heavy filler particles are predominantly collected in the inner or middle region of the carrier material, while the relatively small or light additive particles are displaced into the layers of the carrier material close to the edges, relative to this. By increasing the concentration of the additive in the layer close to the edge, the activation process can be significantly improved there, whereby the activation process can be carried out with a low radiation intensity without the total amount of additive added having to be increased for this purpose. At the same time, undesirable changes in the properties of the other materials are avoided by a corresponding reduction in the proportion of additives in the core part of the carrier material. For example, the LDS additive is contained in the support material in an amount of 3 to 15 weight percent, preferably 6 to 12 weight percent.

Claims

1. Method for producing a composite structure by means of laser radiation, the composite structure being made of at least one electrically conductive structure, a carrier and at least one electronic component, the carrier being made of an electrically non-conductive carrier material from a thermosetting plastic, wherein the electrically non-conductive carrier material contains an additive which subsequently forms catalytically active species by irradiation with laser radiation in an electrically current-free metallization bath, wherein the electrically conductive structure is formed by irradiation with pulsed laser radiation having a pulse duration of less than 100 picoseconds and subsequent electrically current-free metallization, and wherein the pulse repetition rate is set such that, in the region of the respective additive or additive region to be activated, pulses which follow one another are deflected onto the additive or additive region one above the other.

2. The method according to claim 1, characterized in that the laser radiation is imaged onto the non-conductive carrier material through a partially transmissive mask.

3. A method according to claim 1 or 2, characterized in that the laser radiation is positioned on the carrier using a polygon scanner.

4. Method according to at least one of the preceding claims, characterized in that a plurality of, in particular four, galvanometer scanners are used to position the laser radiation on the carrier.

5. Method according to at least one of the preceding claims, characterized in that the laser radiation is positioned on the carrier using a resonator mirror.

6. Method according to at least one of the preceding claims, characterized in that the actual position and/or the actual orientation of the electronic component in the carrier material is determined by using a contactless measurement method, in particular by means of roentgen rays, then the deviation of the actual position and/or the actual orientation from a target position and/or a target orientation is determined, and from this a correction value for the subsequent irradiation of the carrier material by means of the pulsed laser radiation is derived, and the irradiation is performed taking into account the correction value.