Circuit board structure and method for manufacturing a circuit board structure

Abstract

The present publication discloses a circuit-board structure, including a conductor layer on an insulating material layer, and a conductor pattern on top of the conductor foil. A component is attached to the conductor foil and the conductor pattern, the component embedded at least in part in adhesive which attaches the component to the insulating material layer. A recess is formed in the conductor foil and the insulating material layer, and contact openings are in the insulating material layer at locations of contact areas of the component. Conductor material of the conductor foil is not present outside the conductor pattern, and the conductor foil is located between the conductor pattern and the insulating material layer.

Claims

1. A circuit-board structure comprising: a conductor foil on an insulating material layer; a conductor pattern on top of the conductor foil; a component attached to the conductor foil and the conductor pattern, the component embedded at least in part in adhesive which attaches the component to the insulating material layer; a recess formed in the conductor foil and the insulating material layer; and contact openings in the insulating material layer at locations of contact areas of the component, wherein conductor material of the conductor foil is not present outside the conductor pattern, and wherein the conductor foil is located between the conductor pattern and the insulating material layer.

2. The circuit-board structure of claim 1, wherein the conductor pattern is on top of the conductor foil in openings of a conductor-pattern mask formed by a patterned insulating layer spread on the conductor foil.

3. The circuit-board structure of claim 2, wherein the patterned insulating layer is a resist layer.

4. The circuit-board structure of claim 2, wherein the patterned insulating layer is a photoresist layer.

5. The circuit-board structure of claim 1, further comprising a layer of a metal or metal alloy on a surface of the conductor pattern or on an interface between the conductor foil and the conductor pattern.

6. The circuit-board structure of claim 1, wherein the contact openings are through the conductor pattern and the conductor foil.

7. The circuit-board structure of claim 1, wherein the contact openings are through the conductor foil.

8. The circuit-board structure of claim 7, wherein the contact openings are through the conductor pattern.

9. The circuit-board structure of claim 8, wherein the contact openings in the conductor pattern correspond to the contact openings in the insulating material layer and the conductor foil.

10. The circuit-board structure of claim 1, further comprising adhesive which attaches the component to the conductor foil and the conductor pattern.

11. The circuit-board structure of claim 10, wherein the adhesive which attaches the component to the conductor foil and the conductor pattern completely fills a space between the component and portions of the conductor foil and the conductor pattern not in contact with the component.

12. The circuit-board structure of claim 1, further comprising a filler material which fills the recess.

13. The circuit-board structure of claim 1, further comprising an insulator layer which surrounds the component and supports the conductor pattern.

14. The circuit-board structure of claim 13, wherein the insulator layer which surrounds the component comprises a sheet of insulating material with an opening at a location of the component.

15. The circuit-board structure of claim 2, wherein the conductor pattern was grown on top of the conductor foil.

16. The circuit-board structure of claim 1, wherein the component is located between the conductor pattern and a second conductor pattern.

17. The circuit-board structure of claim 1, wherein the adhesive is a thermally cured epoxy.

Description

(1) In the following, the invention is examined with the aid of examples and with reference to the accompanying drawings.

(2) FIGS. 1-8 show a series of cross-sections of the intermediate stages of the circuit-board structures, in a manufacturing process according to a first embodiment.

(3) FIGS. 9-16 show a series of cross-sections of the intermediate stages of the circuit-board structures, in a manufacturing process according to a second embodiment.

(4) FIGS. 17-22 show a series of cross-sections of the intermediate stages of the circuit-board structures, in a manufacturing process according to a third embodiment.

(5) FIGS. 23-26 show a series of cross-sections of the intermediate stages of the circuit-board structures, in a manufacturing process according to a fourth embodiment.

(6) FIGS. 27-32 show a series of cross-sections of the intermediate stages of the circuit-board structures, in a manufacturing process according to a fifth embodiment.

(7) In the first example, the circuit-board blank shown in FIG. 1 is manufactured first of all. The circuit-board blank of FIG. 1 comprises an insulating-material layer 1, a conductor foil 3 on the first surface of this, and a conductor foil 2 on the second surface.

(8) The circuit-board blank also comprises a recess 4. In addition, the circuit-board blank comprises a thinner insulating-material layer 11 between the insulating-material layer 1 and the conductor foil 2. The insulating-material layer 11 can be of material differing from that of the insulating-material layer 1, or it can be part of the insulating-material layer 1. In the former case, the circuit-board blank of FIG. 1 may have been formed, for example, by laminating together or otherwise combining with each other the insulating-material layer 1, the conductor foil 2, the conductor foil 3, and the insulating-material layer 11. In the latter case, the circuit-board blank of FIG. 1 may have been formed, for example, in such a way that a recess 4 has been made in the blank formed by the insulating-material 1, the conductor foil 2, and the conductor foil 3. In that case, the recess 4 will not extent completely through the insulating-material layer 1, but instead a corresponding part of the insulating-material layer 11 has been left on the ‘bottom’ of the recess.

(9) The method of the example can, of course, be modified in such a way that the recess 4 extends to the conductor foil 2, in which case there will not be an insulating-material layer 11 in the circuit-board blank, at least at the location of the recess. However, at least in some embodiments the reliability of the circuit-board structure can be improved by using an insulating-material layer 11. This is due to the fact that the use of an insulating-material layer 11 for its part ensures that unnecessary openings will not remain in the insulating material between the component and the conductor foil 2.

(10) Manufacture continues from the situation shown in FIG. 1, by spreading resist layers 5, typically photoresist layers, on the surfaces of the conductor foils 2 and 3. This stage is shown in FIG. 2. The photoresist layers 5 are exposed through a patterned mask and after this the blank is developed. After developing, the exposed photoresist layers 5 are patterned in the desired manner to form conductor-pattern masks, which is shown in FIG. 3.

(11) Manufacture is continued by electrolytically growing a conductor material, typically copper, in the areas from which the photoresist was removed. The desired conductor patterns 6 and 7 are then formed on the surfaces of the conductor foils 2 and 3, which is shown in FIG. 4. The thickness of the conductor pattern can be, for example, 20 micrometres while the width of the line of the conductor patterns being made can be less than 20 micrometres. The method can thus also be used to manufacture small and precise conductor patterns.

(12) The method can be modified in such a way that a layer of some other metal or metal alloy, for example tin, can be made on the surface of the conductor patterns 6 and 7, or on the interface between the conductor foils 2 and 3 and the conductor patterns 6 and 7.

(13) This layer can be used as an etching stop.

(14) The method can also be modified in such a way that the recess 4 is made only after the spreading of the photoresist layer 5, or at an even later process stage.

(15) After the manufacture of the conductor patterns 6 and 7, the resist layers 5 can be removed. In addition, contact openings 8 are made in the conductor pattern 6 of the circuit-board blank, at the locations of the contact areas of the component. The contact openings 8 can be made in such a way that they essentially extend through the conductor pattern 8, or in such a way that they essentially extend through both the conductor pattern 8 and the conductor foil 2, (i.e. through the entire conductor layer). It is also possible to make the contact openings from the other direction, in such a way that they extend through only the insulating-material layer 11 and the conductor foil 2. In the example, the contact openings 8 are made in such a way that they extend through the conductor pattern 6, the conductor foil 2, and the insulating-material layer 11. FIG. 4 shows the circuit-board blank after this intermediate stage.

(16) The contact openings 8 can be made, for example, by drilling with a laser. The contact openings 8 are aligned correctly in position relative to the conductor pattern 6. The mutual position of the contact openings 8 corresponds to the mutual position of the contact areas of the component. Thus, at least one contact opening 8 is made for each contact area participating in the creation of an electrical contact. The surface area of the contact openings 8 being made can be more or less as large as the surface area of the corresponding contact areas. The surface area of a contact opening 8 can, of course, also be selected to be smaller, or in some embodiments slightly larger, than the surface area of the corresponding contact area.

(17) In the example, the component 9 is attached to the circuit-board blank with the aid of an adhesive 10. For the gluing, an adhesive layer 10 is spread on the surface of the insulating-material layer 11, on the ‘bottom’ of the recess 4. FIG. 5 shows this intermediate stage. Alternatively, the adhesive layer can be spread on the attachment surface of the component 9, or on both the attachment surface of the component 9 and on the surface of the insulating-material layer 11. The adhesive 10 can also be spread in stages and in layers. After this, the components 9 can be aligned in the positions designed for the components 9, with the aid of alignment marks. For example, the contact openings 8, or the conductor patterns 6 or 7, or separate alignment marks (not shown in the figures) can act as alignment marks. FIG. 6 shows the circuit-board blank after the gluing of the component 9.

(18) The term attachment surface of the component 9 refers to that surface of the component 9 that will face the conductor pattern 6. The attachment surface of the component 9 comprises contact areas, by means of which an electrical contact can be made to the component. The contact areas can be, for example, flat areas on the surface of the component 9, or more usually contact protrusions, such as contact bumps, on the surface of the component 9. There are usually at least two contact areas or contact protrusions in the component 9. In complex microcircuits there can well be many contact areas.

(19) In many embodiments, it is advantageous to spread so much adhesive on the attachment surface or attachment surfaces that the adhesive completely fills the space between the component 9 and the structure coming against the component. A separate filler agent will then not be required. Good filling will reinforce the mechanical connection between the component 9 and the circuit-board blank, so that a mechanically more durable construction will be achieved. A comprehensive adhesive layer 10 without gaps will also support the conductor pattern and protect the structure in later process stages. During gluing, adhesive also usually gets into the contact openings 8, if these open towards the attachment surface.

(20) The term adhesive refers to a material, by means of which a component can be attached to the circuit-board blank. One property of an adhesive is that the adhesive can be spread on the surface of the circuit-board blank and/or of the component in a relatively fluid form, or otherwise in a form that conforms to surface shapes, for example, in the form of a film. Another property of an adhesive is that after spreading the adhesive hardens or can be hardened, at least partly, so that the adhesive will be able to hold the component in place at least until the component is attached to the structure in some other way. The third property of the adhesive is its adhesive ability, i.e. its ability to bond to the surface being glued.

(21) The term gluing refers to attaching the component and the circuit-board to each other with the aid of an adhesive. In gluing, adhesive is thus brought between the component and the circuit-board blank and the component is set in a suitable position relative to the circuit-board blank, in which the adhesive is in contact with the component and the circuit-board blank and at least partly fills the space between the component and the circuit-board blank. After this, the adhesive is allowed to (at least partly) harden or the adhesive is (at least partly) actively hardened, so that the component attaches to the circuit-board blank with the aid of the adhesive. In some embodiments, the contact protrusions of the component may, during gluing, extend through the adhesive layer to come in contact with the rest of the structure of the circuit-board blank.

(22) The adhesive used in the embodiments is, for example, a thermally cured epoxy. The adhesive is selected in such a way that the adhesive used has sufficient adhesion with the circuit-board blank and the component. One advantageous property of the adhesive is a suitable coefficient of thermal expansion, so that the thermal expansion of the adhesive will not differ too much from the thermal expansion of the surrounding material during the process. The adhesive selected should also preferably have a short hardening time, preferably of a few seconds at most. In this time the adhesive should harden at least partly in such a way that it is able to hold the component in place. The final hardening can take clearly more time and the final hardening can indeed be designed to take place in connection with later process stages. The electrical conductivity of the adhesive is preferably in the order of the electrical conductivity of insulating materials.

(23) The component 9 to be attached can be, for example, an integrated circuit, such as a memory chip, a processor, or an ASIC. The component to be attached can also be, for example, a MEMS, LED, or a passive component. The component to be attached can be cased or uncased, and it can comprise contact bumps in the contact areas or be without bumps. There can also be a conductor surfacing thinner than a contact bump on the surface of the contact areas of the component. The outer surface of the contact areas of the component can thus be on the level of the outer surface of the component, on the bottom of recesses on the surface of the component, or on the surface of protrusions extending from the surface of the component.

(24) After the gluing of the component 9, the recess is filled with a filler material 12. The example can also be modified in such a way that manufacture is started from a circuit-board blank (the situation in FIG. 1), which comprises only a conductor foil 2 and possibly an insulating-material layer 11. After this, process stages that are otherwise the same as those described above, except that naturally the method stages relating to the conductor foil 3, the conductor pattern 7, and the resist layer 5 relating to them are omitted. In this embodiment, the circuit-board blank comprises, after the gluing of the component (refer to FIG. 6): a conductor layer formed by a conductor foil 2 and a conductor pattern 6, an adhesive layer 10, optionally an insulating-material layer 11 between the conductor layer and the adhesive layer 10, contact openings 8, and at least one component 9.

(25) In this modified embodiment, there is not recess 4 to be filled, instead in this stage an insulator layer1, which surrounds the component 9 and supports the conductor layers 2 and 6, is made on the surface with the component 9 of the circuit-board blank. The insulator layer 1 can be formed, for example, by putting an insulating-material sheet, in which openings have been made at the location of the components 9, on top on the circuit-board blank. In addition, a unified insulating-material sheet can be put on top of the insulating-material sheet 9. Both sheets can be similar, or sheets than differ from each other can also be used, at least one of which is prehardened or unhardened. Examples of materials suitable for the insulator layer 1 are PT (polyimide), FR4, FR5, aramid, polytetrafluoroethylene, Teflon®, LCP (liquid crystal polymer), and a prehardened binder layer, i.e. prepreg. The insulating-material sheets put on top of the circuit-board blank are pressed, with the aid of heat and pressure, to form a unified insulator layer 1. In the insulating-material sheets, on the upper surface of one can also be a ready conductor-pattern layer, so that after pressing the circuit-board blank comprises at least two conductor-pattern layers, as shown by the series of figures. In this embodiment, conductor patterns 7 can, however, also be designed at the location of the components 9.

(26) Both in the example shown in the figure series and in the above described modification, it is next possible to make vias 13, with the aid of which electrical contacts are made between the contact areas of the components 9 and the conductor patterns 6. For the making of vias, the contact openings 8 are cleaned of adhesive and other materials that may have been pushed into them. In connection with the cleaning of the contact openings 8, it is also possible to clean the contact areas of the components 9, thus further improving the preconditions for making a high-quality electrical contact. The cleaning can be performed using, for example, a plasma technique, chemically, or with the aid of a laser. If the contact openings 4 and the contact areas are already sufficiently clean, the cleaning can naturally be omitted.

(27) If the contact openings 8 were made to only partly penetrate, the contact openings 8 are opened in this stage. It is also possible to proceed in such a way that the contact openings 8 are made entirely in this stage.

(28) After cleaning, it is also possible to examine the success of the alignment of the component 9, as the contact areas of a correctly aligned component will be visible through the contact openings 8, when viewed from the direction of the conductor pattern.

(29) After this, a conductor material is introduced to the contact openings 8, in such a way that it forms an electrical contact between the component 9 and the conductor pattern 6. The conductor material of the vias 13 can be made, for example, by filling the contact openings 8 with an electrically conductive paste. The conductor material can also be made using one of several growing methods known in the circuit-board industry. High-quality electrical contacts can be made, for example, by forming a metallurgical connection by growing a conductor material using a surfacing method, for example, a chemical or electrochemical method. One good alternative is the growing of a thin layer using a chemical method and continuing the growing using a more economical electrochemical method. The term filling refers to the fact that the contact openings are at least substantially filled with the conductor material. Instead of filling, surfacing can also be performed in such a way that only the edges of the contact openings are surfaced. In addition to these methods, it is of course possible to also use some other method, which will be beneficial in terms of the end result.

(30) In the example of the figure series, the contact openings 8, the contact areas of the component 9, and the conductor patterns 6 are surfaced first of all with a thin conductor layer and then afterwards the thickness of the conductor layer is increased electrolytically until the contact openings 8 are filled with conductor material. FIG. 7 shows the structure after the growing. After this, the circuit-board blank is etched, to remove the excess conductor material. If a protective membrane is used on the surface of the conductor patterns 6 and 7, the conductor material is removed essentially only from those parts of the conductor foils 2 and 3 that remain outside the conductor patterns 6 and 7. Alternatively, it is possible to etch the entire conductor layer, so that the material of the conductor foils 2 and 3 is removed from outside the conductor patterns 6 and 7. In that case, material of the conductor patterns 6 and 7 too will be removed, but the conductor patterns 6 and 7 will be copied into the material of the conductor foils 2 and 3.

(31) The series of FIGS. 9-16 shows one variation of the examples described above. In the variation, the suitable parts of the method stages described above are utilized and the procedure is as follows: A circuit-board blank is made, which comprises an insulator layer 1, a recess 4, and conductor foils 2 and 3 (FIG. 9). Photoresists 5 are spread and exposure takes place through the masks (FIG. 10). The exposed areas 5′ are shown darkened in the figure. Contact openings 8 are made (FIG. 11). Adhesive 10 is spread (FIG. 12). The component 9 is attached to the circuit-board blank with the aid of an adhesive layer 10 (FIG. 13) and the recess 4 is filled with a filler agent 12. The resist is developed, so that all that remains are the unexposed areas of the resist 5. The contact openings 8 are cleaned. The circuit-board blank after these stages is shown in FIG. 14. Conductor material is grown using an electrolytic method. The conductor material then grows in the openings of the resist 5 and the contact openings 8 are filled, thus forming both conductor patterns 6 and 7 and vias 13 (FIG. 15). The resist 5 is removed and the conductor material is etched, so that the desired conductor pattern is separated from the conductor layer when the conductor material is removed from the areas between the conductor patterns (FIG. 16).

(32) In the embodiment shown in the series of FIGS. 9-16 the conductor foils 2 and 3 are preferably thin relative to the conductor patterns 6 and 7 to be grown on their surfaces. The conductor foils 2 and 3 are thus intended to conduct the current required by the electrolytic growing to the growing areas. If the conductor foils 2 and 3 are thin relative to the conductor patterns 6 and 7, the etching of the conductor foils 2 and 3 away from outside the conductor patterns 6 and 7 will not substantially affect the relative dimensions of the conductor patterns 6 and 7.

(33) The series of FIGS. 17-22 shows a third variation of the examples described above. In the variation, suitable parts of the method stages described above are utilized and the procedure is as follows: A circuit-board blank is made, which comprises a conductor foil 2 and a conductor pattern 6 (FIG. 17). This can be made, for example, in such a way that a resist 5, which is exposed and developed, is spread on top of the conductor foil 2. After this, metal is grown in the openings formed in the resist 5, for example, using an electrochemical method. In this variation, contact openings are also defined in the exposure mask of the resist, so that the resist will remain at the locations of the contact openings 8′. Thus, in connection with the growing of the conductor pattern 6, contact openings 8 are also formed in the conductor patterns 6, and are thus aligned directly and in a self-aligning manner in the correct places relative to the conductor pattern 6. The resist is removed and the contact openings 8 are opened to also extend through the conductor foil 2 (FIG. 18). The component 9 is glued onto the surface of the conductor pattern 6 with the aid of an adhesive 10 (FIG. 19). The component is aligned in the correct position relative to the conductor pattern 6 and the contact openings 8. An insulating-material layer 1 is made on top of the circuit-board blank (FIG. 20). The contact openings 8 are cleaned and vias 13 are made in the contact openings from a conductor material (FIG. 21). In the example of the figure, the vias 13 are made using a surfacing method. In that case, the vias are surfaced in such a way that the necessary electrical contact arises, i.e. generally a conductor layer is made at least on the edges of the contact openings 8. In the example of the figure, the contact openings 8 are grown full of the conductor material. The more conductor material is put into a via 13, the better will be the conductivity of the via 13. The vias 13 are indeed preferably made to be at least substantially filled with conductor material. The conductor foil 2 is removed, for example, by etching (FIG. 22).

(34) The series of FIGS. 23-26 shown a fourth variation of the examples described above. In the variation, suitable parts of the method stages described above are utilized and the procedure is as follows: A circuit-board blank is made, which comprises a conductor foil 2 and a conductor pattern 6 (FIG. 23). This can be made, for example, in such a way that a resist 5, which is exposed and developed, is spread on top of the conductor foil 2. After this, metal is grown in the openings formed in the resist 5, for example, using an electrochemical method. A component 9 is glued on top of the conductor pattern 6, with the aid of an anisotropically conductive adhesive 20 (FIG. 24). The anisotropically conductive adhesive 20 forms an electrical contact in the direction between the contact areas of the component and the conductor pattern 6. The adhesive 20 is, however, electrically insulating in the transverse direction, so that an electrical contact is not formed between the contact areas of the component, nor between the separate conductors of the conductor pattern 6. An insulating-material layer 1 is made on top of the circuit-board blank and on the surface of that a conductor foil 3 (FIG. 25).

(35) The conductor foil 2 is removed, for example, by etching. The conductor foil 3 is patterned to form a conductor pattern 7 (FIG. 26).

(36) The series of FIGS. 27-32 shows a fifth variation of the examples described above. In the method, suitable parts of the method stages described above are utilized, and the procedure is as follows: A circuit-board blank is made, which comprises a conductor foil 2 and a conductor pattern 6 (FIG. 27). This can be made, for example, in such a way that a resist 5, which is exposed and developed, is spread onto top of the conductor foil 2. After this, metal is grown in the openings formed in the resist 5, for example, using an electrochemical method. A second resist 15, which is exposed and developed, is spread on top of the resist 5 and conductor pattern 6. A conductor material is made in the opening formed in the resist 15, for example, using an electrochemical method. The made conductor areas form contact bumps 17 on the surface of the conductor pattern 6 (FIG. 28). The resists 5 and 15 are removed (FIG. 29). A component 9 is attached on top of the conductor pattern 6 and against the contact bumps 17, using a suitable method (FIG. 30). In the example of the figure, the joint is made by an ultrasonic bonding method or alternatively by a thermo-compression bonding method. In the example of the figure, a component 9 is used, which does not itself contain contact bumps. An insulating-material layer 1 is made on top of the circuit-board blank, and a conductor foil 3 of top of that (FIG. 31). The conductor foil 2 is removed, for example, by etching. The conductor foil 3 is patterned to form a conductor pattern 7 (FIG. 32).

(37) In the embodiments, it is possible to also use a separate support layer to support the conductor foil, or the conductor layer formed by the conductor foil and the conductor pattern.

(38) A suitable intermediate layer, which will not dissolve in the etching agent used, or will dissolve in it extremely slowly, can also be used between the conductor foil and the conductor pattern, or on the surface of either of them. Thus the etching stops at the intermediate layer and the desired surface can be defined precisely. An intermediate layer of this kind can be made, for example, from some other metal, such as tin. If necessary, the intermediate layer can be removed, for example, chemically with some other etching agent.

(39) When using a manufacturing method, in which the contact openings 8 are aligned and made after the manufacture of the conductor pattern 6, the sensitivity of the method to alignment errors can be reduced by dimensioning the diameter of the contact openings 8 to be greater than the width of the conductors of the conductor pattern 6.

(40) There are numerous variations of the methods according to the examples presented above while the methods depicted by the examples can also be combined with each other. The variations can relate to individual process stages, or to the mutual sequence of the process stages.

(41) Many features, which do not appear in the previous examples, can also be manufactured into the circuit-board structure. For example, in addition to vias that participate in the creation of electrical contacts, thermal vias can also be made, which are intended to conduct heat more efficiently away from the component 9. The increase in the efficiency of heat conducting is based on the thermal conductivity of the thermal via being greater than that of the insulating material surrounding the component. As electrical conductors are typically also good thermal conductors, the thermal vias can in most cases be made using the same technique and even in the same process stage as the electrical contacts to the components 9.

(42) On the basis of the previous examples, it is obvious that the method can also be used for manufacturing many different kinds of three-dimensional circuit structures. The method can be used, for example, in such a way that several components, for example, semiconductor chips, are placed on top of each other, thus forming a packet containing several components, in which the components are connected to each other to form a single functional totality. Such a packet can be termed a three-dimensional multi-chip module.

(43) The examples of the figures depict some possible processes, with the aid of which our invention can be exploited. However, our invention is not restricted to only the processes described above, but instead the invention covers various other processes too and their end products, within the full scope of the Claims and taking equivalence interpretation into account. The invention is also not restricted to only the structures and methods described by the examples, but instead it will be obvious to one versed in the art that various applications of our invention can be used to manufacture very many different kinds of electronic modules and circuit boards, which may even differ greatly from the examples presented. Thus the components and circuits of the figures are presented only with the intention of illustrating the manufacturing process. Many alterations can be made to the processes of the examples described above, while nevertheless not deviating from the basic idea according to the invention. The alterations can related, for example, to the manufacturing techniques depicted in the various stages, or to the mutual sequence of the process stages.

(44) With the aid of the invention, it is also possible to manufacture component packets for attachment to a circuit board. Such packets can also contain several components, which are connected electrically to each other.

(45) The method can also be used to manufacture entire electrical modules. The module can also be a circuit board, to the outer surface of which components can be attached, in the same way as to a conventional circuit board.