WO2024115586A1

WO2024115586A1 - Component carrier structure with cavity filled with flux material and solder ball embedded therein, apparatus and method to connect solder ball with component carrier structure

Info

Publication number: WO2024115586A1
Application number: PCT/EP2023/083585
Authority: WO
Inventors: Max Yang; Qijun LI; Eddick SUN
Original assignee: At&S Austria Technologie & Systemtechnik Aktiengesellschaft
Priority date: 2022-12-01
Filing date: 2023-11-29
Publication date: 2024-06-06
Also published as: CN118136607A

Abstract

Component carrier structure (100) which comprises a stack (102) comprising at least one electrically conductive layer structure (104) and at least one electrically insulating layer structure (106), at least one cavity (108), opening on one of external surfaces (110) of the component carrier structure (100), and flux material (112), at least partially filling said at least one cavity (108), wherein at least one solder ball (114) is provided, said at least one solder ball (114) being at least partially embedded in said at least one cavity (108) and said flux material (112).

Description

COMPONENT CARRIER STRUCTURE WITH CAVITY FILLED WITH FLUX MATERIAL AND SOLDER BALL EMBEDDED THEREIN, APPARATUS AND METHOD TO CONNECT SOLDER BALL WITH COMPONENT CARRIER STRUCTURE

The invention relates to a component carrier structure, an apparatus to connect at least one solder ball with a component carrier structure, and a method of connecting at least one solder ball with a component carrier structure.

In the context of growing product functionalities of component carriers equipped with one or more electronic components and increasing miniaturization of such electronic components as well as a rising number of electronic components to be mounted on the component carriers such as printed circuit boards, increasingly more powerful array-like components or packages having several electronic components are being employed, which have a plurality of contacts or connections, with ever smaller spacing between these contacts. Removal of heat generated by such electronic components and the component carrier itself during operation becomes an increasing issue. At the same time, component carriers shall be mechanically robust and electrically reliable so as to be operable even under harsh conditions.

When electrically connecting a component carrier, it may be desired but difficult to obtain a well-defined solder ball on the component carrier.

It is an object of the invention to allow manufacture of a component carrier with well-defined solder ball thereon.

In order to achieve the object defined above, a component carrier structure, an apparatus to connect at least one solder ball with a component carrier structure, and a method of connecting at least one solder ball with a component carrier structure according to the independent claims are provided.

According to an exemplary embodiment of the invention, a component carrier structure is provided which comprises a stack comprising at least one electrically conductive layer structure and at least one electrically insulating layer structure, at least one cavity opening on one of external surfaces of the component carrier structure, and flux material, at least partially filling said at least one cavity, wherein at least one solder ball is provided, said at least one solder ball being at least partially embedded in said at least one cavity and said flux material.

According to another exemplary embodiment of the invention, an apparatus to connect at least one solder ball with a component carrier structure is provided, the component carrier structure comprising a stack comprising at least one electrically conductive layer structure and at least one electrically insulating layer structure, at least one cavity opening on one of external surfaces of the component carrier structure, and flux material at least partially filling said cavity, said apparatus comprising a ball placement stencil comprising at least one ball passage, and being configured to allow the at least one solder ball to fall toward the at least one cavity and the flux material when said at least one ball passage is at least partially vertically aligned with the respective cavity, wherein the apparatus is configured so that when the stencil is in its working position with respect to the component carrier structure, the at least one solder ball is pushed to be entirely at or below an upper surface of the stencil, wherein a distance (see for example reference signs B3+B4 in Figure 1 and Figure 4) between said upper surface of the stencil and the respective external surface of the component carrier structure is lower than a diameter (see for example reference sign Bl in Figure 1 and Figure 4) of the at least one solder ball, so that the at least one solder ball is at least partially embedded in said at least one cavity and said flux material.

According to still another exemplary embodiment of the invention, a method of connecting at least one solder ball with a component carrier structure is provided, the method comprising providing the component carrier structure comprising a stack comprising at least one electrically conductive layer structure and at least one electrically insulating layer structure, at least one cavity opening on one of external surfaces of the component carrier structure, and flux material at least partially filling said at least one cavity, operating a ball placement stencil comprising at least one ball passage for allowing the at least one solder ball to fall toward the at least one cavity and the flux material when said at least one ball passage is at least partially vertically aligned with the respective cavity, pushing the at least one solder ball to be entirely at or below an upper surface of the stencil when the stencil is in its working position with respect to the component carrier structure, and adjusting a distance (see for example reference signs B3+B4 in Figure 1 and Figure 4) between said upper surface of the stencil and the respective external surface of the component carrier structure to be lower than a diameter (see for example reference sign Bl in Figure 1 and Figure 4) of the at least one solder ball, so that the at least one solder ball is at least partially embedded in said at least one cavity and said flux material.

In the context of the present application, the term "component carrier structure" may particularly denote a physical structure comprising one or a plurality of component carriers, or preforms thereof. For example, a component carrier structure may be a component carrier itself. It is also possible that a component carrier structure comprises a plurality of component carriers, for instance an array of component carriers or a panel comprising component carriers. Furthermore, it is also possible that a component carrier structure is a structure obtained during manufacturing component carriers, for example a panel or an array comprising a plurality of preforms of component carriers which may still be integrally connected. In particular, the component carrier structure may be configured as panel, array, pre-form of component carrier, or readily manufactured component carrier, in particular a printed circuit board or an integrated circuit substrate.

In the context of the present application, the term "component carrier" may particularly denote any support structure which is capable of accommodating one or more components thereon and/or therein for providing mechanical support and/or electrical connectivity. In other words, a component carrier may be configured as a mechanical and/or electronic carrier for components. In particular, a component carrier may be one of a printed circuit board, an organic interposer, and an IC (integrated circuit) substrate. A component carrier may also be a hybrid board combining different ones of the above mentioned types of component carriers.

In the context of the present application, the term "stack" may particularly denote a sequence of two or more layer structures formed on top of each other. For instance, layer structures of a layer stack may be connected by lamination, i.e. the application of heat and/or pressure. In the context of the present application, the term "layer structure" may particularly denote a continuous layer, a patterned layer, or a plurality of non- consecutive islands within a common plane.

In the context of the present application, the term "cavity" may particularly denote a blind hole or an opening in the component carrier structure, and in particular in a solder resist on top thereof, shaped and dimensioned for accommodating flux and a solder ball at least partially therein. A circumferential edge delimiting an exterior of the cavity at an interface between cavity and exterior surface of component carrier structure may be circular.

In the context of the present application, the term "external surface" or "main surface" of a body may particularly denote one of two largest opposing surfaces of the body. The external or main surfaces may be connected by circumferential side walls. The thickness of a stack, or another body having two opposing external or main surfaces, may be defined by the distance between the two opposing external or main surfaces.

In the context of the present application, the term "flux material" may particularly denote an agent fulfilling a certain function during assembly and/or soldering of a solder ball placed in and/or on a cavity. For instance, such an agent may be a chemical cleaning agent, a flowing agent and/or a purifying agent. In terms of soldering, the flux material may remove oxidized metal from the surfaces to be soldered, may seal out air thus preventing further oxidation, and/or may facilitate amalgamation by enhancing wetting characteristics of solder. Preferably, the flux material may be an electrically conductive material or an electrically insulating material. For instance, a composition of the flux material may be resin (for instance in a range from 30 to 40 weight percent, in relation to the entire weight of the flux material), Diethylene glycol monohexyl ether (for instance in a range from 20 to 30 weight percent, in relation to the entire weight of the flux material), activating agent (for instance in a range from 30 to 40 weight percent, in relation to the entire weight of the flux material), and a thixotropic agent (for instance in a range from 1 to 10 weight percent, in relation to the entire weight of the flux material), wherein a sum of all ingredients of the flux material will always be 100 weight percent. In the context of the present application, the term "solder ball" may particularly denote a round body of solderable material (for instance comprising tin or a solderable alloy). Such a solder ball may also be denoted as a solder bump. A solder ball may be a spherical or substantially spherical body. The solder ball may be placed in a component carrier structure's cavity filled at least partially with flux material and can then accomplish a connection (in particular an electrically conductive connection) between the component carrier structure and another electronic device (for instance a surface mounted electronic component, such as a semiconductor chip) by soldering. Thus, a solder ball may be a ball of solder that provides a contact between the component carrier structure (for example a metallic pad thereof) and another electronic device (such as a chip package or a multichip module).

In the context of the present application, the term "solder ball at least partially embedded in cavity and flux material" may particularly denote a solder ball being at least partially surrounded (in particular with direct physical contact) by flux material and being arranged at least partially in said cavity. The solder ball may be only partially accommodated in the cavity in the stack. Hence, only part of a vertical spatial range between upper end and lower end of the solder ball may be located inside of the cavity, for instance the solder ball may protrude upwardly beyond the cavity.

In the context of the present application, the term "ball placement stencil with ball passage" may particularly denote a member comprising a sheet or plate having one or more through holes. The one or more through holes defining at least one ball passage may be shaped and dimensioned for allowing a solder ball to pass through the ball passage in such a way that, due to a partial or complete alignment between ball passage in ball placement stencil and cavity in component carrier structure, a solder ball will move through the ball passage and will thereby automatically be placed at least partially in said cavity.

In the context of the present application, the term "distance between the upper surface of stencil and external surface of component carrier structure" (see for example the sum of dimensions B3+B4 in Figure 1 or Figure 4) may particularly denote a vertical thickness of a sheet or plate of the ball placement stencil plus a distance between a bottom main surface of said sheet or plate and a top main surface of a plate- or sheet-shaped component carrier structure. Said distance may be defined by a spacing device connected to the bottom main surface of the sheet or plate of the ball placement stencil.

In the context of the present application, the term "diameter of solder ball" (see for example dimension Bl in Figure 1 or Figure 4) may particularly denote a maximum extension of the solder ball. When the solder ball is spherical, the diameter of the solder ball equals to twice the radius of the solder ball.

According to an exemplary embodiment of the invention, a component carrier structure (such as a preform of a PCB or a corresponding panel) with a (preferably laminated) layer stack has a recess-type cavity filled with flux material and has part of a solder ball embedded therein. By accommodating solder ball and flux material in a cavity of a component carrier structure, a solder process may be very reliable since a spatially correct positioning of the solder ball with respect to the component carrier structure may be strongly promoted by the cavity into which the solder ball may be automatically inserted by the influence of gravity and/or by a pushing device configured to push the at least one solder ball entirely at or below the upper surface of the stencil, such a brush device acting on an upper surface of the stencil. Also (in particular flowable) flux material may be forced to remain inside of the cavity rather than moving into undesired portions of the component carrier structure. During a solder process, the flux material may be removed partially or entirely.

Correspondingly, other exemplary embodiments of the invention may provide an apparatus for and a method of connecting a solder ball with a component carrier structure having a flux material-filled cavity. A ball placement stencil with ball passage may be brought in at least partial alignment with the cavity so that the solder ball can be pushed completely below an upper surface of the stencil and may fall down towards the cavity. When the distance between said upper surface of the stencil and the facing external surface of the component carrier structure is lower than a solder ball diameter, the solder ball can be reliably embedded in cavity and flux material therein. Descriptively speaking, a thickness of a stencil plate plus a distancing post thereof may be smaller than the thickness of the solder ball, which may ensure a spatially correct insertion of the solder ball into the cavity. Consequently, solder connec- tions with high reliability can be created for a component carrier structure. Advantageously, a high alignment accuracy may be achieved independently from variations of the ball diameter.

In the following, further exemplary embodiments of the component carrier structure, the apparatus, and the method will be explained.

In an embodiment, said at least one cavity opening on one of the external surfaces of the component carrier structure defines an external profile by an intersection of the at least one cavity with the respective external surface of the component carrier structure, wherein said at least one solder ball abuts against said external profile. Such an external profile may be an edge at a transition between a sidewall of the cavity and the planar external (or main) surface of the component carrier structure (see reference sign 116 in Figure 1 and Figure 4). When the solder ball has a direct physical contact with such an external profile, proper insertion of part of the solder ball into the cavity may be promoted. Abutment of the solder ball against the edge of the cavity may ensure a good alignment.

In an embodiment, in a plan view on the respective external surface of the component carrier structure, the at least one solder ball is positioned to exceed the respective external profile of the at least one cavity, wherein the ratio between (in the plan view) a maximum exceeding measure 01 (in the plan view) and the diameter (preferably an average diameter, or the radial maximum exceeding measure between a base profile and the recess) Bl of said at least one solder ball is within a range from 6.5% to 37.5%, particularly from 10% to 17%. Correspondingly, the stencil of the apparatus may be configured, in particular a thickness B3 of a planar plate and/or a height B4 of a spacing device may be configured, so that from the plan view of the respective external surface of the component carrier structure, the at least one solder ball is positioned to exceed an external profile of the at least one cavity, wherein the ratio between a maximum exceeding measure 01 and the diameter Bl of said at least one solder ball is within the range from 6.5% to 37.5%, particularly from 10% to 17%. These ranges are the footprint of a stencil having the thickness of the plate lower than the radius of the solder ball, avoiding failures concerning the balls positioning, for example avoiding that they are wrongly inserted and/or blocked between the component carrier and the stencil plate. To put it shortly, a limited portion of the solder ball may be located laterally outside of the cavity, and the solder ball may thus protrude laterally with respect to the external profile of the cavity by the dimension 01. A ratio between said lateral protrusion 01 and the ball diameter Bl is preferably within the above mentioned ranges for ensuring that the solder ball does not leave the cavity. 01 has been identified as a powerful design parameter for ensuring proper assembly of a solder ball in a cavity.

In an embodiment, said at least one solder ball is embedded in said at least one cavity in accordance with an embedding measure B6 (which may be measured along the thickness direction of the stack) defined by a maximum measure between a bottom profile of the embedded at least one solder ball and the respective external surface of the component carrier structure. Preferably, the ratio of said maximum measure and a diameter Bl of said at least one solder ball is within the range from 1.6% to 24%, particularly from 12.7% to 20.5%. Descriptively speaking, a certain portion of the solder ball may be located inside of the cavity, and the solder ball may protrude vertically into the cavity by the dimension B6. A ratio between said vertical embedding measure B6 and the ball diameter Bl is preferably within the above mentioned ranges for ensuring that the solder ball is reliably arranged at and in the cavity. B6 has been identified as a further powerful design parameter for ensuring proper assembly of a solder ball in a cavity.

In particular an appropriate choice of the combination of 01 and B6 in accordance with the two preceding paragraphs has turned out to allow to achieve highly appropriate results in terms of solder ball alignment in the cavity. Moreover, the range of the embedding measure may provide not only a proper alignment of the solder ball but also a due mechanical connection with the component carrier. Hence, this may ensure an appropriate mechanical connection.

In an embodiment, said maximum exceeding measure 01, said embedding measure B6, and said diameter Bl of said at least one solder ball are dimensioned according to the following formula:

Taking the aforementioned measure may ensure a proper relation between lateral and vertical offset. In particular, this may provide an excellent compromise for a proper alignment as well as a reliable connection of the solder ball with the component carrier.

In an embodiment, a plurality of solder balls are embedded in respective cavities each having the respective cavity opening on one (i.e. on the same) of the external surfaces. Hence, a plurality of cavities may be provided on one and the same exterior (or main) surface of the component carrier structure, and each of the cavities may be filled with a respective solder ball. By taking this measure, an assembly of plural solder balls may be formed with high reliability and high spatial accuracy, for instance for surface mounting electronic components with a large number of pads.

In an embodiment, the majority of the solder balls, preferably at least 80% of the solder balls, abut against the external profile of the respective cavity. The mentioned design rule may lead to an appropriate accuracy of alignment. Moreover, said design rule may be the fingerprint of a preciseness of the apparatus.

In an embodiment, the majority of solder balls (in particular at least 80% of the solder balls) abutting against the external profile of the respective cavity abut against the respective cavity in the same direction of the external profile of the respective cavity when viewed from the plan view. For example, said majority (and preferably at least 80%) of the solder balls may abut against the external profile of the respective cavity all on the right-hand side (or all on the left-hand side). In other words, said majority may, with respect to a central vertical axis of the respective cavity, all be shifted towards and located on one and the same side relative to said vertical axis.

In an embodiment, a diameter Bl of said at least one solder ball is within the range of 5 pm to 300 pm, particularly 40 pm to 100 pm. When assembling solder balls of the mentioned small dimensions, proper positioning accuracy may be of utmost advantage and handling may be delicate.

In an embodiment, a diameter B2 of said at least one cavity is within the range of 5 pm to 400 pm, particularly 50 pm to 120 pm. In an embodiment, a depth of said at least one cavity is within the range of 1 pm to 100 pm, particularly 10 pm to 40 pm. For example, a thickness of a planar plate (with ball passage(s)) of the ball placement stencil may be in a range from 20 pm to 50 pm, preferably in a range from 22 pm to 40 pm. For instance, a thickness of a spacing device (extending from a bottom of the plate) of the ball placement stencil may be in a range from 25 pm to 60 pm, preferably in a range from 25 pm to 40 pm. Most preferred may be a plate thickness of 25 pm and a spacing device thickness of 30 pm when handling solder balls having a diameter of 63 pm.

As already mentioned, said at least one cavity opening on one of the external surfaces of the component carrier structure may define an external profile by an intersection of the at least one cavity with the respective external surface of the component carrier structure, in one embodiment. Accordingly, an embodiment of the apparatus may have a configuration of the stencil to be movable so that during solder ball embedding said at least one solder ball abuts against said external profile. For this purpose, the apparatus may comprise a control unit configured for controlling motion of the stencil with respect to the component carrier structure accordingly.

In an embodiment, the distance B3+B4 between said upper surface of the stencil and the respective external surface of the component carrier structure is configured so that said at least one solder ball is embedded in said at least one cavity in accordance with an embedding measure B6 defined by a maximum measure between a bottom profile of the embedded at least one solder ball and the respective external surface of the component carrier structure, wherein the ratio of said maximum measure B6 and a diameter Bl of said at least one solder ball is within the range from 1.6% to 24%, particularly from 12.7% to 20.5%. As already mentioned above, embedding measure B6 may indicate how deep the solder ball extends into the cavity by defining an appropriate range of values corresponding to a ratio between embedding measure B6 and ball diameter Bl. By a control unit, operation of the stencil may be adjusted so that the design rule in accordance with said ranges is fulfilled. As a result, the above-mentioned advantages may be achieved.

In an embodiment, the stencil comprises a planar plate comprising said at least one ball passage (and in particular defining said upper surface of the stencil) and a spacing device (for example a post, which may protrude down- wardly from a bottom main surface of the planar plate) provided on the surface of the stencil in front of and in contact with the respective external surface (preferably on the opposed side of the upper surface of the stencil) of the component carrier structure when the stencil is on its working position with respect to the component carrier structure. In such an embodiment, the planar plate with its cavity or cavities may be placed in parallel to the (preferably plate-shaped) component carrier structure, and the spacing device in between may maintain a target distance between planar stencil plate and component carrier structure. The thickness of the spacing device may be adjusted to meet the above described design rule regarding stencil plate thickness and spacing device thickness versus solder ball diameter. Furthermore, the presence of the spacing device may disable an unintentional direct physical contact between stencil plate and component carrier structure. This may prevent, for example, a direct physical contact between flux material and ball placement stencil which might unintentionally remove flux material out of the cavity or harm the stencil.

In an embodiment, a thickness B3 of the planar plate is smaller than half of the diameter Bl of the at least one solder ball. In particular, the thickness of the planar plate may be less than a radius of a spherical solder ball. This may reliably prevent erroneously assembled solder balls and may contribute to achieve the above-mentioned advantages.

In an embodiment, the external profile of the at least one cavity is circular with a cavity diameter B2. When the at least one ball passage contacts at a contact point the at least one solder ball on the opposite side (in a planar view) of an abutment point of the at least one solder ball with the external profile of the respective cavity, a distance B5 between said contact point and the external profile of the respective cavity opposite to said abutment point may preferably correspond to the following formula:

₅₅ > B2 - (Bl - 01 - 02) + (B7 - B2)

In the aforementioned formula, 02 is a maximum exceeding lateral measure of the at least one solder ball exceeding said contact point, wherein 01 is a maximum exceeding lateral measure of the at least one solder ball exceeding the respective external profile of the at least one cavity, and B7 is an opening width of the stencil, i.e. a diameter of the ball passage. The mentioned design rule provides a correlation between dimensions and positions of component carrier structure with cavity, solder ball and the ball placement stencil of the apparatus. When this design rule is fulfilled, it may be possible to avoid failures due to the high pressure of the stencil against the solder ball (especially from the profile of the stencil aperture against the ball) as well as the wrong placement of said solder ball between the component carrier and the lower surface of the stencil planar plate. A cavity within an exterior circular edge may properly match with a spherical solder ball.

In an embodiment, the external profile of the at least one cavity is circular with a cavity diameter B2. When the at least one ball passage contacts at a contact point the at least one solder ball on the opposite side (in a planar view) of an abutment point of the at least one solder ball with the external profile of the respective cavity, B5 is a distance between said contact point and the external profile of the respective cavity opposite to said abutment point. In such a scenario, it may be advantageous when the ratio of said distance B5 and the diameter Bl of the at least one solder ball is within the range of 26% and 32.5%. Operating the apparatus so that the solder ball position with respect to the cavity in the component carrier structure meets that described condition, proper alignment between solder ball and cavity may be ensured. Furthermore, this may lead to a reliable failure prevention.

In an embodiment, said apparatus is configured to push the at least one solder ball entirely at or below the upper surface of the stencil through a brush device acting on an upper surface of the stencil. This action can be achieved by a brush device, which may be configured as a ball brush sweeping the solder ball on the stencil. It is also possible that the supply of solder balls to the one or ball passages of the ball placement stencil is accomplished by a squeegee, or any other appropriate ball applicator.

In an embodiment, a stack of the component carrier structure or of the component carrier comprises at least one electrically insulating layer structure and at least one electrically conductive layer structure. For example, the component carrier may be a laminate of the mentioned electrically insulating layer structure(s) and electrically conductive layer structure(s), in particular formed by applying mechanical pressure and/or thermal energy. The mentioned stack may provide a plate-shaped component carrier capable of providing a large mounting surface for further components and being nevertheless very thin and compact.

In an embodiment, the component carrier structure or component carrier is shaped as a plate. This contributes to the compact design, wherein the component carrier nevertheless provides a large basis for mounting components thereon. Furthermore, in particular a naked die as example for an embedded electronic component, can be conveniently embedded, thanks to its small thickness, into a thin plate such as a printed circuit board.

In an embodiment, a component carrier obtained from the component carrier structure is configured as one of the group consisting of a printed circuit board, a substrate (in particular an IC substrate), and an interposer.

In the context of the present application, the term "printed circuit board" (PCB) may particularly denote a plate-shaped component carrier which is formed by laminating several electrically conductive layer structures with several electrically insulating layer structures, for instance by applying pressure and/or by the supply of thermal energy. As preferred materials for PCB technology, the electrically conductive layer structures are made of copper, whereas the electrically insulating layer structures may comprise resin and/or glass fibers, so-called prepreg or FR.4 material. The various electrically conductive layer structures may be connected to one another in a desired way by forming holes through the laminate, for instance by laser drilling or mechanical drilling, and by partially or fully filling them with electrically conductive material (in particular copper), thereby forming vias or any other through-hole connections. The filled hole either connects the whole stack, (through-hole connections extending through several layers or the entire stack), or the filled hole connects at least two electrically conductive layers, called via. Similarly, optical interconnections can be formed through individual layers of the stack in order to receive an electro-optical circuit board (EOCB). Apart from one or more components which may be embedded in a printed circuit board, a printed circuit board is usually configured for accommodating one or more components on one or both opposing surfaces of the plateshaped printed circuit board. They may be connected to the respective main surface by soldering. A dielectric part of a PCB may be composed of resin with reinforcing fibers (such as glass fibers).

In the context of the present application, the term "substrate" may particularly denote a small component carrier. A substrate may be a, in relation to a PCB, comparably small component carrier onto which one or more components may be mounted and that may act as a connection medium between one or more chip(s) and a further PCB. For instance, a substrate may have substantially the same size as a component (in particular an electronic component) to be mounted thereon (for instance in case of a Chip Scale Package (CSP)). In another embodiment, the substrate may be substantially larger than the assigned component (for instance in a flip chip ball grid array, FCBGA, configuration). More specifically, a substrate can be understood as a carrier for electrical connections or electrical networks as well as component carrier comparable to a printed circuit board (PCB), however with a considerably higher density of laterally and/or vertically arranged connections. Lateral connections are for example conductive paths, whereas vertical connections may be for example drill holes. These lateral and/or vertical connections are arranged within the substrate and can be used to provide electrical, thermal and/or mechanical connections of housed components or unhoused components (such as bare dies), particularly of IC chips, with a printed circuit board or intermediate printed circuit board. Thus, the term "substrate" also includes "IC substrates". A dielectric part of a substrate may be composed of resin with reinforcing particles (such as reinforcing spheres, in particular glass spheres).

The substrate or interposer may comprise or consist of at least a layer of glass, silicon (Si) and/or a photoimageable or dry-etchable organic material like epoxy-based build-up material (such as epoxy-based build-up film) or polymer compounds (which may or may not include photo- and/or thermosensitive molecules) like polyimide or polybenzoxazole.

In an embodiment, the at least one electrically insulating layer structure comprises at least one of the group consisting of a resin or a polymer, such as epoxy resin, cyanate ester resin, benzocyclobutene resin, bismaleimide-tria- zine resin, polyphenylene derivate (e.g. based on polyphenylenether, PPE), polyimide (PI), polyamide (PA), liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE) and/or a combination thereof. Reinforcing structures such as webs, fibers, spheres or other kinds of filler particles, for example made of glass (multilayer glass) in order to form a composite, could be used as well. A semi-cured resin in combination with a reinforcing agent, e.g. fibers impregnated with the above-mentioned resins is called prepreg. These prepregs are often named after their properties e.g. FR4 or FR5, which describe their flame retardant properties. Although prepreg particularly FR4 are usually preferred for rigid PCBs, other materials, in particular epoxy-based build-up materials (such as build-up films) or photoimageable dielectric materials, may be used as well. For high frequency applications, high-frequency materials such as polytetrafluoroethylene, liquid crystal polymer and/or cyanate ester resins, may be preferred. Besides these polymers, low temperature cofired ceramics (LTCC) or other low, very low or ultra-low DK materials may be applied in the component carrier as electrically insulating structures.

In an embodiment, the at least one electrically conductive layer structure comprises at least one of the group consisting of copper, aluminum, nickel, silver, gold, palladium, tungsten, magnesium, carbon, (in particular doped) silicon, titanium, and platinum. Although copper is usually preferred, other materials or coated versions thereof are possible as well, in particular coated with supra-conductive material or conductive polymers, such as graphene or poly(3,4-ethylenedioxythiophene) (PEDOT), respectively.

At least one component may be embedded in and/or surface mounted on the stack. The component and/or the at least one further component can be selected from a group consisting of an electrically non-conductive inlay, an electrically conductive inlay (such as a metal inlay, preferably comprising copper or aluminum), a heat transfer unit (for example a heat pipe), a light guiding element (for example an optical waveguide or a light conductor connection), an electronic component, or combinations thereof. An inlay can be for instance a metal block, with or without an insulating material coating (IMS-in- lay), which could be either embedded or surface mounted for the purpose of facilitating heat dissipation. Suitable materials are defined according to their thermal conductivity, which should be at least 2 W/mK. Such materials are often based, but not limited to metals, metal-oxides and/or ceramics as for instance copper, aluminium oxide (AI2O3) or aluminum nitride (AIN). In order to increase the heat exchange capacity, other geometries with increased surface area are frequently used as well. Furthermore, a component can be an active electronic component (having at least one p-n-junction implemented), a passive electronic component such as a resistor, an inductance, or capacitor, an electronic chip, a storage device (for instance a DRAM or another data memory), a filter, an integrated circuit (such as field-programmable gate array (FPGA), programmable array logic (PAL), generic array logic (GAL) and complex programmable logic devices (CPLDs)), a signal processing component, a power management component (such as a field-effect transistor (FET), metal- oxide-semiconductor field-effect transistor (MOSFET), complementary metal- oxide-semiconductor (CMOS), junction field-effect transistor (JFET), or insulated-gate field-effect transistor (IGFET), all based on semiconductor materials such as silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), gallium oxide (GazOs), indium gallium arsenide (InGaAs), indium phosphide (InP) and/or any other suitable inorganic compound), an optoelectronic interface element, a light emitting diode, a photocoupler, a voltage converter (for example a DC/DC converter or an AC/DC converter), a cryptographic component, a transmitter and/or receiver, an electromechanical transducer, a sensor, an actuator, a microelectromechanical system (MEMS), a microprocessor, a capacitor, a resistor, an inductance, a battery, a switch, a camera, an antenna, a logic chip, and an energy harvesting unit. However, other components may be embedded in the component carrier. For example, a magnetic element can be used as a component. Such a magnetic element may be a permanent magnetic element (such as a ferromagnetic element, an antiferromagnetic element, a multiferroic element or a ferrimagnetic element, for instance a ferrite core) or may be a paramagnetic element. However, the component may also be an IC substrate, an interposer or a further component carrier, for example in a board-in-board configuration. The component may be surface mounted on the component carrier and/or may be embedded in an interior thereof. Moreover, also other components, in particular those which generate and emit electromagnetic radiation and/or are sensitive with regard to electromagnetic radiation propagating from an environment, may be used as component. In an embodiment, the component carrier obtained from the component carrier structure is a laminate-type component carrier. In such an embodiment, the component carrier is a compound of multiple layer structures which are stacked and connected together by applying a pressing force and/or heat.

After processing interior layer structures of the component carrier, it is possible to cover (in particular by lamination) one or both opposing main surfaces of the processed layer structures symmetrically or asymmetrically with one or more further electrically insulating layer structures and/or electrically conductive layer structures. In other words, a build-up may be continued until a desired number of layers is obtained.

After having completed formation of a stack of electrically insulating layer structures and electrically conductive layer structures, it is possible to proceed with a surface treatment of the obtained layers structures or component carrier.

In particular, an electrically insulating solder resist may be applied to one or both opposing main surfaces of the layer stack or component carrier in terms of surface treatment. For instance, it is possible to form such a solder resist on an entire main surface and to subsequently pattern the layer of solder resist so as to expose one or more electrically conductive surface portions which shall be used for electrically coupling the component carrier to an electronic periphery. The surface portions of the component carrier remaining covered with solder resist may be efficiently protected against oxidation or corrosion, in particular surface portions containing copper.

It is also possible to apply a surface finish selectively to exposed electrically conductive surface portions of the component carrier in terms of surface treatment. Such a surface finish may be an electrically conductive cover material on exposed electrically conductive layer structures (such as pads, conductive tracks, etc., in particular comprising or consisting of copper) on a surface of a component carrier. If such exposed electrically conductive layer structures are left unprotected, then the exposed electrically conductive component carrier material (in particular copper) might oxidize, making the component carrier less reliable. A surface finish may then be formed for instance as an interface between a surface mounted component and the component carrier. The surface finish has the function to protect the exposed electrically conductive layer structures (in particular copper circuitry) and enable a joining process with one or more components, for instance by soldering. Examples for appropriate materials for a surface finish are Organic Solderability Preservative (OSP), Electroless Nickel Immersion Gold (ENIG), Electroless Nickel Immersion Palladium Immersion Gold (ENIPIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), gold (in particular hard gold), chemical tin (chemical and electroplated), nickel-gold, nickel-palladium, etc. Also nickel-free materials for a surface finish may be used, in particular for high-speed applications. Examples are ISIG (Immersion Silver Immersion Gold), and EPAG (Eletroless Palladium Autocatalytic Gold).

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

Figure 1 illustrates a cross-sectional view of an apparatus to connect at least one solder ball with a component carrier structure according to an exemplary embodiment of the invention.

Figure 2 illustrates a plan view of an apparatus to connect at least one solder ball with a component carrier structure according to an exemplary embodiment of the invention.

Figure 3 illustrates a cross-sectional view, and a detail thereof, of an apparatus to connect at least one solder ball with a component carrier structure according to an exemplary embodiment of the invention.

Figure 4 illustrates a cross-sectional view of a detail of an apparatus to connect at least one solder ball with a component carrier structure according to an exemplary embodiment of the invention.

Figure 5 to Figure 7 illustrate different plan views of stencil ball passages and corresponding cavities for applying solder balls to a component carrier structure.

Figure 8 and Figure 9 illustrate different plan views of stencil ball passages and corresponding cavities for applying solder balls to a component carrier structure.

Figure 10 and Figure 11 illustrate diagrams indicating target ranges of solder balls applied to a component carrier structure according to exemplary embodiments of the invention.

The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs.

Before referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the invention have been developed.

According to an exemplary embodiment of the invention, a layer stacktype component carrier structure (such as a printed circuit board (PCB) being presently manufactured, or a PCB panel) is equipped with one or more indentation-type cavities filled with flux material. A respective solder ball may be assembled partially inside of a respective cavity in contact with the flux material therein. By assembling solder balls with the bottom portion thereof inside of cavities of the component carrier structure, creation of a solder connection with high spatial accuracy may be made possible thanks to the aligning effect of the recessed cavities.

A corresponding apparatus for creating a respective connection of one or more solder balls with a component carrier structure comprising a cavity profile as described in the preceding paragraph may have a ball placement stencil with one or more ball passages through which a respective solder ball may fall downwardly towards the assigned cavity filled with flux material. Said apparatus may push said solder ball completely to (for example at an upper profile end of the solder ball) and/or below (for instance beneath the upper profile end) an upper surface of the stencil. Highly advantageously, a distance (see reference signs B3+B4 in Figure 1 and Figure 4) between said upper surface of the stencil and the external surface (having the at least one cavity formed therein) of the component carrier structure can be smaller than a (for instance maximum or constant) diameter (see reference sign Bl in Figure 1 and Figure 4) of the respective solder ball. This may ensure that a bottom portion of said solder ball is reliably embedded in the assigned cavity and is functionally connected with said flux material. To reliably achieve this, a highly advantageous design parameter can be that a thickness of a stencil plate plus a thickness of a spacing device extending from a bottom of the stencil plate up to the upper exterior surface of the component carrier structure is smaller than the thickness (or diameter) of the solder ball. Additionally or alternatively, it may also be advantageous when the thickness of the stencil plate is less than the radius of the solder ball (which may correspond to half of the diameter of the solder ball). When the latter design rule is fulfilled, the stencil plate can abut against the solder ball and can ensure a correct assembly of the ball in the cavity. This may avoid undue tensions of the lateral profile of the stencil ball passage against the respective ball, the latter eventually abutting against the external profile of the cavity, causing unpredicted deformation of the cavity and/or the ball and/or the stencil, as well as unpredicted placement (shift) of the ball, for example between the component carrier (out of the cavity) and the stencil.

In particular, an exemplary embodiment of the invention provides a ball placement stencil being particularly appropriate for assembling solder balls embodied as microballs. Such a ball placement stencil with a vertical thickness of stencil plate and spacing device smaller than a diameter of the solder ball may lead to a pronounced improvement of yield. The described configuration may mitigate or even eliminate a conventional ball shift issue. This may increase yield and may significantly reduce a down time to fix a corresponding issue. In particular, it has been identified that there is the opportunity to reduce or even minimize a printing space for yield improvement during solder ball assembly. In particular, small thickness and/or small tension of a ball placement stencil have turned out as advantageous measures to improve yield and accuracy of solder ball assembly on a component carrier structure.

For the example of solder balls having a diameter of 63 pm, it has turned out to be highly appropriate to reduce an overall thickness of stencil plate plus spacing device thereunder to 55 pm. A stencil thickness of 25 pm turned out as advantageous. A thickness of a spacing device, i.e. post thickness, of 30 pm led to highly appropriate results. When taking these measures, a ball printing maximum offset could be reduced by more than 50% (to 10.5 pm). In the described example, a ball alignment range from 14.4 pm to 18.9 pm could be achieved.

More generally, an exemplary embodiment of the invention may provide an apparatus with ball placement stencil having a stencil plate thickness in a range from 20 pm to 25 pm. An opening diameter of a cavity may be in a range from 70 |jm to 78 |jm. This may allow to reduce a ball printing maximum offset and to improve shrinkage impact on an alignment offset. Furthermore, a tension may be selected in the range from 11.5 N to 18 N, preferably in a range from 13 N to 16 N. This may promote sweeping the solder ball into the cavity. An ideal target distance between ball placement stencil and panel or table gap is zero.

Operating the stencil with limited tension may advantageously cause the stencil to fully touch the table and decrease the gap (which is advantageously as small as possible) between stencil on the one hand and table or panel on the other hand, which may lead to an assembly of the solder ball print in the cavity. Advantageously, exemplary embodiments of the invention may prevent an excessive ball shift on the panel surface. With the above mentioned limited tension, it may be possible to reliably absorb the stencil on a table even when the panel encounters warpage issue. Consequently, no ball shift out of the cavity will occur when printing. When limiting the stencil overall thickness (i.e. stencil plate thickness), the maximum offset for the solder ball (see dimension 01 in Figure 1 and Figure 4) can be kept sufficiently small so that the solder ball will not be located outside of the cavity. To put it shortly, an exemplary embodiment of the invention controls a limitation of the ball shift, thereby eliminating a conventional main defect cause in automatic optical inspection of solder bumps. Furthermore, the down time of a corresponding manufacturing apparatus (which has been significant in conventional approaches to tackle errors) can be significantly reduced.

According to an exemplary embodiment, a stencil thickness may be reduced for reducing a printing space when assembling solder balls. Moreover, it may be possible to decrease applied tension in order to reduce a gap between stencil and panel. A stencil thickness decrease and a tension decrease action may be taken in order to reduce the space for ball printing, reducing or even minimizing a printing location and avoiding ball shift issues. This may increase the yield of component carrier manufacture.

Exemplary applications of exemplary embodiments of the invention are integrated circuit substrates and component carriers being manufactured by a microball process.

Figure 1 illustrates a cross-sectional view of an apparatus 120 to connect solder balls 114 with a component carrier structure 100, which is here embodied as a panel for manufacturing printed circuit boards (PCBs) or integrated circuit (IC) substrates, according to an exemplary embodiment of the invention. Figure 2 illustrates a plan view of the apparatus 120. Figure 3 illustrates a cross-sectional view and a detail of said apparatus 120. Figure 4 illustrates a cross-sectional view of a detail of the apparatus 120.

First referring to Figure 2 and Figure 3, apparatus 120 comprises a mounting table 150 on which the component carrier structure 100 to be processed is mounted. A dummy plate 152 surrounds the component carrier structure 100 on the mounting table 150. The dummy plate 152 may protect a stencil 122 of apparatus 120 and may avoid a direct contact between stencil 122 and table 150 which might harm the stencil 122. Ball placement stencil 122 is arranged on the component carrier structure 100 and on the dummy plate 152. Figure 2 also illustrates a vacuum hole 154 which may be used for firmly holding the component carrier structure 100 on the table 150. The cross-section of Figure 3 is along a cutting line A-A' of Figure 2. As indicated with reference sign 156 in Figure 3, the ball placement stencil 122 has an indentation in lateral gaps between the component carrier structure 100 and the dummy plate 152. Advantageously, the gap between ball placement stencil 122 on the one hand and table 150 as well as component carrier structure 100 on the other hand can be advantageously decreased as much as possible.

Now referring to detail 158 in Figure 3, it can be seen that the ball placement stencil 122 of apparatus 120 is placed on top of component carrier structure 100 preferably in such a way that through hole-type ball passages 124 in a stencil plate 126 are aligned (at least partially) with cavities 108 formed in an external surface 110 (which is an upper main surface according to Figure 3) of component carrier structure 100. At a bottom of each cavity 108, a respective metallic pad may be formed (not shown). The solder balls 114 may then be passed through the ball passages 124 so as to be reliably inserted at least partially into an assigned one of the cavities 108. As can be taken from detail 158 as well, a spacing device 128 is formed at (for instance integrally formed with) a bottom side of planar plate 126 so as to bridge a vertical distance between a bottom side of the planar plate 126 and the external surface 110 of the component carrier structure 100. A further detail 160 indicated within detail 158 of Figure 3 shows how a solder ball 114 is printed in a cavity 108. Such a scenario will be explained in the following in further detail referring to Figure 1 and, with further magnification, referring to Figure 4.

Now also referring to Figure 1 and Figure 4, apparatus 120 serves for connecting solder balls 114 with panel-type component carrier structure 100.

For this connection, several dimensions and parameters may be relevant, which will be explained in the following:

Bl : diameter of solder ball 114

B2: horizontal top diameter of cavity 108

B3: vertical thickness of planar plate 126 of ball placement stencil 120

B4: vertical thickness of spacing body 128 of ball placement stencil 120

B5: lateral alignment offset between ball passage 124 and cavity 108

B6: insertion depth of solder ball 114 into cavity 108 (=B1-B3-B4)

B7: horizontal diameter of ball passage 124

D: design distance from exterior edge of cavity 108 to remote bottom edge of planar plate 126 (i.e. D may relate to a design distance corresponding to a transverse connection from the top edge of the cavity 108 to the bottom edge of the planar plate 126), wherein both said edges may contact solder ball 114

01 : maximum horizontal offset between surface of solder ball 114 to exterior edge of cavity 108

02: maximum horizontal offset between surface of solder ball 114 to contact point 130 between solder ball 114 and planar plate 126 of ball placement stencil 120 (see detail 170 in Figure 4)

Also referring to a detail 162 of Figure 4, the component carrier structure 100 comprises a laminated layer stack 102 comprising electrically conductive layer structures 104 and electrically insulating layer structures 106. For example, the electrically conductive layer structures 104 may comprise patterned metal layers (such as patterned copper foils or patterned deposited copper layers) and vertical through connections, for example copper filled vias, which may be created by drilling and plating. The electrically insulating layer structures 106 may comprise a respective resin (such as a respective epoxy resin), preferably comprising reinforcing particles therein (for instance glass fibers or glass spheres). For example, the electrically insulating layer structures 106 may be made of FR4. The electrically insulating layer structures 106 may also comprise resin layers being free of glass (in particular glass fibers).

A top layer of stack 102 can be defined by a layer of solder resist 166. Moreover, a plurality of cavities 108 are formed in the external surface 110 of the component carrier structure 100 which faces the ball placement stencil 122. More specifically, the cavities 108 may be formed in the solder resist 166 on top of the stack 102. Flux material 112 fills each of said cavities 108. Descriptively speaking, the flux material 112 may support a soldering process, for instance may suppress oxidation or corrosion of exposed metal structures involved in such a soldering process. In the shown embodiment, the cavities 108 are completely filled with flux material 112. It is also possible that the cavities 108 are only partially filled with flux material 112.

As best seen in Figure 1, apparatus 120 is configured to push supplied solder balls 114 from above the planar plate 126 below the upper surface of the stencil 122. Supply of the solder balls 114 to the upper side of the ball placement stencil 122 can be accomplished by a brush device 132 acting on an upper surface of the stencil 122. For instance, brush device 132 may be embodied as ball brush sweeping the solder balls 114 on the ball placement stencil 122. Alternatively, it is also possible to supply the solder balls 114 to the upper side of the ball placement stencil 122 by a squeegee (not shown) or the like.

As already mentioned, the apparatus 120 comprises ball placement stencil 122 having a plurality of ball passages 124 arranged side by side and extending completely through the planar plate 126. Apparatus 120 is configured to allow the supplied solder balls 114 to fall towards an assigned cavity 108 and into the flux material 112 when the respective ball passage 124 is partially or completely aligned with the respective cavity 108. Figure 4 shows a partial alignment between the illustrated ball passage 124 and the shown cavity 108 into which the shown solder ball 114 is partially inserted. Hence, the apparatus 120 is configured so that when the stencil 122 is in its working position with respect to the component carrier structure 100 (as for instance shown in Figure 4), the respective solder ball 114 is pushed to be entirely at or below an upper surface 164 of the stencil 122, and consequently a bottom portion of said solder ball 114 enters its cavity 108 and will get into direct physical contact with the flux material 112 therein. In Figure 1, the vertically uppermost profile surface area of the solder ball 114 is aligned with the upper surface 164 of the ball placement stencil 122.

Advantageously, the apparatus 120 is designed so that a distance B3 + B4 between said upper surface 164 of the stencil 122 and the respective external surface 110 of the component carrier structure 100 is smaller than a diameter Bl of the solder ball 114. This may ensure that the solder ball 114 is at least partially embedded in said cavity 108 and in said flux material 112. Thus, it may be advantageous when the vertical thickness B3+B4 of the ball placement stencil 120 is smaller than the diameter Bl of the preferably spherical solder ball 114, since this may promote the solder ball 114 being reliably partially embedded inside of the cavity 108.

Moreover, the respective cavity 108 which opens on the external surface 110 of the component carrier structure 100 defines a preferably circular external profile 116 as an intersection of the cavity 108 with the external surface 110 of the component carrier structure 100. Advantageously, the stencil 122 is configured to be movable so that, during solder ball embedding, the respective solder ball 114 abuts against said external profile 116 (see bottom left-hand side of solder ball 114 in Figure 4).

Advantageously, the distance B3+B4 between said upper surface of the stencil 122 and the external surface 110 of the component carrier structure 100 is configured so that said at least one solder ball 114 is embedded in said at least one cavity 108 in accordance with embedding measure B6. The latter is defined by a maximum vertical measure between a bottom profile of the embedded solder ball 114 and the external surface 110 of the component carrier structure 100. Preferably, the ratio B6:B1 of said maximum measure B6 and the diameter Bl of the solder ball 114 is within a range from 1.6% to 24%, preferably from 12.7% to 20.5%. This ensures that the solder ball 114 is reliably inside of the cavity 108 while simultaneously guaranteeing that solder ball 114 sufficiently protrudes beyond the external surface 110 which leads to a reliable solder connection. As already mentioned, the ball placement stencil 122 comprises the topsided perforated planar plate 126 with its through hole-type ball passages 124. Furthermore, the ball placement stencil 122 comprises the above-mentioned bottom-sided and post-type spacing device 128 extending downwardly from the bottom surface of the planar plate 126. Spacing device 128 faces the and is in contact with the external surface 110 of the component carrier structure 100 when the stencil 122 is on its working position with respect to the component carrier structure 100. Descriptively speaking, spacing device 128 maintains a predefined spacing B4 between the bottom of the planar plate 126 and the external surface 110 of the component carrier structure 100. Preferably, thickness B3 of the planar plate 126 is smaller than half of the diameter Bl of the solder ball 114. This promotes reliable insertion of solder ball 114 in cavity 108.

In a plan view on the external surface 110 of the component carrier structure 100, the solder ball 114 is positioned to exceed the external profile 116 of the cavity 108 (on the left-hand side according to Figure 4) by maximum lateral exceeding measure 01. Preferably, the ratio 01 : Bl between the maximum lateral exceeding measure 01 and the diameter Bl of said solder ball 114 is within the range from 6.5% to 37.5%, preferably from 10% to 17%. This ensures a proper alignment between solder ball 114 and cavity 108 and thereby promotes a correct positioning.

As already mentioned, the external profile 116 of the respective cavity 108 may be preferably circular with a cavity diameter B2. As shown in Figure 4, the ball passage 124, for passing solder balls 114, contacts at a contact point 130 the solder ball 114 on the opposite side (i.e. on the top right-hand side according to Figure 4) of an abutment point (i.e. on the bottom left-hand side according to Figure 4) of the solder ball 114 with the external profile 116 of the cavity 108. Distance B5 between said contact point 130 and the external profile 116 of the respective cavity 108 opposite (i.e. on the bottom righthand side according to Figure 4) to said abutment point corresponds to the following formula:

In said formula or equation, 02 is the maximum exceeding measure of the solder ball 114 exceeding said contact point 130 (compare detail 170 in Figure 4). In other words, 02 is the distance, in a planar view, between the external profile of the solder ball 114 and said contact point 130. Again referring to the above formula or equation, 01 is the maximum exceeding measure of the solder ball 114 exceeding the external profile 116 of the cavity 108 on the left-hand side according to Figure 4. Moreover, B7 is the opening width or diameter of the ball passage 124 of the ball placement stencil 122. Referring to the above equation, the alignment offset should be sufficiently small to avoid that the solder ball 114 gets stuck.

It is recalled that the external profile 116 of the cavity 108 can be preferably circular with cavity diameter B2. When an edge of the ball passage 124 contacts at contact point 130 the solder ball 114 on the opposite side of the abutment point of the solder ball 114 with the external profile 116 of the cavity 108, B5 is the distance between said contact point 130 and the external profile 116 of the cavity 108 opposite to said abutment point. Preferably, the ratio B5: B1 of said distance B5 and the constant or maximum diameter Bl of the solder ball 114 is within the range of 26% and 32.5%. This ensures correct placement of a solder ball 114 without excessive demands on alignment accuracy.

Moreover, it may be preferred that said maximum exceeding measure 01, said embedding measure B6, and said diameter Bl of said solder ball 114 are dimensioned according to the following formula:

Referring to the above equation or formula, the maximum ball shift should be so that the solder ball 114 cannot move out of the cavity 108. Furthermore, an additional equation relates to the above equation with 01 being substituted by 02 and B6 being substituted by B3. Also referring to the equation with said substitutions, the maximum ball shift should be so that the solder ball 114 cannot move out of the cavity 108.

As shown in detail 158 in Figure 3, a plurality of solder balls 114 are embedded in respective cavities 108 each having the opening on the same ex- ternal surface 110, i.e. the upper main surface of stack 102 according to Figure 3. Although not shown, it may be possible that at least 80% of the solder balls 114 abut against the external profile 116 of the respective cavity 108. Furthermore, it may be possible that at least 80% of the solder balls 114 abut against the respective cavity 108 in the same direction of the external profile 116 of the respective cavity 108 in a plan view. For instance referring to Figure 4, the illustrated solder ball 114 abuts against the external profile 116 of cavity 108 on the left-hand side. For example, at least 80% of the solder balls 114 may abut against the external profile 116 of cavity 108 on the same side, for instance on the left-hand side.

For example, the diameter Bl of each solder ball 114 may be in the range from 40 pm to 100 pm, for example 63 pm or 75 pm. Preferably, the sum of the partial thicknesses B3 and B4 of the ball placement stencil 122 may be smaller than the diameter Bl, for instance may be at least 2% smaller, may be at least 5% smaller, or may be at least 10% smaller. This ratio would correspond to B6, namely within a range from 1.6% to 24%, particularly from 12.7% to 20.5%. As an example, when solder balls 114 with diameter Bl of 63 pm are handled, B3 may be 25 pm and B4 may be 30 pm. Also advantageously, B3 can be smaller than half of the diameter Bl, for instance may be at least 3% smaller, may be at least 7% smaller, or may be at least 15% smaller than half of the diameter Bl. When following these design rules, ball shift out issues may be reliably prevented. With a sufficiently small plate and post thickness of the stencil 122, it may be possible to reduce the ball printing space. After ball brush, it is possible to sweep the solder ball 114 on the solder resist opening or cavity 108, and this may press the solder ball 114 into the cavity 108 to avoid ball shift out issues. In particular, the shown embodiments may significantly reduce the risk that the solder ball 114 gets stuck between cavity 108 and stencil 122.

The illustrated design of ball placement stencil 122 may be operated with a low tension which may cause the stencil 122 to fully touch the table 150 and decrease the gap (see reference sign 156 in Figure 3) between stencil 122 on the one hand and table 150 or component carrier structure 100 on the other hand. This may lead to a reliable ball print in the respective cavity 108.

Referring to Figure 5, a maximum ball shift is indicated with reference sign 182. For the stencil overall thickness range, the following condition may be fulfilled according to exemplary embodiments of the invention: Stencil overall thickness - solder resist thickness < stencil overall thickness < ball size - 1 pm.

Referring to Figure 6, a pad location 184 (which corresponds to a bottom of cavity 108) is compared with a stencil aperture 186 (which corresponds to the ball passage 124). An alignment offset, corresponding to the above defined dimension B5, is indicated in Figure 6 with reference sign 188.

With the design rules mentioned above, and in particular with the limited stencil thickness B3+B4, the maximum ball shift 01 may be acceptably small, and the alignment offset B5 may also be acceptably small. In order to increase the alignment offset limitation to avoid that the solder ball 114 gets stuck on the stencil aperture, i.e on ball passage 124, it may be possible to consider an increase of the stencil opening which may have an impact on ball accuracy and stencil accuracy. Advantageously, a maximum opening may be designed to fulfill the following condition: Maximum opening < design pitch - ball accuracy - stencil accuracy.

Referring to Figure 7, a same design on pad diameter is illustrated on the left-hand side with reference sign 190. On the right side, a different stencil aperture size is plotted with reference sign 192.

A first scenario 194 in Figure 8 shows a diagram which relates to a conventional approach and plots along an abscissa 191 a shrinkage value in x- direction and along an ordinate 193 a shrinkage value in y-direction. The two illustrated circles relate to two different types of stencils and show a poor match. This poor match can also be taken from the corresponding images of Figure 9 relating to the first scenario 194.

A second scenario 196 in Figure 8 shows a diagram which relates to a stencil design according to an exemplary embodiment of the invention and plots along an abscissa 191 a shrinkage value in x-direction and along an ordinate 193 a shrinkage value in y-direction. The two illustrated circles relate to two different types of stencils and show a good match. This good match can also be taken from the corresponding images of Figure 9 relating to the second scenario 196.

When the stencil shrinkage (in x-direction and in y-direction) does not match with panel shrinkage, the position of the cavity 108 will shift away from the stencil aperture, i.e. from the corresponding ball passage 124. Hence, Figure 8 and Figure 9 indicate that an increase of a stencil opening leads, in combination with a reduced stencil thickness, to a better shrinkage behavior. By an increase of the stencil aperture, it may be possible to mitigate or even eliminate stencil match panel shrinkage issues.

Figure 10 and Figure 11 illustrate diagrams 200, 210 indicating target ranges of solder balls 114 applied to a component carrier structure 100 according to exemplary embodiments of the invention.

Diagram 200 of Figure 10 has an abscissa 202 along which a stencil thickness is plotted. Along ordinates 204, 206 a maximum offset (ordinate 204) and an alignment offset (ordinate 206) are plotted. A preferred range of parameters is shown in Figure 10 with reference sign 208. All measures are given in micrometers.

Diagram 210 of Figure 11 has an abscissa 212 along which a stencil opening is plotted. Along ordinates 204, 206 the maximum offset (ordinate 204) and the alignment offset (ordinate 206) are plotted. A preferred range of parameters is shown in Figure 11 with reference sign 218. All measures are given in micrometers.

A preferred stencil opening range may be defined as follows: Ball size + stencil hole accuracy (for instance 0.35 pm) + ball accuracy (for instance 0.3 pm) < stencil opening < design pitch (i.e. pad to pad center minimum distance) - ball accuracy (for example 0.35 pm) - stencil accuracy (for instance 0.3 pm).

The above described design rules for constructing the stencil may show an improved performance on printing maximum offset. In view of an alignment offset limitation being at a rate below value, it may be possible to compensate this by an opening increase (for example to 78 pm) to increase the alignment offset limitation.

It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also ele- ments described in association with different embodiments may be combined.

It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Implementation of the invention is not limited to the preferred embodiments shown in the figures and described above. Instead, a multiplicity of var- iants are possible which use the solutions shown and the principle according to the invention even in the case of fundamentally different embodiments.

Claims

Claims:

1. Component carrier structure (100), wherein the component carrier structure (100) comprises: a stack (102) comprising at least one electrically conductive layer structure (104) and at least one electrically insulating layer structure (106); at least one cavity (108), opening on one of external surfaces (110) of the component carrier structure (100); and flux material (112), at least partially filling said at least one cavity (108); wherein at least one solder ball (114) is provided, said at least one solder ball (114) being at least partially embedded in said at least one cavity (108) and said flux material (112).

2. Component carrier structure (100) according to claim 1, wherein said at least one cavity (108) opening on one of the external surfaces (110) of the component carrier structure (100) defines an external profile (116) by an intersection of the at least one cavity (108) with the respective external surface (110) of the component carrier structure (100), wherein said at least one solder ball (114) abuts against said external profile (116).

3. Component carrier structure (100) according to claim 2, wherein from the plan view of the respective external surface (110) of the component carrier structure (100), the at least one solder ball (114) is positioned to exceed the respective external profile (116) of the at least one cavity (108), wherein the ratio between a maximum exceeding measure 01 and a diameter Bl of said at least one solder ball (114) is within a range from 6.5% to 37.5%, particularly from 10% to 17%.

4. Component carrier structure (100) according to any of claims 1 to 3, wherein said at least one solder ball (114) is embedded in said at least one cavity (108) in accordance with an embedding measure B6 defined by a maximum measure between a bottom profile of the embedded at least one solder ball (114) and the respective external surface (110) of the component carrier structure (100), wherein the ratio of said maximum measure and a diameter Bl of said at least one solder ball (114) is within a range from 1.6% to 24%, particularly from 12.7% to 20.5%.

5. Component carrier structure (100) according to claims 3 and 4, wherein said maximum exceeding measure 01, said embedding measure B6, and said diameter Bl of said at least one solder ball (114) are dimensioned according to the following formula:

6. Component carrier structure (100) according to any of claims 1 to 5, wherein a plurality of solder balls (114) are embedded in respective cavities (108) each having the opening on one of the external surfaces (110), in particular wherein the majority of the solder balls (114), preferably at least 80% of the solder balls (114), abut against the external profile (116) of the respective cavity (108), more particularly wherein the majority of solder balls (114), preferably at least 80% of the solder balls (114), abutting against the external profile (116) of the respective cavity (108) abut against the respective cavity (108) in the same direction of the external profile (116) of the respective cavity (108) in a plan view.

7. Component carrier structure (100) according any of claims 1 to 6, wherein a diameter Bl of said at least one solder ball (114) is within a range from 5 pm to 300 pm, particularly from 40 pm to 100 pm.

8. Component carrier structure (100) according any of claims 1 to 7, configured as panel, array, pre-form of component carrier, or readily manufactured component carrier, in particular a printed circuit board or an integrated circuit substrate.

9. An apparatus (120) to connect at least one solder ball (114) with a component carrier structure (100), the component carrier structure (100) comprising a stack (102) comprising at least one electrically conductive layer structure (104) and at least one electrically insulating layer structure (106), at least one cavity (108) opening on one of external surfaces (110) of the component carrier structure (100), and flux material (112) at least partially filling said cavity (108), said apparatus (120) comprising a ball placement stencil (122) comprising at least one ball passage (124), and being configured to allow the at least one solder ball (114) to fall toward the at least one cavity (108) and the flux material (112) when said at least one ball passage (124) is at least partially vertically aligned with the respective cavity (108), wherein the apparatus (120) is configured so that when the stencil (122) is in its working position with respect to the component carrier structure (100), the at least one solder ball (114) is pushed to be entirely at or below an upper surface (164) of the stencil (122), wherein a distance B3+B4 between said upper surface (164) of the stencil (122) and the respective external surface (110) of the component carrier structure (100) is lower than a diameter Bl of the at least one solder ball (114), so that the at least one solder ball (114) is at least partially embedded in said at least one cavity (108) and said flux material (112).

10. An apparatus (120) according to claim 9, wherein the distance B3+B4 between said upper surface (164) of the stencil (122) and the respective external surface (110) of the component carrier structure (100) is configured so that said at least one solder ball (114) is embedded in said at least one cavity (108) in accordance with an embedding measure B6 defined by a maximum measure between a bottom profile of the embedded at least one solder ball (114) and the respective external surface (110) of the component carrier structure (100), wherein the ratio of said maximum measure B6 and a diameter Bl of said at least one solder ball (114) is within the range from 1.6% to 24%, particularly from 12.7% to 20.5%.

11. An apparatus (120) according to claim 9 or 10, wherein the stencil (122) comprises a planar plate (126) comprising said at least one ball passage (124) and a spacing device (128) in contact with the respective external surface (110) of the component carrier structure (100) when the stencil (122) is on its working position with respect to the component carrier structure (100).

12. An apparatus (120) according to claim 11, wherein a thickness B3 of the planar plate (126) is smaller than half of the diameter Bl of the at least one solder ball (114).

13. An apparatus (120) according to claim 12, wherein said at least one cavity (108) opening on one of the external surfaces (110) of the component carrier structure (100) defines an external profile (116) by an intersection of the at least one cavity (108) with the respective external surface (110) of the component carrier structure (100), wherein the external profile (116) of the at least one cavity (108) is circular with a cavity diameter B2, and when the at least one ball passage (124) contacts at a contact point (130) the at least one solder ball (114) on the opposite side of an abutment point of the at least one solder ball (114) with the external profile (116) of the respective cavity (108), a distance B5 between said contact point (130) and the external profile (116) of the respective cavity (108) opposite to said abutment point corresponds to the following formula:

₅₅ > B2 - (Bl - 01 - 02) + (B7 - B2) where 02 is a maximum exceeding measure of the at least one solder ball (114) exceeding said contact point (130), wherein 01 is a maximum exceeding measure of the at least one solder ball (114) exceeding the respective external profile (116) of the at least one cavity (108), and B7 is an opening width of the stencil (122), wherein in particular the external profile (116) of the at least one cavity (108) is circular with a cavity diameter B2, and when the at least one ball passage (124) contacts at a contact point (130) the at least one solder ball (114) on the opposite side of an abutment point of the at least one solder ball (114) with the external profile (116) of the respective cavity (108), B5 is a distance between said contact point (130) and the external profile (116) of the respective cavity (108) opposite to said abutment point, wherein the ratio of said distance B5 and the diameter Bl of the at least one solder ball (114) is within a range from 26% to 32.5%.

14. An apparatus (120) according to any of claims 9 to 13, wherein said apparatus (120) is configured to push the at least one solder ball (114) entirely at or below the upper surface (164) of the stencil (122) by a brush device (132) acting on an upper surface of the stencil (122).

15. A method of connecting at least one solder ball (114) with a component carrier structure (100), the method comprising: providing the component carrier structure (100) comprising a stack (102) comprising at least one electrically conductive layer structure (104) and at least one electrically insulating layer structure (106), at least one cavity (108) opening on one of external surfaces (110) of the component carrier structure (100), and flux material (112) at least partially filling said at least one cavity (108); operating a ball placement stencil (122) comprising at least one ball passage (124) for allowing the at least one solder ball (114) to fall toward the at least one cavity (108) and the flux material (112) when said at least one ball passage (124) is at least partially vertically aligned with the respective cavity (108); pushing the at least one solder ball (114) to be entirely at or below an upper surface of the stencil (122) when the stencil (122) is in its working position with respect to the component carrier structure (100); and adjusting a distance B3 + B4 between said upper surface of the stencil (122) and the respective external surface (110) of the component carrier structure (100) to be lower than a diameter Bl of the at least one solder ball (114), so that the at least one solder ball (114) is at least partially embedded in said at least one cavity (108) and said flux material (112).