DE4326104A1 - Electrical assembly - Google Patents

Abstract

In the case of an electrical assembly, a plurality of printed circuit boards, which are preferably provided with conductor tracks on both sides, run parallel and are connected to one another with the aid of solder points.

Description

The invention is based on an electrical assembly the genus of the main claim.

To realize electrical circuits electrical components arranged on printed circuit boards that are attached to wear conductor tracks on at least one surface. At complicated circuits with many conductor tracks and many Conductor crossings it may be necessary To use multi-layer printed circuit boards. These are made by laminating a corresponding number Copper layers made with insulating intermediate layers. The inner layers are structured before Laminating process required. About the elaborate lamination In addition, the well-known multilayer printed circuit boards Disadvantage that plated through holes only through complex Processes can be made. This applies especially for vias, not all Capture trace layers. They are also expensive Materials for the production of the known Multi-layer circuit boards required.  

There are also known modules designed as modules that are designed for mounting on a larger circuit board and in turn contain one or more circuit boards.

The object of the present invention is both improve the aforementioned assemblies. In particular, each should depending on the application, a high one Component density and / or a variety of themselves crossing ladders may be possible without the disadvantages of known multilayer printed circuit boards.

The electrical assembly according to the invention is thereby characterized that several, preferably on both sides PCBs with conductor tracks run parallel and are connected to each other with the help of solder points.

These solder points can be created by soldering a ball grid Arrays (also called "Solder Grid Array") on a base arise.

To create the individual soldering points, they are wettable Areas on the mutually facing sides of the connecting circuit boards required. on the one Printed circuit board a ball grid array is created by the fact that in a suitable way solder balls on the conductor track pads applied: A possible method for this is in the Patent application P 43 16 007.7 described by the applicant. The opposite surfaces (landing surfaces) of the others Printed circuit boards are made with solder paste or with a flux provided if the metal used is not anyway a flow of the solder in the subsequent reflow process allowed. In the subsequent reflow process, the Melted solder balls and by wetting the Opposing conductor pads become solder points educated.  

The shape of the resulting solder points depends, among other things the shape of the track pads. The distance between the Printed circuit boards, i.e. the height of the solder points, is at appropriate choice of parameters, for example 0.6 mm.

These and other suitable methods of connecting Printed circuit boards using soldering points can be used to manufacture Assemblies according to the invention are used.

An advantageous embodiment of the invention exists in that at least two circuit boards in one by the Solder points due to each other and that the Conductor tracks of the superimposed circuit boards including vias and electrical Connections by soldering a multilayer printed circuit board form.

Such an assembly according to the invention has the advantage that the simplest PCB base materials, such as for example XPC, can be used. Also are Vias can be produced in a simple manner including those that are not all circuit boards penetrate, namely so-called "blind vias" and "buried vias ".

Compared to assemblies with the known Multilayer printed circuit boards have these according to the invention Assembly the advantage that a slight offset of the individual conductor track layers less critical than in Standard multilayer boards is because of that for joining Solder Ball soldering process used a self-adjusting Has effect. Furthermore, in the invention Process the area percentage of more than two layers Conductor tracks required, adapted to the respective need become. It is not necessary, as with the known ones Multi-layer printed circuit boards always the whole for one  Assembly required PCB area with the maximum to provide the required number of layers (partial Multilayer), which significantly reduces costs in individual cases can be.

A further development of this embodiment of the invention is that on one of the other circuit board facing side of at least one circuit board components are arranged. This makes it inexpensive Realizability of so-called "buried" components possible, which are arranged between the circuit boards. This is often necessary, for example, for Blocking capacitors to get short leads. To the Components include capacitors, packaged and unpackaged semiconductors and also printed resistors.

Another embodiment of the invention is that another circuit board between two circuit boards is arranged, which is a recess for on a has adjacent components arranged components. This makes it possible to use components that are not one have a particularly low height within the assembly to accommodate. Depending on the requirements in detail a particularly compact assembly can be achieved that the circuit boards and the other circuit boards are arranged alternately one above the other.

This embodiment also enables compact assemblies with a large number of possible components on the area occupied by the assembly Basic circuit board. In particular, modules can be more simple Provided way with several component-bearing floors be, even on the top and bottom of the Printed circuit board components can be arranged.  

In the assembly according to the invention it can be provided that that the circuit boards and possibly the other Printed circuit boards have the same external dimensions or that the dimensions of the circuit boards are different in size.

Another development of the assembly according to the invention is that the connecting the circuit boards Soldering points are arranged in several rows, the Soldering points are staggered from row to row. This allows the soldering points to be honeycomb-shaped. Thus, a denser packing than in the circular shape can be achieved.

An advantageous method of making a Assembly according to the invention is that on the each side facing the other circuit board Printed circuit boards for the soldering points provided with solder wettable metallic areas are produced that the metallic areas on both sides with a solder paste are covered, the amount of solder paste over the size of the metallic area on one side is that this will melt during the subsequent melting Solder paste due to the surface tension of the solder on the metallic areas each substantially spherical pulls together that on the solidified balls with Solder paste printed areas of the other circuit board be, the amount of the solder paste order on the dimensioned metallic areas of the other circuit board is that the common height of the ball and the Solder paste order exceeds the height of the components and the soldering points that form when heated again train about barrel-shaped.

It is preferably provided in this method that the Apply solder paste to each ball Areas of the other circuit board are annular  is. As a result, the balls are on with the solder paste application the other circuit board at the start of the reflow process a larger touch range.

Embodiments of the invention are in the drawing represented with several figures and in the following Description explained in more detail. It shows:

Fig. 1 shows a cross section through an inventive assembly prior to soldering which connects two boards to each other,

Fig. 2 shows a cross section of the same assembly after the soldering process according to the invention,

Fig. 3 shows a detail of inventive assembly,

Fig. 4 excerpts from further assemblies according to the invention and

Fig. 5 to Fig. 11 show further exemplary embodiments, also shown as cross-sections.

In the embodiment shown in FIGS. 1 and 2, it is essential to obtain four connection levels for a circuit, not shown in detail. For this purpose, two printed circuit boards 1 , 2 are each provided on both sides with conductor tracks, which are not shown in detail in FIGS. 1 and 2. Both the mechanical and the electrical connection of the two circuit boards is made by a large number of soldering points, which is known per se as a "ball grid array" or "solder grid array".

Prerequisites for the creation of the individual soldering points 3 are wettable areas on the mutually facing sides of the printed circuit boards 1 , 2 . These can be parts of already existing conductor tracks and plated-through holes or can be arranged specifically for connecting the printed circuit boards 1 , 2 . The method for producing the assembly shown in FIGS. 1 and 2 comprises, for example, the following steps:

• 1. Generation of solder balls 4 on the underside of the circuit board 2 ,
• 2. Application of solder paste points 5 to the top of the circuit board 1 ,
• 3. Positioning the printed circuit board 2 on the printed circuit board 1 such that the solder balls of the printed circuit board 2 each lie on their associated solder paste point on the printed circuit board 1 .
• 4. Reflow soldering.

If SMD components are provided on both sides of the double circuit board shown in FIG. 2, the assembly is manufactured, for example, as follows:

• 1. solder ball generation on the underside of the circuit board 2 ,
• 2. Solder paste screen printing on the top of the circuit board 2 ,
• 3. assembly of the SMD components in the solder paste on the top of the circuit board 2 ,
• 4. solder paste screen printing on the underside of the circuit board 1 ,
• 5. assembly of the SMD components in the solder paste on the underside of the circuit board 1 ,
• 6. reflow soldering of circuit board 1 ,
• 7. solder paste screen printing on the top of the circuit board 1 ,
• 8. Positioning the printed circuit board 2 on the printed circuit board 1 such that the solder balls of the printed circuit board 2 each lie on their associated solder paste point on the printed circuit board 1 .
• 9. Reflow soldering.

In this way, two simple (two-layer) Connected circuit boards, a Four-layer circuit board.

FIG. 3 shows a section of such a plate in order to explain different forms of vias. A through-contact 13 , which is produced using a method known per se, is located between a conductor track 11 on the upper side of the circuit board 2 and a conductor track 12 on the lower side of the circuit board 2 . Since this via does not go through the entire printed circuit board, ie does not connect all layers with one another, such a via is also called "blind via". A similar via 14 is located between the conductor tracks 15 and 16 on the upper and lower side of the printed circuit board 1 . A so-called buried via is obtained through a soldering point 17 . The invention can be extended in an analogous manner to more layers by appropriate arrangement of more circuit boards.

For the sake of miniaturization or for one It is to guarantee perfect electrical function necessary in many applications, all or certain electrical components in the shortest possible way Ways to connect. This applies, for example for a blocking capacitor close to an integrated one Circuit too. In certain cases it is therefore necessary such capacitors on inner layers to arrange. In the known multilayer printed circuit boards are such "buried" components only with large Effort realized.  

In the arrangement according to the invention, simple integration of such components is possible. It is particularly easy to integrate the components between the individual circuit boards if they are flatter than the soldering points used to connect the circuit boards. An example of this is shown in FIG. 4 a, wherein the buried component 18 can be a capacitor, for example.

FIG. 4b shows also as an example cross-section of a buried component 19, which has a greater height than the solder bumps caused by the distance between two printed circuit boards. Therefore, in the example shown in Fig. 4b, a further circuit board 20 is inserted, which has a recess 20 'for receiving the component 19 .

In the following explanations of the exemplary embodiments according to FIGS. 5 to 11, printed circuit boards, each consisting of a printed circuit board and printed conductors applied on both sides and bearing components, are referred to as floors. In order to increase the distance between two floors, printed circuit boards are also provided which are frame-shaped due to a recess in the interior and are therefore referred to below as frame elements.

Before the various exemplary embodiments are explained, the basic structure is described below. The first (i.e. the lowest) floor 21 ( FIG. 5) is based on a one-tier module, which, however, has no cap. The components 26 located on the upper side of the first floor 21 leave an edge zone free, on which there are landing areas for solder balls, onto which solder paste is printed immediately before the soldering process. The first frame element 22 is positioned with its solder balls in the solder paste on the first floor. During the later soldering process, the ball and solder paste merge on the landing surface to form a soldering point that is spherical to barrel-shaped. A frame element corresponds to the construction of a floor, but does not itself have any components, but rather the largest possible cutout 25 in the interior. The size of the recess is only limited by the structures of the frame element. Essentially, these are the landing areas for the solder balls on the second floor 23 on the upper side, and the solder balls for connection to the first floor and vias 24 on the underside.

In the soldered frame element, a soldering point on the top and one on the underside are electrically connected to one another with a via. This creates - as soon as necessary - a current-carrying path from the upper to the lower soldering point. The components 26 , which are arranged on the first floor 21 , protrude into the recess 25 of the frame element 22 .

Solder paste is again applied to the landing surfaces of the frame element 22 that has not yet been soldered, and the second tier 23 is positioned with its solder balls in the landing surfaces printed with solder paste. If more than two levels are to be realized, a corresponding number of frame elements and levels are alternately stacked and soldered onto one another.

If there are components 27 on the upper side of the top floor, a cap 28 is put on in order to protect the circuit and to create a possibility for automatic assembly. By means of further solder points 30, the assembly is shown in FIG. 5 connected to a base circuit board 31.

Compared to the embodiment according to FIG. 5, the embodiment according to FIG. 6 is designed by a further frame element 32 in such a way that further components 33 can be arranged on the main circuit board 30 below the assembly.

In the exemplary embodiments according to FIGS. 5 and 6, a cuboid shape of the assembly was assumed. However, other shapes are also possible within the scope of the invention, for example a pyramidal shape in which the next higher floor takes up a smaller area than the one below. Exemplary embodiments are shown in FIGS. 7 and 8. The area of the first floor 35 which is not occupied by a higher floor can be used to arrange high components 36 . In the embodiment according to FIG. 8, a further frame element 37 is additionally provided, so that the main circuit board 30 can carry components 33 below the assembly.

In the case of three-tier and multi-tier structures, the cuboid shape and the pyramidal shape can also be combined, for example, in that the two lower floors have the same external measurements, while the third is smaller. For example, in the exemplary embodiment according to FIG. 9, only part of the surface of the second floor is covered by a cap 38 . The vacated area of the second floor 23 is used for higher components 39 or for components with convection cooling.

Fig. 10 shows an assembly according to the invention, in which the tier structure is realized without frame elements. First, second and third floors 41 , 42 , 43 each carry components 44 . The clear height between the floors in this embodiment is approximately 0.6 mm, so that correspondingly flat components are required, for example integrated circuits in flip-chip mounting and printed resistors. Mixed forms with floors without and with frame elements are also possible within the scope of the invention.

A circuit board 45 forms the end of the component shown in FIG. 10.

In the exemplary embodiments shown in FIGS. 5 to 10, the components are located on the top of the individual printed circuit boards. In contrast, FIG. 11 illustrates an embodiment in which the circuit board 46, which is the top level, is equipped on the bottom with components 47th Another frame element 48 creates a sufficient distance from the circuit board 23 . The remaining levels and frame elements correspond to those of the embodiment shown in FIG. 6. Since the components 47 on the top floor are arranged on the underside of the printed circuit board 46 , the printed circuit board 46 simultaneously forms a closure or a cover.

Claims (11)

1. Electrical assembly, characterized in that several, preferably provided on both sides with conductor tracks, circuit boards ( 1 , 2 ; 21 , 23 ; 41 , 42 , 43 , 45 ) run in parallel and are connected to one another with the aid of soldering points ( 3 ) . 2. An assembly according to claim 1, characterized in that at least two printed circuit boards ( 1 , 2 ) lie one on top of the other at a distance due to the soldering points ( 3 ), and in that the conductor tracks ( 11 , 12 , 15 , 16 ) of the printed circuit boards ( 1 , 2 ) including vias ( 13 , 14 ) and electrical connections through solder points ( 17 ) form a multilayer printed circuit board. 3. Module according to claim 2, characterized in that on a side facing away from the other circuit board at least one circuit board components are arranged. 4. Module according to one of claims 2 or 3, characterized in that on one of the other circuit board ( 2 ) facing side at least one circuit board ( 1 ) components ( 18 ) are arranged. 5. Assembly according to one of the preceding claims, characterized in that between two circuit boards ( 1 , 2 ; 21 , 23 ) a further circuit board ( 20 ; 22 ) is arranged, which has a recess ( 20 '; 25 ) for on an adjacent circuit board ( 1 ; 21 ) arranged components ( 19 ; 26 ). 6. An assembly according to claim 5, characterized in that the circuit boards ( 21 , 23 ) and the further circuit boards ( 32 , 22 ) are arranged alternately one above the other. 7. Module according to one of the preceding claims, characterized in that the circuit boards ( 21 , 23 ) and optionally the further circuit boards ( 22 ) have the same external dimensions. 8. Module according to one of the preceding claims, characterized in that the dimensions of the circuit boards ( 23 , 35 ) are of different sizes. 9. Module according to one of the preceding claims, characterized in that the the printed circuit boards connecting solder points are arranged in several rows, where the solder points from row to row against each other are offset. 10. Method of manufacturing an assembly according to a of the preceding claims, characterized in that on the sides facing the other PCB of the printed circuit boards intended for the solder points with solder wettable metallic areas are produced that the metallic areas on both sides with a solder paste are covered, the amount of solder paste over the size of the metallic area on one side is that this will melt during the subsequent melting Solder paste due to the surface tension of the solder on the  metallic areas each substantially spherical pulls together that on the solidified balls with Solder paste printed areas of the other circuit board be, the amount of the solder paste order on the dimensioned metallic areas of the other circuit board is that the common height of the ball and the Solder paste order exceeds the height of the components and the soldering points that form when heated again train about barrel-shaped. 11. The method according to claim 10, characterized in that the solder paste application of the one ball assigned Areas of the other circuit board are annular is.