CN110785003A - Stepped multi-layer PCB structure and preparation method thereof - Google Patents

Abstract

The invention relates to the technology of electronic assembly and semiconductor micro-assembly, in particular to a stepped multi-layer PCB structure and a preparation method thereof, wherein the PCB structure comprises a plurality of PCBs, connecting through holes are arranged on the PCBs, and two adjacent PCBs are connected through viscose glue and are stepped; the connecting through holes between two adjacent steps are aligned, a conductor penetrates through the connecting through holes to realize the electrical connection between the two PCBs, the wiring between the two adjacent PCBs is staggered and is designed with shielding measures, and the PCB adjacent to the welding position of the metal lead is provided with a perforation auxiliary hole; the multilayer stepped PCB structure can obtain good step shape, avoids the bonding pad from being polluted and has higher yield; meanwhile, the number of layers of the PCB of each step is greatly reduced compared with that of the PCB of the whole hot pressing mode, the plate opening and processing cost is also obviously reduced, and the processing period is obviously shortened.

Description

Stepped multi-layer PCB structure and preparation method thereof

Technical Field

The invention relates to electronic assembly and semiconductor micro-assembly technology, in particular to a stepped multi-layer PCB structure and a preparation method thereof.

Background

For the wire bonding between the bare chip and the circuit board, when the chip bonding points are densely arranged in multiple rows, the bonding wires need to be arranged in multiple layers, and the bonding pads on the circuit board side need to be arranged in different heights so as to prevent the bonding wires from being lapped, so that a stepped multilayer board is needed, as shown in fig. 1.

The stepped multilayer board can be realized by ceramic-based technologies such as HTCC, LTCC and the like, but has high cost and long period, and is not beneficial to rapid iteration in the research and development process. Compared with the prior art, the cost can be obviously reduced by adopting the multilayer PCB technology, but the yield is very low and even the whole batch of PCB can be scrapped, because the multilayer PCB is realized by adopting the cross-stacking hot-pressing technology of the double-sided copper-clad core board and the thermoplastic prepreg as shown in figure 2. Resin seeped from the prepreg during hot pressing overflows the step edges and flows to pollute the bonding pad, and the step shape is irregular (for a non-step PCB, the part polluted by the resin can be removed through machining after hot pressing, but the step PCB cannot be used in the way), so that the yield is low. Especially, in the case of a multi-layer PCB having blind holes 3, the above problem is more serious because of the need of performing hot pressing many times.

Disclosure of Invention

In order to solve the problem of low yield caused by resin overflow pollution in the manufacturing process of a stepped multilayer PCB, a stepped multilayer PCB structure is realized through a new technical path, so that the influence of resin overflow is eliminated, the cost is reduced, and the manufacturing period is shortened; the connecting through holes between two adjacent steps are aligned, and a conductor penetrates through the connecting through holes to realize the electric connection between the two PCB boards.

As an implementation mode, the electrical connection mode between the two PCB boards is implemented as follows: and the metal lead penetrates through the connecting through holes of the two PCBs, and two ends of the metal lead are welded on the surfaces of the PCBs.

As another implementation manner, the electrical connection between the two PCB boards is implemented as follows: and a metal screw passes through the connecting through holes of the two PCB boards, the other end of the metal screw is screwed and fixed by a metal nut, and a screw head and the nut of the metal screw are respectively contacted with the bonding pads on the two PCB boards.

Furthermore, the wiring between two adjacent PCB boards is staggered and designed with shielding measures.

Furthermore, a perforation auxiliary hole is arranged on the PCB adjacent to the welding position of the metal lead.

The invention provides a preparation method of a stepped multilayer PCB structure, which comprises the following steps:

the method comprises the following steps of preparing a PCB by adopting a double-sided copper-clad core board and a thermoplastic prepreg cross-stacking hot-pressing technology, wherein in the preparation process, a through hole for connection is formed in the PCB;

and obtaining regular edges by machining after hot pressing;

the PCB boards are stacked together, the edges of the PCB boards are staggered step by step to form an expected step-shaped structure, the PCB boards are fixed by adopting an adhesive way,

and aligning the connecting through holes between the two adjacent PCB boards, enabling the metal lead to penetrate through the two PCB boards, and respectively welding two ends of the metal lead to the surfaces of the two PCB boards.

The multilayer stepped PCB structure can obtain good step shape, avoids the bonding pad from being polluted and has higher yield; meanwhile, the number of layers of the PCB with each step is greatly reduced compared with that of the PCB with the whole hot pressing mode, the edition opening (the PCB with each step can be jointed) and processing cost are also obviously reduced, and the processing period is obviously shortened.

Drawings

FIG. 1 is a schematic view of a prior art stepped multi-layer panel;

FIG. 2 is a diagram illustrating a prior art technique for low yield and even a batch reject;

FIG. 3 is a schematic diagram of a multi-layer stepped PCB structure of the present invention;

the copper-clad core board comprises a copper-clad core board 1, a copper-clad core board 2, a prepreg 3, a blind hole 4, an adhesive 5 and a board threading.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a stepped multilayer PCB structure and a preparation method thereof, wherein the PCB structure comprises a plurality of PCBs, connecting through holes are formed in the PCBs, and two adjacent PCBs are connected through viscose glue and are stepped; the connecting through holes between two adjacent steps are aligned, and a conductor penetrates through the connecting through holes to realize the electric connection between the two PCB boards; the PCB comprises a copper-clad core board 1 and a prepreg 2.

The existing method adopts a mode of simultaneously stacking and hot-pressing all board layers, and is actually a multi-layer circuit board manufacturing process which is universal in the industry if the existence of step edges is not considered, so that the interconnection among the board layers can be realized through a conventional mode of drilling through holes and then electroplating.

However, in the invention, the steps are realized by gluing, the interconnection between the plate layers can not be realized by adopting a conventional mode of drilling through holes and then electroplating under the existing conventional technical stock, according to the test result, the interconnection is realized by adopting a mode of threading and welding between the plates, the interconnection between the plate layers can not be realized by adopting a mode of drilling through holes and then electroplating on the basis that people can glue the steps, through process innovation or existing process improvement, the interconnection between the plate layers can be realized by adopting a mode of drilling through holes and then electroplating, the invention provides the following two plate interconnection implementation modes:

as an implementation manner, as shown in fig. 3, the electrical connection between the two PCB boards is implemented as follows: penetrating the metal lead through the connecting through holes of the two PCBs, and welding two ends of the metal lead on the surfaces of the PCBs;

as another implementation manner, the electrical connection between the two PCB boards is implemented as follows: and a metal screw passes through the connecting through holes of the two PCB boards, the other end of the metal screw is screwed and fixed by a metal nut, and a screw head and the nut of the metal screw are respectively contacted with the bonding pads on the two PCB boards.

Furthermore, the wiring between two adjacent PCB boards is staggered and designed with shielding measures.

Furthermore, a perforation auxiliary hole is formed in the PCB adjacent to the welding position of the metal lead, the auxiliary hole is convenient for threading and welding, and the hole formed in the PCB can be understood as a round hole, so that a welding tool can extend into the hole.

The invention provides a preparation method of a stepped multilayer PCB structure, which comprises the following steps:

the method comprises the following steps of preparing a PCB by adopting a double-sided copper-clad core board and a thermoplastic prepreg cross-stacking hot-pressing technology, wherein in the preparation process, a through hole for connection is formed in the PCB; the manufacturing process of the PCB has no special points compared with the common PCB on the market, but the design of each board needs to be considered (including shielding measures for each board, mutual staggering on wiring and the like, and the purpose is to ensure that the boards can not mutually influence after being overlapped);

and obtaining regular edges by machining after hot pressing;

the PCB boards are stacked together, the edges of the PCB boards are staggered step by step to form an expected step-shaped structure, and the PCB boards are fixed in an adhesive mode; the plates are fixed in an adhesive mode, the adopted adhesive has low fluidity, and cannot overflow out of the plates to cause pollution to the surfaces of the steps (the surfaces of the steps are usually provided with bonding pads and sensitive to pollution), and in addition, the vertical surfaces at the steps are in regular shapes obtained by machining, so that the steps with good shapes and cleanness can be obtained;

and aligning the connecting through holes between the two adjacent PCB boards, enabling the metal lead to penetrate through the two PCB boards, and respectively welding two ends of the metal lead on the surfaces of the two PCB boards so as to realize the electrical interconnection between the two boards.

Further, the mechanical processing of the embodiment is milling; regular step edges (namely circuit board edges) are obtained through a machining mode, glue is prevented from overflowing from the boards in the gluing and stacking process, and good step morphology can be obtained.

The preparation of each above PCB, compare with current mode, though all cross the hot pressing of piling up of two-sided copper core board and thermoplasticity prepreg, but it is fixed through sticky but prepreg hot pressing realization between different ladders, and sticky going on after the hot pressing, be the step of establishing ties, each other does not influence, thereby can effectively control the flow of viscose, avoid it to spill over the step and cause the pollution, and among the current mode, the hot pressing between each intralamellar hot pressing of same ladder and the hot pressing between the ladder are gone on simultaneously, very easily consider one another, lead to oozing uncontrollably the step that overflows of prepreg resin between the ladder, lead to whole board to scrap.

Compared with the prior art, the PCB structure of the invention has the following characteristics:

1) breaking the whole into parts, decomposing the existing stepped multi-layer PCB with high layer number into a plurality of PCBs with lower layer number, respectively manufacturing, and then using adhesive to stack;

2) the whole division into parts is based on the distribution of steps, namely the plate layers at the same step are divided on the same plate, and the plate layers at different steps are not divided on the same plate;

3) therefore, regular step edges (namely circuit board edges) are obtained in a machining mode, glue is prevented from overflowing from the boards in the gluing and stacking process, and good step morphology can be obtained.

The cost and cycle ratio of the stepped multi-layer PCB structure realized by the integral hot pressing method and the method of the present invention are shown in table 1.

TABLE 1

Technical path	Cost of opening a plate	Cost of processing	Typical cycle of fabrication	Yield of
					Integral hot-pressing mode	1 ten thousand yuan or more	About 7300 yuan	45 days	8％
Mode for the invention	1000 Yuan	397 yuan	20 days	90％

The comparison of the table shows that the preparation method of the invention is superior to the PCB board produced by adopting the integral hot pressing mode in the aspects of processing cost, preparation period and product yield.

In the description of the present invention, it is to be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "other end", "upper", "one side", "top", "inner", "outer", "front", "center", "both ends", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "disposed," "connected," "fixed," "rotated," and the like are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; the terms may be directly connected or indirectly connected through an intermediate, and may be communication between two elements or interaction relationship between two elements, unless otherwise specifically limited, and the specific meaning of the terms in the present invention will be understood by those skilled in the art according to specific situations.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (7)

1. A stepped multilayer PCB structure comprises a plurality of PCB boards, and is characterized in that connecting through holes are formed in the PCB boards, and two adjacent PCB boards are connected through viscose glue and are stepped; the connecting through holes between two adjacent steps are aligned, and a conductor penetrates through the connecting through holes to realize the electric connection between the two PCB boards.

2. The stepped multi-layer PCB structure of claim 1, wherein the electrical connection between two PCBs is achieved by: and the metal lead penetrates through the connecting through holes of the two PCBs, and two ends of the metal lead are welded on the surfaces of the PCBs.

3. The stepped multi-layer PCB structure of claim 1, wherein the electrical connection between two PCBs is achieved by: and a metal screw passes through the connecting through holes of the two PCB boards, the other end of the metal screw is screwed and fixed by a metal nut, and a screw head and the nut of the metal screw are respectively contacted with the bonding pads on the two PCB boards.

4. The stepped, multi-layer PCB structure of claim 1, wherein the routing between adjacent PCBs is staggered and shielded.

5. The stepped, multi-layer PCB structure of claim 1, wherein a perforation aid hole is provided in the PCB adjacent to the metal lead bonding location.

6. A method for preparing a stepped multi-layer PCB structure is characterized by comprising the following steps:

the method comprises the following steps of preparing a PCB by adopting a double-sided copper-clad core board and a thermoplastic prepreg cross-stacking hot-pressing technology, wherein in the preparation process, a through hole for connection is formed in the PCB;

and obtaining regular edges by machining after hot pressing;

the PCB boards are stacked together, the edges of the PCB boards are staggered step by step to form an expected step-shaped structure, the PCB boards are fixed by adopting an adhesive way,

and aligning the connecting through holes between the two adjacent PCB boards, enabling the metal lead to penetrate through the two PCB boards, and respectively welding two ends of the metal lead to the surfaces of the two PCB boards.

7. The method of claim 6, wherein the machining is milling.

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