CN109103164B

CN109103164B - BGA (ball grid array) interconnection structure of LTCC (Low temperature Co-fired ceramic) substrate and implementation method

Info

Publication number: CN109103164B
Application number: CN201810685107.2A
Authority: CN
Inventors: 岳帅旗; 杨宇; 张继帆; 刘志辉; 徐洋
Original assignee: CETC 29 Research Institute
Current assignee: CETC 29 Research Institute
Priority date: 2018-06-28
Filing date: 2018-06-28
Publication date: 2020-09-29
Anticipated expiration: 2038-06-28
Also published as: CN109103164A

Abstract

The invention relates to the field of LTCC circuit substrate manufacturing, in particular to a BGA interconnection structure of an LTCC substrate and an implementation method. According to the invention, an external dielectric layer replacing a solder mask layer is arranged on the surface of the LTCC substrate needing BGA interconnection; utilizing an LTCC post-firing process to manufacture the BGA bonding pad on the outer surface of the external dielectric layer of the LTCC substrate; and arranging an external metalized through hole in the external dielectric layer corresponding to the BGA bonding pad.

Description

BGA (ball grid array) interconnection structure of LTCC (Low temperature Co-fired ceramic) substrate and implementation method

Technical Field

The invention relates to the field of LTCC circuit substrate manufacturing, in particular to a BGA interconnection structure of an LTCC substrate and an implementation method.

Background

With the continuous and deep miniaturization, multifunction and modularization, the LTCC-based multifunctional SIP packaging is rapidly developed, high-frequency and high-reliability vertical interconnection becomes a prominent problem restricting the application of the LTCC multifunctional SIP module, and a good solution is urgently needed.

Due to the characteristics of small space occupation, convenient assembly and the like, BGA is paid more and more attention in the high-frequency vertical interconnection assembly of LTCC. A0.5-20.0 GHz high-density broadband digital-analog mixed signal BGA vertical transmission scheme based on an LTCC substrate is designed in the article 'application of BGA in broadband radio frequency interconnection of a micro system' of Weiwei et al. Zhangsefan et al in the patent "high frequency vertical interconnect circuit based on modified BGA" optimizes the high frequency transmission and isolation characteristics by introducing solder rings around the BGA balls. Zhao Shao Wei et al invented a method for realizing high frequency transmission of an LTCC substrate and a PCB board in a BGA manner in a patent of a vertical interconnection structure and method between LTCC and PCB based on high frequency transmission. In the patent "a microwave LTCC substrate vertical interconnection structure" of Armada et al, an LTCC vertical interconnection structure based on BGA was invented. Li jiahui et al in a patent of PGA/BGA three-dimensional structure for component assembly and method of making the same, an interconnection between LTCC modules is achieved using a BGA. Wang dazzling et al invented a BGA vertical interconnection mode between LTCC boards that can realize Ku signal transmission in a "vertical interconnection transition structure for three-dimensional components".

Although various researches prove that the BGA is good in prospect when used for high-frequency vertical interconnection of the LTCC substrate, the reliability of interconnection is not well solved, and welding spot failure is easy to occur particularly under service conditions of high and low temperature impact, vibration impact and the like. The reasons for the failure of the BGA solder joints are mainly as follows: 1) thermal stress is introduced by thermal mismatch between the LTCC with the thermal expansion coefficient of 5-7 PPM and the PCB motherboard with the thermal expansion coefficient of 14-20 PPM; 2) positional deviations of LTCC substrate BGA pads introduce assembly residual stress. The thermal mismatch stress of the LTCC and the assembly mother board needs to give systematic consideration from the aspects of reliability requirement, service environment, structural design, thermal design and the like, the process is complex, or a high thermal expansion coefficient LTCC material system is developed to realize thermal matching with the assembly mother board, but the development cycle is very long. LTCC base plate BGA pad relative position deviation is because the shrinkage factor error of sintering process leads to, shrinkage factor error control level is 0.3% in the industry, and to high frequency BGA interconnection, because the requirement of large tracts of land ground connection, often need be at ground plane surface preparation solder mask, the position deviation between ground connection BGA pad and the signal BGA pad has been led to again, the position deviation between the LTCC base plate BGA pad has further been aggravated, can't with the accurate alignment between the BGA pad of assembly motherboard, great residual stress appears after the assembly.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the method or the structure eliminates the position deviation of an original LTCC substrate BGA bonding pad, so that the residual stress of assembly of the LTCC substrate and a motherboard BGA is reduced, and the highly reliable BGA vertical interconnection of the LTCC substrate is realized.

The technical scheme adopted by the invention is as follows:

a method for realizing a BGA interconnection structure of an LTCC substrate comprises the following steps:

arranging an external dielectric layer for replacing a solder mask on the surface of the LTCC substrate needing BGA interconnection;

utilizing an LTCC post-firing process to manufacture the BGA bonding pad on the outer surface of the external dielectric layer of the LTCC substrate;

and arranging external metalized through holes in the external dielectric layer corresponding to the positions of the BGA bonding pads.

Furthermore, the external metalized through hole is the same as the metalized through hole conductor of the original LTCC substrate, and the diameter of the external metalized through hole conductor is 0.05 mm-0.5 mm. The material of the external dielectric layer is the same as that of the original LTCC circuit medium, and the thickness of the external dielectric layer is 0.03 mm-0.3 mm.

Furthermore, the corresponding BGA pad position means that a BGA pad needs to be fabricated at the corresponding BGA pad position.

Furthermore, the external dielectric layer and the original LTCC substrate form a whole after being co-fired, and the whole is used as a new surface of the substrate.

Further, the post-firing process is to print conductor paste on the co-fired LTCC substrate, and form a film layer with a corresponding function after drying and sintering.

Furthermore, the BGA bonding pad manufacturing means that a conductor film layer is manufactured at the position of a BGA welding spot through a post-firing process; the BGA bonding pad comprises Ag/Pd or Pt/Au/Pd; the thickness range of the BGA bonding pad is 10-45 mu m.

Further, the method also comprises the step of implanting BGA solder balls on the BGA bonding pad.

The interconnection structure based on the method comprises an external dielectric layer, a BGA bonding pad and an external metalized through hole, wherein the BGA bonding pad is manufactured on the outer surface of the external dielectric layer of the LTCC substrate; the external dielectric layer is a dielectric layer which replaces a solder resist layer and is arranged on the surface of the LTCC substrate needing BGA interconnection; the BGA bonding pad is formed on the outer surface of the external connection medium layer through an LTCC post-firing process; the external metalized through hole is arranged in the external dielectric layer and corresponds to the BGA bonding pad.

Further, the structure also comprises a BGA welding ball planted on the BGA welding pad.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

the BGA interconnection structure can eliminate the pad position deviation caused by LTCC sintering shrinkage error, thereby reducing the residual stress of the substrate after BGA assembly and improving the reliability of BGA interconnection. The structure can be suitable for the verticality of high-frequency signals, and the implementation method is a mature process and is simple to operate.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 is a schematic cross-sectional view of a BGA structure of a conventional LTCC substrate.

Fig. 2 is a schematic view of ball mounting of a BGA pad of a conventional LTCC substrate.

FIG. 3 is a schematic diagram of an exemplary cross-section of an LTCC substrate after adding an external dielectric layer.

FIG. 4 is a schematic cross-sectional view of an embodiment of a BGA pad structure of an LTCC substrate of the present invention.

FIG. 5 is a schematic diagram of an embodiment of ball mounting on a BGA pad of an LTCC substrate according to the present invention.

FIG. 6 is a schematic diagram of another exemplary BGA structure of the LTCC substrate of the present invention.

Reference numerals:

c-substrate internal signal transmission line

e-vertical interconnect signal vias within substrate

L (lower case letter L) -large-area conductor pattern on upper surface of substrate

k-substrate upper surface signal transmission line

h-external dielectric layer of substrate, i external metallized through hole in external dielectric layer

1-FIG. 1 is a conventional LTCC substrate

2-Large area conductor pattern (ground layer) on the upper surface of the substrate

3-substrate internal vertical interconnection grounding hole

3' -vertical interconnection signal hole in substrate

4-substrate internal signal transmission line

5 respectively-large-area conductor patterns (ground layers) of the lower surface of the substrate

6-BGA Signal pads on the lower surface of the substrate, connected to the Signal holes 3

7-solder mask on substrate surface

8-hollowed out area of solder mask, this location is the pad of the grounded BGA.

Detailed Description

All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.

Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.

The implementation method of the invention comprises the following steps:

as shown in fig. 3, a conventional process is utilized, a novel structure LTCC circuit substrate a is manufactured through the conventional LTCC processes of punching, hole filling, printing, laminating, co-firing and the like, 2 is a substrate upper surface conductor film layer, 4 is a substrate internal signal line, 5 is a substrate internal large-area conductor pattern, 2, 4 and 5 are made of Ag or Au, the film thickness is 5-12 μm, the width and length of the signal line 4 are flexibly adjusted according to design requirements, and the dielectric thickness of the

conductor patterns

2 and 5 from 4 to large areas is designed according to electrical characteristic requirements. 3 is the inside perpendicular interconnection ground hole of base plate, and 3 'is the inside perpendicular interconnection signal hole of base plate, and 3' material are Ag or Au, and the through-hole can be adjusted according to the design demand is nimble between 0.08mm ~0.3 mm. 10 is a newly added external dielectric layer of the LTCC substrate, 11 is an external metalized through hole on the newly added external dielectric layer, and the position of the through hole corresponds to the position of the BGA bonding pad.

On the basis of the method, the method further comprises the step of planting balls on the novel high-precision BGA bonding pad by using a conventional BGA ball-planting process, wherein 13 is a solder ball as shown in figure 5. The method specifically comprises the following steps:

as shown in fig. 4, after printing LTCC on a substrate a, a conductive paste is fired, the material is PdAg or ptaudd, the position of the BGA pad on the printing screen is the same as the BGA position of the mounting motherboard, and the size of the pad is designed according to the BGA ball diameter matching design. And drying the substrate after printing, wherein the drying temperature is generally 80-120 ℃, and the drying time is 10-30 min. And after drying, post-baking the substrate to form a high-precision BGA bonding pad 12 on the lower surface of the LTCC substrate a, wherein the thickness of the film layer is 20-35 mu m. Solder mask is not made between the bonding pads, and the solder mask between the BGA balls is automatically realized by using the ceramic surface of the non-bonding pad area.

Fig. 2 is a schematic structural view of a conventional LTCC substrate 1 after being implanted with BGA solder balls 9 on its lower surface. 2. 3, 3', 4 and 5 are all made of conductors, and non-conductor areas in the substrate are all made of ceramic dielectrics.

Fig. 3 is a schematic diagram of a novel LTCC substrate a with a structure formed by adding an external dielectric layer on the lower surface, wherein 2 is a large-area conductor pattern on the upper surface of the substrate, 5 is a large-area conductor pattern inside the substrate, 3 is a vertical interconnection grounding hole inside the substrate, 4 is a signal transmission line inside the substrate, 3 'is a vertical interconnection signal hole inside the substrate, 2, 3', 4, and 5 are made of a conductor, and a non-conductor region inside the substrate is a ceramic medium. 10 is a newly added external dielectric layer, and 11 is an external metalized through hole on the newly added external dielectric layer.

Fig. 4 is a schematic structural view after the BGA pad 12 is formed on the lower surface of the new LTCC substrate a.

Fig. 5 is a schematic structural diagram of a new LTCC substrate a after the lower surface pads 12 are plated with BGA solder balls 13.

Fig. 6 shows another form of the novel BGA structure, wherein s is an LTCC substrate, L, b, d, and m are large-area conductor patterns inside the substrate, g is a metalized via hole on a newly added external dielectric layer, j is a BGA pad on the lower surface of the substrate, all the large-area patterns, signal lines, vertical interconnection grounding holes, and signal holes are made of conductors, and the non-conductor region is a ceramic dielectric.

The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.

Claims

1. A preparation method of a BGA interconnection structure of an LTCC substrate is characterized by comprising the following steps:

arranging an external dielectric layer for replacing a solder mask on the surface of the LTCC substrate needing BGA interconnection, wherein the external dielectric layer and the original LTCC substrate form a whole after being co-fired;

utilizing an LTCC post-firing process to manufacture the BGA bonding pad on the outer surface of the external dielectric layer of the LTCC substrate; forming a BGA bonding pad on the outer surface of an external dielectric layer after co-firing through printing, drying and sintering of conductor slurry, and using the BGA bonding pad as a new surface of an LTCC substrate;

2. The method of claim 1, wherein the circumscribed metalized via is the same as a metalized via conductor of an original LTCC substrate, and has a diameter of 0.05mm to 0.5 mm; the material of the external dielectric layer is the same as that of the original LTCC circuit medium, and the thickness of the external dielectric layer is 0.03 mm-0.3 mm.

3. The method of claim 1, wherein the corresponding BGA pad location is a location at which a BGA pad needs to be fabricated.

4. The method of claim 1, wherein the BGA pad fabrication is performed by post-firing conductive film layers at BGA solder joint locations; the BGA bonding pad comprises Ag/Pd or Pt/Au/Pd; the thickness range of the BGA bonding pad is 10-45 mu m.

5. The method of any one of claims 1 to 4, further comprising implanting BGA solder balls on the BGA pads.

6. The interconnect structure prepared by the method of claim 5, comprising an external dielectric layer, a BGA pad formed on an outer surface of the external dielectric layer of the LTCC substrate, and an external metallized via; the external dielectric layer is a dielectric layer which replaces a solder mask layer and is arranged on the surface of the LTCC substrate needing BGA interconnection, and the external dielectric layer and the original LTCC substrate form a whole after being co-fired; the BGA bonding pad is formed on the outer surface of the external dielectric layer through an LTCC post-firing process, namely the BGA bonding pad is formed on the outer surface of the co-fired external dielectric layer through printing, drying and sintering of conductor slurry and is used as a new surface of the LTCC substrate; the external metalized through hole is arranged in the external dielectric layer and corresponds to the BGA bonding pad.

7. The structure of claim 6 further comprising Ball Grid Array (BGA) solder balls on the BGA pads.