RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No. 20201058818.8 filed on Jun. 9, 2020, entitled “RESIN FLOW RESTRICTION PROCESS AND STRUCTURE”, which is hereby incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present application relates generally to printed circuit boards, and more particularly to a resin flow restriction process and structure.

BACKGROUND

A printed circuit board (PCB) mechanically supports and electrically connects electronic components using conductive traces, pads and other features etched from electrically conductive sheets, such as copper sheets, laminated onto a non-conductive substrate. Multi-layered printed circuit boards are formed by stacking and laminating multiple such etched conductive sheet/non-conductive substrates. Conductors on different layers are interconnected with plated-through holes called vias.

A PCB includes a plurality of stacked layers, the layers are made of alternating non-conductive layers and conductive layers. The non-conductive layers can be made of prepreg or base material, that is part of a core structure, or simply core. Prepreg is a fibrous reinforcement material impregnated or coated with a resin binder and consolidated and partially cured to an intermediate stage semi-solid product. Prepreg is used as an adhesive layer to bond discrete layers of multiplayer PCB construction, where a multilayer PCB consists of alternative layers of conductors and base materials bonded together, including at least one internal conductive layer. A base material is a fully cured organic or inorganic material used to support a pattern of conductor material. A core is a metal clad base material where the base material has integral metal conductor material on one or both sides. A laminated stack is formed by stacking multiple core structures with intervening prepreg and then laminating the stack to fully cure the prepreg and bond the adjacent layers together. A via can then be formed by drilling a hole through the laminated stack and plating the wall of the hole with electrically conductive material, such as copper. The resulting plating interconnects the conductive layers in the laminated stack.

In conductive paste connected PCBs, cores are prepared separately and then electrically connected by conductive past and bonded together by prepreg through a lamination cycle. For pin insertion or component surface mount technology (“SMT”), there must be a resin free opening. To create a resin free opening in sequential lamination, it is common to use pre-cut low or no flow prepreg and control the resin flow as it is related to prepreg thickness, resin content, lamination pressure and lamination temperature. Due to design restrictions, the opening must be prepared in some cores. Therefore, improvements are desirable.

SUMMARY

In a first aspect of the present invention, a printed circuit board includes a first and second core. The first core has a first conductive layer, a first non-conductive layer, a first copper layer and a first opening. The first core also has a first solder mask connected to the first copper layer and a first FR4 laminate bonded to the first solder mask. The second core has a second conductive layer, a second non-conductive layer, a second copper layer and a second opening. The second core also has a second solder mask connected to the second copper layer and a second FR4 laminate bonded to the second solder mask. A prepreg layer is between the first copper layer and the second copper layer but not between the first FR4 laminate and the second FR4 laminate.

In a second aspect of the present invention, a method of manufacturing a printed circuit board includes adding a first solder mask to a first copper layer of a first core having a first opening; bonding a first FR4 laminate to the first solder mask; adding a second solder mask to a second copper layer of a second core having a second opening; bonding a second FR4 laminate to the second solder mask; mating the first core to the second core such that the first FR4 laminate is opposite the second FR4 laminate and the first opening and the second opening line up; adding a prepreg resin between the first copper layer and the second copper layer but not between the first FR4 laminate and the second FR4 laminate; and laminating the first core to the second core, wherein the first FR4 laminate and the second FR4 laminate reduce the prepreg resin flowing into the first and second openings.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features that are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

