Method of manufacturing coreless substrate

The present invention generally relates to IC packaging, and more particularly to a method of manufacturing coreless substrates for IC packaging.

The IC packaging is for protecting dies and providing an interface for the communications between the dies and the external circuitry. As electronic devices are continuously driven for smaller dimension and lighter weight, IC packaging is also required to be even more compact and to have higher layout density. To meet these requirements, numerous new technologies of IC packaging are proposed.

Conventional substrates for IC packaging (hereinafter, packaging substrates) are fabricated by directly forming a wiring layer on a CCL (copper coated laminate) base which is made by pressing a copper foil onto a resin core layer. Due to the constraints of the vias (i.e., through holes) and the thickness of the copper foil, CCL-based packaging substrates cannot offer the thickness and layout density required by recent IC packaging applications.

Currently, a number of methods such as Build Up and Semi-Additive Process (SAP) have been utilized to increase the layout density by forming multiple wiring layers on both sides of a core layer of the packaging substrate. However, vias are still required in providing electrical connection between the wiring layers (i.e., interlayer connection) on the core layer's two sides and, therefore, signal interference is inevitable. Also, when only one side of the packaging substrate requires high layout density, using Build Up method adds unnecessary cost and substrate thickness by having multiple wiring layers on the other side of the core layer as well.

Therefore, to increase the layout density and the quality of the electrical signal for packaging substrates so as to meet market demands, the so-called coreless substrate is proposed, which removes the thick core layer and uses blind vias for interlayer connection. In addition, coreless substrate is actually a flexible printed circuit board (PCB) and it can be manufactured using conventional equipments for regular PCB. Therefore, coreless substrate allows manufacturers to make flexible PCBs without additional investment in purchasing equipments specifically for flexible PCBs.

The present invention provides a method for manufacturing coreless substrates. Basically, the method conducts the process of building up wiring layers to both sides of a base simultaneously. After wiring layers on both sides of the base are built, they are removed from the base to become two independent semi-products. The semi-products are then put through the subsequent processes to make them into two coreless substrates. This method not only achieves the fabrication of coreless substrates, but also can double the production capacity.

More specifically, the method first provides a base whose top and bottom sides are covered with metal layers respectively that are detachable from the base. From the two metal layers, the method then develops the bump-pad side or ball side wiring layers required by the coreless substrate simultaneously. The two metal layers along with their respective wiring layers are then separated from the base into two independent semi-products of the coreless substrate. The method then develops from the other sides of the two semi-products the laminate side wiring layers required by the coreless substrate. As such, two coreless substrates are manufactured with a single process.

The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.

FIG. 1 is a flow chart showing the processing steps of manufacturing coreless substrates according to the present invention.

FIG. 2 is a perspective diagram showing the base used to manufacture the coreless substrate according to an embodiment of the present invention.

FIG. 3A is a perspective diagram showing the result after Step S 10 of FIG. 1 .

FIG. 3B is a perspective diagram showing the result after Step S 12 of FIG. 1 .

FIG. 4A is a sectional diagram of FIG. 3B .

FIGS. 4B˜4C are sectional diagrams showing the results after Steps S 14 and S 16 of FIG. 1 , respectively.

FIGS. 5A-5D are sectional diagrams showing the result after the processing steps of FIG. 1 according to another embodiment of the present invention.

FIG. 1 shows a flow chart of the method for manufacturing coreless substrate according to the present invention. As shown in FIG. 1 , in Step S 10 , a base having detachable metal layers on both top and bottom sides are provided. As shown in FIG. 2 , an embodiment of the base has a hollow dielectric frame 10 with four side walls 10 a made of a dielectric material. Two metal layers 12 and 13 cover the top and bottom sides of the dielectric frame 10 , respectively. Each of the outer surfaces of the metal layers 12 and 13 is partitioned into a wiring area 12 a and a rim area 12 b surrounding the wiring area 12 a . The wiring area 12 a is where the wiring is formed and the rim area 12 b will be removed in subsequent steps. The width of the rim area 12 b is substantially conforming to the thickness of the side walls 10 a . The result of joining the metal layers 12 and 13 to the dielectric frame 10 is shown in FIG. 3A .

Then, in Step S 12 , wiring layers 16 and 17 are formed on the outer surfaces of the metal layers 12 and 13 , respectively. Each of the wiring layers 16 and 17 functions as the bump-pad side or ball-side wiring layer of a coreless substrate. Please note that each of the wiring layers 16 and 17 also contains wiring area 12 a and rim area 12 b . Similarly, the width of the rim area 12 b of either wiring layer 16 or 17 is substantially conforming to the thickness of the side walls 10 a , as shown in FIG. 3B . Please note that the metal layers 12 and 13 are usually made of copper and are usually patterned in accordance with the wiring layers 16 and 17 .

Then, in Step S 14 , the wiring layers 16 and 17 along with their respective metal layers 12 and 13 are separated from the base. As shown in FIG. 4A , which is a sectional diagram along the A-A′ line of FIG. 3B , by cutting along the borders where the wiring areas 12 a and rim areas 12 b of the wiring layers 16 and 17 interface with each other. The rim areas 12 b along with the side walls 10 a of the dielectric frame 10 are therefore removed, leaving two semi-products of the coreless substrate as shown in FIG. 4B .

Then, in Step S 16 , on the other sides of the metal layers 12 and 13 opposite to the wiring layers 16 and 17 , a number of wiring and/or resin layers 20 and 21 required by the coreless substrate are developed respectively. The result is two coreless substrates as shown in FIG. 4C . Please note that the metal layers 12 and 13 are not removed. Instead, they are part of the layers 20 and 21 . According to the foregoing description, the present invention indeed not only achieves the fabrication of coreless substrates, but also can double the production capacity as two coreless substrates are produced at once in a single process.

As a brief summary, the major characteristic of the present invention lies in the provision of a base and two metal layers on the top and bottom sides that are detachable from the base. Then, from the two metal layers respectively, the bump-pad side or ball-side wiring layers of a coreless substrate are developed simultaneously. Then, the two metal layers along with their respective bump-pad side or ball-side wiring layers are separated from the base into two semi-products of the coreless substrate. Then, from the other side of the metal layers (i.e., opposite to the bump-pad side or ball-side wiring layers), the other wiring layers required by the coreless substrate are developed to complete the fabrication process. As such, two coreless substrates are manufactured at once in a single process.

Based on the same principle, FIGS. 5A˜5D show another embodiment of the present invention. As shown in FIG. 5A , the base provided in Step S 10 is an organic disengagement layer 52 a and two copper foils 50 a and 50 b are adhered to its both sides. Due to the characteristic of the organic disengagement layer 52 a , the copper foils 50 a and 50 b can later be separated in Step S 14 . The organic disengagement layer 52 a can be implemented using various methods and quite a few techniques have already been disclosed in prior art. The details are therefore omitted here.

Then, in Step S 12 , wiring layers 46 and 47 are formed from the copper foils 50 a and 50 b respectively and simultaneously, as shown in FIG. 5B . Again, in Step S 14 , the copper foils 50 a and 50 b and their respective wiring layers 46 and 47 are separated from the organic disengagement layer 52 a , as shown in FIG. 5C . Finally, in Step S 16 , from the other sides of the copper foils 50 a and 50 b , wiring layers 56 a and 56 b are developed respectively, as shown in FIG. 5D . Please note that, in FIG. 5D , the copper foils 50 a and 50 b are not removed but are part of the wiring layers 56 a and 56 b.

Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.