High-density interconnect printed circuit board manufacturing method

Abstract

This invention relates to a method for manufacturing high-density interconnect printed circuit boards, comprising the following steps: Step 1: Cutting and fabricating an inner core board by mechanically drilling four mechanical through holes at the four corners, serving as first positioning through holes; Step 2: Using the pre-set first positioning through holes as positioning references, the first upper copper foil and the first lower copper foil are subjected to a first laser drilling process after browning; Step 3: Using the pre-set first positioning through holes as positioning references, an X-ray drilling target is fabricated, and simultaneously, first inner layer targets located at the four corners are fabricated; Step 4: Four mechanical through holes are set using an X-ray drilling machine, serving as second positioning through holes; Step 5: Precision positioning is performed using the first inner layer targets, followed by a second laser drilling process, and a ring target is fabricated; Step 6: Graphic positioning is performed using the first ring target, and graphic fabrication is carried out. The target and HDI board manufacturing method provided by this invention solves the problem of poor target recognition caused by electroplating filling, achieving a roundness of over 95%, thereby optimizing the individual differences between target holes, improving alignment accuracy, and making the interlayer offset of multilayer high-order blind holes less than 15μm, improving the overall interlayer alignment by about 30%.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit boards, and in particular relates to a method for manufacturing a high-density interconnect printed circuit board. Background Technology

[0002] Any-layer HDI (High-Density Interconnect) boards typically begin with the core board, where blind vias and patterns are fabricated. Layers are then laminated onto the outer layers, with patterns and signals connected vias. As the wiring and blind via density of any-layer HDI boards increases, the designed blind via diameters become smaller, and the pad sizes decrease. Furthermore, the core board thickness and the thickness of the add-on dielectric are also decreasing. As the material thins, the board rigidity weakens, leading to increased board deformation and placing higher demands on alignment accuracy.

[0003] Currently, the industry standard for transmitting alignment information between laser-drilled blind vias and patterned circuits in arbitrary-layer HDI boards can be broadly categorized into two types based on the alignment targets used: The first method uses mechanical through-holes drilled by X-ray after lamination for alignment of both the laser-drilled blind vias and the patterned circuits; the second method uses mechanical through-holes drilled by X-ray after lamination for coarse positioning of the laser-drilled blind vias, then uses a laser drill to burn out a pre-set inner layer target, and then precisely positions and manufactures a target for alignment between the laser-drilled hole and the pattern based on the inner layer target, and performs pattern alignment based on the manufactured pattern target.

[0004] The first method is unsuitable for manufacturing high-end HDI boards due to the discontinuous transmission of laser drilling and the alignment system of the patterned circuits, resulting in severe layer misalignment. The second method, for thinner HDI products, as described in the existing patent document "A High-End HDI Board Alignment Method" (Publication No.: CN 105392305 B), involves using laser drilling to burn out a pre-set inner layer target. Four pattern alignment target laser rings, precisely positioned according to the inner layer target, are distributed at the four corners of the board edge. Each laser ring consists of 12 0.2mm blind holes. For thinner HDI products, the interlayer dielectric thickness is relatively thin, causing it to be filled or partially filled during the fill-in electroplating process, making it difficult or impossible to identify the circuits during automatic LDI exposure. Simultaneously, the roundness of the laser rings decreases, resulting in a low target score during exposure, leading to deviation of the patterned blind holes, poor interlayer alignment, and a low product yield. Summary of the Invention

[0005] One of the objectives of this invention is to overcome the shortcomings of the prior art and provide a method for manufacturing high-density interconnect printed circuit boards.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A method for manufacturing high-density interconnect printed circuit boards, characterized by comprising the following steps:

[0008] Step 1: Cut the material to make the inner core board. The inner core board includes the core layer, the first upper copper foil and the first lower copper foil. Four mechanical through holes are set at the four corners by mechanical drilling as the first positioning through holes.

[0009] Step 2: Using the pre-set first positioning through hole as the positioning reference, the first upper copper foil and the first lower copper foil are laser-drilled for the first time after browning;

[0010] Step 3: After the first electroplating filling and copper reduction, the inner core board pattern circuit layer is made on the first upper copper foil and the first lower copper foil respectively. A substrate disk area is etched away on both the first upper copper foil and the first lower copper foil. Using the pre-set first positioning through hole as the positioning reference, an X-ray drilling target is made and the first inner target located at the four corners is made at the same time. The pattern of the first inner target includes a rectangular copper-free area and a positioning disk concentrically set with the copper-free area. The diameter of the positioning disk is 1.0mm.

[0011] Step 4: The PP layer copper foil layer includes a second core layer, a second upper copper foil layer, and a second lower copper foil layer; the PP layer copper foil layer is sequentially set on the inner core board pattern circuit layer, and the first lamination is performed; then, four mechanical through holes are set using an X-ray drilling machine as the second positioning through holes;

[0012] Step 5: After browning, the second upper copper foil and the second lower copper foil are subjected to a second laser drilling process. The second positioning through hole is used for rough positioning, and the second upper copper foil and the second lower copper foil are burned to expose the first inner target. The first inner target is used for fine positioning, and then the second laser drilling process is performed to create a ring target. The ring target is groove-shaped.

[0013] The ring-shaped target penetrates at least two layers of copper foil and extends to a third layer of copper foil;

[0014] Step 6: Locate the graphic using the first circular target and create the graphic.

[0015] Step 7: Repeat steps 4 to 6 to complete the addition of layers to the multilayer HDI board.

[0016] According to one technical solution of the present invention, the annular target is made of blind holes with a diameter of 0.1 mm and consists of three rings of laser holes. The spacing between the innermost and outermost laser holes is designed to be 1 / 3 of the diameter of the laser holes in the current layer unit. The middle ring of laser holes is located on the center line of the annular target and the spacing between the holes is designed to be 1 / 2 the diameter of the laser holes in the current layer unit.

[0017] The present invention has the following beneficial effects:

[0018] This invention effectively solves the problem of target flattening or partial flattening during through-hole plating, leading to difficulty or inability to identify the target during automatic LDI exposure, by using an inner layer design with an annular groove target spanning two circuit layers. This improves the interlayer alignment of high-density interconnect printed circuit boards. Simultaneously, it addresses the issue of reduced roundness of the laser ring, resulting in low exposure target scores and thus deviation of blind vias and poor interlayer alignment. The second positioning hole is changed to an annular groove, improving roundness by over 95%, further enhancing exposure alignment and interlayer alignment. The interlayer offset of multi-layer high-order blind vias is less than 15μm, and the overall interlayer alignment is improved to approximately 30%. Attached Figure Description

[0019] Figure 1 This is a partial cross-sectional view of the product structure after steps 1-3 of the present invention are completed.

[0020] Figure 2 This is a partial cross-sectional view of the product structure after step 4 of the present invention.

[0021] Figure 3 This is a partial cross-sectional view of the product structure after step 5 of the present invention.

[0022] Figure 4 This is a schematic diagram of the product structure after step 5 of the present invention.

[0023] Figure 5 This is a schematic diagram showing the measurement of the center distance between two layers of graphics.

[0024] Figure 6 This is a schematic diagram of the distance between the laser blind hole and the center of the chassis (Y direction).

[0025] Figure 7 This is a schematic diagram (Y direction) showing the distance between the laser blind hole and the center of the top plate.

[0026] Figure 8 This is a diagram showing the alignment effect of interconnected vias in a stack of 10 arbitrary layers. Detailed Implementation

[0027] A method for manufacturing high-density interconnect printed circuit boards, comprising the following steps:

[0028] like Figure 1 As shown, step 1: cut and manufacture inner core board 10. Inner core board 10 includes first core layer 11, first upper copper foil 12 and first lower copper foil 13. Four mechanical through holes are set at the four corners by mechanical drilling as first positioning through holes 14.

[0029] Step 2: Using the pre-set first positioning through hole 14 as the positioning reference, the first upper copper foil 12 and the first lower copper foil 13 are laser-drilled for the first time after browning.

[0030] Step 3: After the first electroplating filling and copper reduction, inner core board pattern circuit layers are fabricated on the first upper copper foil 12 and the first lower copper foil 13 respectively. A substrate disk area 15 with a diameter of 3mm is etched off on both the first upper copper foil 12 and the first lower copper foil 13. Using the pre-set first positioning through hole 14 as the positioning reference, an X-ray drilling target is fabricated and the first inner target 16 located at the four corners is fabricated at the same time. The pattern of the first inner target 16 includes a rectangular copper-free area 17 and a positioning disk 18 concentrically set with the copper-free area. The positioning disk 18 has a diameter of 1.0mm.

[0031] like Figure 2 As shown, step 4: the PP layer copper foil layer 20 includes a second core layer 21, a second upper copper foil 22 and a second lower copper foil 23; the PP layer copper foil layer 20 is sequentially set on the pattern circuit layer of the inner core board 10, and then the first pressing is performed. Then, four mechanical through holes are set by an X-ray drilling machine as the second positioning through holes 24.

[0032] like Figure 3 , 4 As shown, in step 5: after browning, the second upper copper foil 22 and the second lower copper foil 23 undergo a second laser drilling process. Coarse positioning is performed using the pre-set second positioning through-hole 24, and the second upper copper foil 22 and the second lower copper foil 23 are burned to expose the pre-set first inner target 16. Fine positioning is performed using the first inner target 16, followed by a second laser drilling process to create an annular target 25. The annular target 25 is groove-shaped, with an outer ring diameter of 2.3 mm and an inner ring diameter of 1.7 mm.

[0033] The annular target penetrates at least two layers of copper foil and extends to a third layer of copper foil; that is: the annular target 25 made from one side of the second upper copper foil 22 penetrates the second upper copper foil 22 and the first upper copper foil 12, and extends to the first lower copper foil 13; that is: the annular target 25 made from one side of the second lower copper foil 23 penetrates the second lower copper foil 23 and the first lower copper foil 13, and extends to the first upper copper foil 12;

[0034] The ring target is made of blind holes with a diameter of 0.1 mm and consists of three rings of laser holes. The spacing between the innermost and outermost laser holes is designed to be 1 / 3 of the diameter of the laser holes in the current layer unit. The middle ring of laser holes is located on the center line of the ring target, and the spacing between the holes is designed to be 1 / 2 the diameter of the laser holes in the current layer unit.

[0035] Figure 1-3 The schematic diagram of the first positioning hole 14, the second positioning hole 24, and the annular groove 25 at only one corner of the circuit board is shown.

[0036] Step 6: Locate the graphic using the first circular target and create the graphic.

[0037] We collected target hole alignment scores for an L3 / 4 layer LDI exposure machine on a 10-layer arbitrary layer interconnect HDI board under two different targets. The higher the score, the higher the probability of the alignment point being accepted and the higher the alignment accuracy. As shown in the following results, the target hole alignment score of the method of this invention is improved from 86.2% to 95.6% compared with the target in patent document CN105392305B, and the average standard deviation is improved from 0.04 to 0.012. This optimizes the individual differences between target holes and thus improves the alignment accuracy.

[0038] Table 1: Comparison of target hole alignment scores between the two methods

[0039]

[0040] When measuring alignment, the center distance between two adjacent layers of graphics is collected to evaluate the alignment accuracy between layers. Figure 5 This is a schematic diagram of the measurement of the center distance between two layers of patterns; the distance between the center of the laser blind hole and the center of the laser hole disk between two adjacent layers is collected to evaluate the alignment accuracy of the laser blind hole and the pattern, including the alignment accuracy of the laser hole and the base and the alignment accuracy of the laser hole and the hole disk. Figure 6 This is a schematic diagram (Y direction) showing the distance between the laser blind hole and the chassis center. Figure 7 A schematic diagram of the distance between the laser blind hole and the center of the top plate (Y direction) for measuring the distance from the ground. Figure 8 This is a diagram showing the alignment effect of interconnected vias in a stack of 10 arbitrary layers.

[0041] The alignment accuracy between adjacent layers (L3 / 4) and the alignment accuracy between laser apertures and patterns of a 10-layer arbitrary-layer interconnect HDI board were collected under two different targets; where X represents the center distance in the X direction, Y represents the center distance in the Y direction, and D represents the center distance between the two disks; the results are as follows:

[0042] Table 2: Alignment of graphics between adjacent layers

[0043]

[0044] Table 3: Alignment between laser blind hole and chassis

[0045]

[0046] Table 4: Alignment between laser blind hole and top plate

[0047]

[0048]

[0049] Based on the data in the table above, whether it is the alignment between layers of patterns or the alignment between laser holes and inner and outer layer patterns, the alignment accuracy of multi-layer laser slot targets is improved from less than 20um to less than 13um compared with single-layer laser hole targets, which is about 30% higher. This can better meet the requirements of high-precision HDI board layer alignment.

[0050] Table 5: Accuracy Comparison of Two Targets

[0051]

[0052] This invention effectively solves the problem of target flattening or partial flattening during through-hole plating, leading to difficulty or inability to identify the target during automatic LDI exposure, by using an inner layer design with an annular groove target spanning two circuit layers. This improves the interlayer alignment of high-density interconnect printed circuit boards. Simultaneously, it addresses the issue of reduced roundness of the laser ring, causing blind via misalignment and poor interlayer alignment. The second positioning hole is changed to an annular groove, improving roundness by over 95%, further enhancing exposure alignment and interlayer alignment. The interlayer offset of multi-layer high-order blind vias is less than 15μm, and the overall interlayer alignment is improved to approximately 30%.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions or improvements within the spirit of the present invention are covered within the scope of the claims of the present invention.

Claims

1. A method for manufacturing a high-density interconnect printed circuit board, characterized in that, Including the following steps: Step 1: Cut the material to make the inner core board. The inner core board includes the core layer, the first upper copper foil and the first lower copper foil. Four mechanical through holes are set at the four corners by mechanical drilling as the first positioning through holes. Step 2: Using the pre-set first positioning through hole as the positioning reference, the first upper copper foil and the first lower copper foil are laser-drilled for the first time after browning; Step 3: After the first electroplating filling and copper reduction, the inner core board pattern circuit layer is made on the first upper copper foil and the first lower copper foil respectively. A substrate disk area is etched away on both the first upper copper foil and the first lower copper foil. Using the pre-set first positioning through hole as the positioning reference, an X-ray drilling target is made and the first inner target located at the four corners is made at the same time. The pattern of the first inner target includes a rectangular copper-free area and a positioning disk concentrically set with the copper-free area. Step 4: The PP layer copper foil layer includes a second core layer, a second upper copper foil layer, and a second lower copper foil layer; the PP layer copper foil layer is sequentially set on the inner core board pattern circuit layer, and the first lamination is performed; then, four mechanical through holes are set using an X-ray drilling machine as the second positioning through holes; Step 5: After browning, the second upper copper foil and the second lower copper foil are subjected to a second laser drilling process. The second positioning through hole is used for rough positioning, and the second upper copper foil and the second lower copper foil are burned to expose the first inner target. The first inner target is used for fine positioning, and then the second laser drilling process is performed to create a ring target. The ring target is groove-shaped. The ring-shaped target penetrates at least two layers of copper foil and extends to a third layer of copper foil; Step 6: After electroplating, the graphic is positioned using the first annular target to create the graphic; Step 7: Repeat steps 4 to 6 to complete the addition of layers to the multilayer HDI board.

2. The method for manufacturing a high-density interconnect printed circuit board according to claim 1, characterized in that, The ring target is made by stacking blind holes, consisting of three rings of laser holes. The spacing between the innermost and outermost laser holes is designed to be 1 / 3 of the diameter of the laser holes in the current layer unit. The middle ring of laser holes is located on the center line of the ring target, and the spacing between the holes is designed to be 1 / 2 the diameter of the laser holes in the current layer unit.

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