one. Foreword:
Benqiang Circuit has been committed to the research and development and manufacturing of high-end PCB express samples. The company is highly focused on the research and development of high-end, high-end HDI boards, high-frequency, high-speed, and high-difficulty PCB circuit boards with special processes; currently, the company's monthly sample shipments are 10,000 + models and are constantly making breakthroughs and innovations, and the delivery categories are constantly innovating.
The company has continuously increased its investment in independent research and development in recent years. After the completion of the delivery of 7-level HDI in 2020, it successfully opened up the 4-7 level high-end arbitrary interconnection HDI market, and based on this, launched high-rise thick diameter (25:1) in early 2021. A 36-layer 2-level semiconductor test board, a 10-layer HDI groove board with arbitrary interconnection was developed in August this year, and a buried resistance board of high transmission rate material was successfully developed in early September; our company successfully developed a This 12-layer depth-controlled 5-level arbitrary interconnect board has successfully opened up this type of manufacturing process to fill a gap in the industry.
Our company's HDI production level has reached the top of the industry and has been highly recognized by the industry. With the continuous expansion of the HDI market, PCB boards have certain requirements for aperture and insulation thickness based on different overcurrents, impedances, etc. during design. Due to Laser drilling is affected by the thickness of the hole diameter and cannot meet any interconnection requirements. It is necessary to use depth-controlled holes to complete electrical performance connections and achieve impedance.

2. Overview of any interconnection control depth hole plate:
The current implementation of arbitrary interconnection technology on HDI circuit boards is mainly through laser drilling and then sinking copper plates for electrical conduction and then laser superposition to complete the production of arbitrary interconnection lines. Laser drilling uses laser energy to control the depth and diameter of the drilling, and has Limitations (maximum laser aperture 0.2mm, maximum media thickness 0.15mm);
Since some products have requirements for impedance and current (overcurrent), there is a need to thicken and enlarge the media thickness and aperture when designing the PCB board. However, the conventional HDI laser drilling process cannot realize this process, so a method is invented to control the Processing of arbitrary interconnection of circuit boards by deep drilling multiple holes;

3. Product structural characteristics
Specific parameters of this 5th level HDI board product

Four. Introduction to key process technologies:
1. 12-layer 5-level HDI requires 5 laminations. Each lamination requires depth-controlled drilling, electroplating holes, resin plugged holes, circuit patterns, etching, etc. The electrical connection of each layer is achieved through buried blind hole lamination. The production process is lengthy, with a total of 92 processes and numerous control points. Including technical difficulties such as the alignment of multi-stage controlled deep hole stacked holes, the fullness of resin plug holes, and the production of fine circuits in each layer, the production is very difficult.

2.Laminated structure analysis:
Conventional depth-controlled blind hole products in the industry are 1-2 stages. The more stages, the greater the probability of layer deviation and depth control deviation.
This product is a 12-layer 5-step board with a blind hole structure of 5+N+5. The specific blind hole structures are 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 2-3, 3 -4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 2-11, 3-10, 4-9, 5-8 , 6-7, 2-12, a total of 25 sets of blind holes. see picture 1)

Figure (1) 5-level depth controlled HDI board structure diagram

3.Connection method
Through the 0607 layer core board, 5 times of lamination, 5 times of depth-controlled drilling, the holes are connected through depth-controlled holes and then resin plugged holes to achieve interconnection. Among them, the 0607 layer drills through-hole resin plugged holes, and the other holes have a diameter of 0.3mm. The step thickness is 0.24mm to achieve the connection hole through depth control drilling. See picture (2)

Figure (2) 5th level controlled depth slice diagram

4. Line coefficient prevention
After 5 laminations, pre-release is the key. The expansion and contraction caused by each lamination must be considered to give the pre-release coefficient of the initial core board (layer 0607). This coefficient will directly affect the production of subsequent boards, especially Control the accuracy of depth stacked holes.

5. Controlled depth drilling
Five depth-controlled drillings are the main difficulty control point. There are accuracy problems with mechanical drilling, and the holes are offset and shallow. The performance of the drilling rig directly affects the depth of the hole. Before operation, it is necessary to test the flatness of the drilling machine and select the thickness of the backing plate; Depth Control Drilling Diagram (3)

Depth control drilling diagram (3)

6. Electroplating plated holes
The depth-thickness-diameter ratio needs to be ≦1:1 to ensure the effect of copper immersion and copper plating; see Figure (4)

Figure (4) Controlled depth electroplated holes

7. Resin plug hole
It is difficult to control resin plugging holes 6 times. Controlling deep hole plugging will cause bubbles in the hole and poor hole plugging. Electroplating hole parameters are the key. It is necessary to ensure the hole copper and control the hole surface copper. Sufficient size of the hole must be reserved. , requires good penetration plating ability. See Figure (5)

Figure (5) Resin plug hole
8.Graphic plating
The line width and line spacing are 0.08/0.09. The graphics in the board are isolated, and the electro-etching of the graphics is prone to film clipping and thin lines.

5. Sharing picture of the finished product; see picture (6)

Figure (6) 5th level HDI depth control finished product display