First and Second Stage Production Processes of HDI PCB Circuit Boards

First and Second Stage Production Processes of HDI PCB Circuit Boards

1. After pressing the HDI circuit board once, drill the hole==>Press the copper foil again on the outside==>Laser again ->First order

2. After pressing the HDI circuit board once, drill holes==>press the copper foil again on the outside==>laser again, drill holes==>press the copper foil again on the outer layer==>laser again ->second stage.

It mainly depends on how many times you laser, which is the order.

Below is a brief introduction to the HDI circuit board process for PCB boards. Basic knowledge and production process: With the rapid changes in the electronics industry, electronic products are developing towards lightweight, thin, short, and compact sizes. Correspondingly, printed circuit boards are also facing challenges of high precision, thin lines, and high density. The trend in the global market for printed circuit boards is to introduce blind and buried holes in high-density interconnect products, in order to more effectively save space and make line width and spacing thinner and narrower.

1、 HDI Definition HDI: The abbreviation for High Density Interconnection (HDI) refers to a multi-layer HDI circuit board made by the incremental layer method, which features high-density interconnects, non mechanical drilling, micro blind hole rings with a width/gap of less than 6mil, inner and outer layer wiring with a width/gap of less than 4mil, and pad diameters not exceeding 0.35mm.

Blind hole: short for Blind hole, realizing the connection and conduction between the inner and outer layers. Buriedvia, short for Buriedvia, realizing the connection and conduction between the inner and inner layers. Blind access holes are mostly small holes with a diameter of 0.05mm~0.15mm. The drilling methods for blind holes include laser drilling, plasma etching, and photo induced drilling. Laser drilling is usually used, and laser drilling is divided into CO2 and YAG ultraviolet laser machines (UV).

2、 HDI circuit board material

1. HDI circuit board materials include RCC, LDPE, FR41) RCC: Resin coated copper foil. RCC is composed of copper foil and resin that have undergone surface roughening, heat resistance, oxidation resistance, and other treatments. Its structure is shown in the following figure: (used when thickness>4mil) The resin layer of RCC has the same processability as FR-4 adhesive sheet (Prepreg). In addition, it is necessary to meet the performance requirements of multi-layer HDI circuit boards using the stacking method.

(1) High glass transition temperature (Tg);

(2) Low dielectric constant and low water absorption rate;

(3) Has high adhesion and strength to copper foil;

(4) High insulation reliability and micro via reliability;

(5) After curing, the thickness of the insulation layer is uniform. As RCC is a new type of product without glass fibers, it is beneficial for laser and plasma etching treatment, as well as for the lightweighting and thinning of multi-layer boards.

In addition, resin coated copper foil has thin copper foils such as 12pm and 18pm, which are easy to process. 2) LDPE: 3) FR4 sheet: Used when thickness<=4mil. When using PP, it is generally recommended to use 1080 and avoid using 2116 PP2. Copper foil requirements: When the customer has no requirements, the copper foil on the substrate should preferably use 1OZ for the traditional PCB inner layer, HOZ for HDI boards, and 1/3OZ for the inner and outer electroplated copper foils.

3、 HDI circuit board laser hole formation: CO2 and YAGUV laser hole formation. The principle of laser hole formation is that laser light is a strong beam of light excited by external stimuli and increased energy. Infrared or visible light has thermal energy, while ultraviolet light has chemical energy. When it hits the surface of a work object, three phenomena occur: reflection, absorption, and transmission, among which only the absorbed object takes effect. And its effect on the board is divided into two different reactions: photothermal ablation and photochemical cracking.

1. YAG UV laser hole formation: It can concentrate small light beams, and the copper foil has a relatively high absorption rate. It can remove copper foil and burn micro blind holes below 4mil. Compared with CO2 laser hole formation, there is basically no resin residue at the bottom of the hole, but it is easy to damage the copper foil at the bottom of the hole. The energy of a single pulse is very low, and the processing efficiency is low. (YAG, UV: wavelength: 355, relatively short wavelength, can process very small holes, can be absorbed by resin and copper at the same time) No special window opening process is required. 2. CO2 laser hole making: using an infrared CO2 laser machine, CO2 cannot be absorbed by copper, but can absorb resin and glass fiber, generally 4-6 mil micro blind holes.

The hole forming method of HDI circuit board is as follows:

A. The ConformalMask method involves first pressing RCC on the inner core board, then opening a copper window, and then using laser light to burn off the substrate inside the window to complete micro blind holes. The details are to first make the inner core board of FR-4, with blackened lines and targets on both sides, and then press it together. Then, according to the etched copper window film, remove the copper skin corresponding to the blind hole position, and use CO2 laser light to burn off the resin inside the window, which can be hollowed out to form micro blind holes on the bottom pad. This method was originally a patent of Hitachi Ltd. (copper windows and blind holes of the same size), and general operators may need to be careful of legal issues when shipping to the Japanese market.

B. The Large Conformalmask method involves enlarging the copper window to a size approximately 1mil larger than one side of the blind hole. Generally, if the aperture is 6mil, the large window can be opened to 8mil. Our company adopts this method for operation.

4、 Laser drilling blind buried hole operation process explained with 1+2+1 as an example

Production process: Cutting - Opening large copper window - Drilling L2~L3 buried holes - Removing adhesive residue - Electroplating buried holes - Resin plug holes - Inner layer graphics - Pressing - L1-2&L4-3 layers of LargeWindows (copper window is 1mil larger than blind hole aperture on one side) (etching) - Laser drilling of blind holes on L1-2&L4-3 layers - Removing adhesive residue twice - Electroplating blind holes (pulse electroplating) - Resin plug holes - Grinding plate+copper reduction - Mechanical drilling through holes - Normal process 2+4+2 process cutting - L3~6 layer graphics - Pressing - Opening large copper windows - Laser buried holes on L23&L76 layers - L26 mechanical drilling - Removing adhesive Slag → Electroplating buried hole → Resin plug hole - L2, L7 layer graphics → Pressing → Opening large copper window → Laser for L12&L87 layers → Removing adhesive slag - Electroplating blind hole - Resin plug hole - Grinding plate+copper reduction - Mechanical drilling - Normal process