Briefly introduce the HDI circuit board process of the PCB board. Basic knowledge and production process With the rapid changes in the electronics industry, electronic products are developing towards lightness, thinness, shortness and miniaturization. The corresponding printed circuit boards also face the challenges of high precision, thinning and high density. The trend of printed boards in the global market is to introduce blind and buried vias in high-density interconnect products, so as to save space more effectively and make the line width and line spacing thinner and narrower.
1. HDI definition HDI: short for highDensityinterconnection, high-density interconnection, non-mechanical drilling, micro-blind hole ring below 6mil, wiring line width/line gap between inner and outer layers is below 4mil, and the diameter of the pad is not greater than 0.35mm The build-up method of multilayer HDI circuit boards is called HDI circuit boards.
Blind via: short for Blindvia, which realizes the connection between the inner layer and the outer layer. Blind hole: short for Buriedvia, which realizes the connection between the inner layer and the inner layer. Most of the blind holes are 0.05mm~0.15mm in diameter The hole forming method of buried blind hole includes laser hole forming, plasma etching hole and photoinduced hole forming, usually laser hole forming, and laser hole forming is divided into CO2 and YAG ultraviolet laser machine (UV).
2. HDI circuit board material
2.1. HDI circuit board materials include RCC, LDPE, FR41) RCC: short for Resincoated copper, resin-coated copper foil. RCC is composed of copper foil and resin whose surface has been roughened, heat-resistant, anti-oxidative, etc. Its structure is shown in the figure below: (used when the thickness is >4mil) The resin layer of RCC has a bonding sheet with FR-4 (Prepreg) the same manufacturability. In addition, it must meet the relevant performance requirements of the multi-layer HDI circuit board of the build-up method.
a. High glass transition temperature (Tg);
b, low dielectric constant and low water absorption;
c. High adhesion and strength to copper foil;
d. High insulation reliability and micro-via reliability;
e. The thickness of the insulating layer after curing is uniform and at the same time, because RCC is a new type of product without glass fiber, it is conducive to the etching process of laser and plasma, and is conducive to the lightweight and thinning of multi-layer boards.
2.2. The resin-coated copper foil has thin copper foils such as 12pm and 18pm, which are easy to process. LDPE: 3) FR4 sheet: used when the thickness is <= 4mil. When using PP, generally use 1080, try not to use 2116 PP2. Copper foil requirements: when the customer has no requirements, the copper foil on the substrate is preferred to use 1OZ in the inner layer of the traditional PCB, the HDI board is preferred to use HOZ, the inner and outer electroplating layer copper foil is preferred Use 1/3OZ.
3. Laser hole formation of HDI circuit board: CO2 and YAGUV laser hole formation The principle of laser hole formation: Laser light is a powerful beam excited when the "ray" is stimulated by external stimulation and the energy is increased, among which infrared light or Visible light has thermal energy, and ultraviolet light has chemical energy. When it hits the surface of the work object, three phenomena, such as reflection, absorption, and transmission, will occur, of which only the absorbed will have an effect. And its effect on the plate is divided into two different reactions: photothermal ablation and photochemical cracking.
YAG's UV laser hole forming: It can gather tiny light beams, and the copper foil has a relatively high absorption rate. It can remove the copper foil and can burn micro blind holes below 4 mil. Compared with CO2 laser hole forming, the resin will remain at the bottom of the hole. There is basically no resin remaining 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 small, and the processing efficiency is low. (YAG, UV: wavelength: 355, the wavelength is quite short, can process very small holes, can be absorbed by resin and copper at the same time) No special windowing process is required 2.CO2 laser hole forming: using infrared CO2 laser machine, CO2 cannot be absorbed by copper, but it can absorb resin and glass fiber, generally 4~6mil micro blind holes.
The hole forming method of the HDI circuit board is as follows:
a. The copper window method ConformalMask is to press the RCC on the inner core board first, then open the copper window, and then burn the substrate in the window with laser light to complete the micro blind hole. The details are to first make the inner core board of FR-4, so that both sides have blackened lines and targets (TargetPad), and then press them together, and then remove the corresponding copper skin according to the copper etching window film to remove the blind hole position and then use CO2 laser. By burning off the resin in the window, the bottom pad can be hollowed out to form a micro-blind hole. (The size of the copper window is the same as that of the blind hole.) This method was originally a patent of "Hitachi Manufacturing Co., Ltd.", and general manufacturers may need to be careful about legal issues when they want to ship to the Japanese market.
b. Large copper window method LargeConformalmask The so-called "large window method" is to expand the copper window to about 1 mil larger than the blind hole on one side. Generally, if the aperture is 6mil, the large window can be opened to 8mil. Our company works this way.
4. The operation process of laser drilling blind and buried holes is explained by taking 1+2+1 as an example
Production process: cutting material - opening large copper windows - drilling L2~L3 buried holes - removing glue residue - electroplating buried holes - resin plug holes - inner layer graphics - pressing - L1-2&L4-3 Layer LargeWindows (the copper window is 1 mil larger than the blind hole diameter on one side) (etching) —— L1-2 & L4-3 layers of laser drilling blind holes —— Removing glue slag twice —— Electroplating blind holes (pulse electroplating)—— Resin plug hole -- grinding plate + copper reduction -- mechanical drilling through hole -- normal process 2+4+2 process cutting material → L3~6 layer graphics → pressing → opening large copper window → L23&L76 layer Laser buried hole → L26 mechanical drilling → glue removal → electroplating buried hole → resin plug hole—–L2, L7 layer pattern → lamination → large copper window → L12&L87 layer Laser → glue removal → electroplating blind hole--resin plug hole- - Grinding plate + copper reduction - mechanical drilling - normal process.
1. After the HDI circuit board is pressed once, drill the hole == "Press the copper foil again on the outside ==" and then laser——-" first order
2. After the HDI circuit board is pressed once, drill == "press copper foil on the outside again ==" and then laser, drill = "press copper foil on the outer layer again ==" and then laser ---" second order.
The main thing is to see how many times your laser is, which is how many steps.
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