Build-up method for manufacturing high density inner connection (HDI) printed boards;
Semi-additive method to make precision thin wire (0.08mm/0.08mm line width spacing) technology;
Thermosetting ink layer method (referred to as TCD) technology;
Electroplating Blind Filling Technology (Via Filling);
High-grade special materials printed board manufacturing technology.
1. Fabrication of High-Density Inner-layer Connection (HDI) PCB Technology
Build-up method is a kind of new technology that cooperates with blind-hole plate manufacturing. The method is to first process the inner layer by the common multi-layer board processing method, and then superimpose one layer, two or more layers on top and bottom, we call Add layer or SBU layer. The SBU layer communicates with its neighboring layers through micro-vias (ie, blind holes). To truly master this technology, you must first master the following technologies:
A. Laser drilling technology
Although the use of laser drilling machine can drill 2mil-8mil blind holes, but the laser drilling technology is much more complicated than ordinary mechanical drilling, when the S anti-material is different, the plate thickness is different, the required laser energy is different when the aperture is different. Therefore, we must go through systematic tests and tests before we can find the drilling parameters that are suitable for all kinds of plates, so as to ensure the drilling quality.
B. Micro-via plating technology
The HDI board usually contains buried and blind holes, the buried hole diameter is about 0.3 mm, and the blind hole diameter is 0.1-0.15 mm. The minimum hole size in common PCB is 0.5mm, and there is no blind hole. Therefore, to produce HDI boards, blind hole plating is a problem that must be solved.
The use of positive and negative pulse plating power supply, combined with improved plating line design, can ensure that the thickness ratio of the plating layer on the blind hole to the surface plating layer is close to or higher than 1:1, ensuring that the HDI board has good reliability.
C. Fine line production technology
Another feature of high-density circuit boards is their small line width and line spacing. To make lines below 4mil, using a traditional stereographer, the stereolithography is difficult to achieve. Need to use advanced DES (developing, etching, stripping) line, and with suitable dry film and exposure technology can be achieved. The research focuses on the production of 3mil/3mil linewidth, and then study 2mil/3mil, 2mil/2mil.
2. Thermoset ink lamination technique (referred to as TCD technology)
TCD technology is a new technique for replacing the platen with a method of fabricating the SBU layer in the HDI board using silk screen thermosetting ink.
The advantages of TCD technology are:
A. The dielectric thickness of the SBU layer is adjustable. The user needs thicker dielectric layers and more heat-sealable inks with thicker screens than the fixed thickness of semi-solids.
B. Laser drilling is easy to achieve. Because the main component of the ink is resin and does not contain glass, the required laser energy is lower and more stable than the epoxy glass cloth in the prepreg. Therefore, the laser drilling is easy to control.
C. The manufacturing cost is greatly reduced. Because laser drilling glass cloth technology is difficult to control, some manufacturers first use a copper foil with semi-cured resin (RCC for short) that does not contain glass cloth. This type of RCC is only produced in Japan and is expensive, so using TCD technology can achieve the same effect without using RCC.
D. Simplify the production process. After printing the ink in the TCD process, the laser can be directly used for drilling. If other materials such as RCC are selected, the copper window must be opened at the position where the plate is to be drilled before the laser drilling can be performed.
The TCD process mainly includes the following technical content:
A. Plug Technology
Before screen-printing plastisol ink, plug the hole in the inner layer with stopper oil. If you do not plug the hole first, you will see a depression in the hole after the ink is printed. There is a bubble in the hole. The unevenness of the surface will directly affect the production of the circuit. The gas in the hole will expand under the condition of heating. Now the PCB can not pass the thermal shock test. Therefore, the quality of the plug hole is very important. Therefore, it must be ensured that 100% of the holes in the board are full.
B. Screen Printing Technology
For TCD technology, screen printing quality is one of the keys. How to control the thickness of the printed ink to meet the customer's required thickness after fully curing, how to ensure the ink's flatness, how to control the board's ink, how to control the board's warpage, etc. The problem that must be solved.
C. Ink surface roughening technology
The surface of the ink layer is well-coarsened to ensure good adhesion between the oil layer and the copper layer after PTH. When a wire is made in the copper layer, the wire tension should be ≥1.0kg/cm.
D. Electroless copper sink technology
The electroless copper plating on the entire surface of the ink layer is very different from the hole metallization of the common board. The hole metallization (PTH) process of a common plate deposits a layer of copper on the insulating layer in the hole so that the layers passing through the hole conduct. The non-electrolytic copper plating on the surface of the ink requires that the blind hole and the surface be uniformly deposited in the via hole. After being thickened by electroplating, the wire pull force of the oil layer should meet the standard requirements and the thermal shock (260°C) must be applied. After 20s) no stratification. This requires that the initial reaction rate without electrolyzing copper is slow and the internal stress is small, otherwise it will be stratified after thermal shock.
3. Semi-additive method for making fine thread technology
The main process flow of the semi-additive process is: Electroless copper plating on the entire board (generally copper layer thickness < 0.1mil, dry film, exposure, development process, and then the line and hole position map plating, electroplating faded The dry film is removed to form a circuit, and the advantage of this process is that only the bottom copper of the pattern plating (usually < 0.1 mil) is etched during etching, so that the stereolithography process does not bring about obvious side etching to the lines. The lines are distorted, so using the semi-additive method allows us to produce finer, smaller-pitch lines.To master this technique, we must first master the following key technologies:
A. Electroless thick copper technology
The electroless thick copper is different from the common electroless copper. It requires the thickness of the copper to be thicker than 0.05 mil. If the copper layer is too thin, it will be difficult to carry out the surface pretreatment by dipping the dry film. Because the plate is polished, the copper layer will be worn out to expose the substrate. Without the plate, the adhesion between the dry film and the copper may be affected. Therefore, it is necessary to use a suitable copper impregnated liquid, with specific process conditions, in order to obtain a satisfactory copper layer.
B. Graphic plating technology
Graphic plating technology is the most critical technology in semi-additive technology. Because each type of board has its own line layout, there are inevitably independent lines, large areas, thick lines, thin lines, etc. when wiring. For pattern plating, the unevenness of the wiring inevitably causes uneven current distribution. The charge on the independent lines is the most concentrated, so the plating thickness of the independent line and the thick line at the same position on the same plate will be significantly different. The uneven thickness of this coating will affect the uniformity of the green oil after screen printing and soldering.
The commonly used additive method is to form a circuit after the entire plate copper plating, and the plating uniformity of the whole plate plating will be much higher than the pattern plating. Therefore, to use the additive method to make thin lines, the layout of the plating plating must be resolved first. The use of forward and reverse pulse plating power supply, after adjusting the positive and negative pulse time, positive and negative pulse current and other parameters, so that the pattern plating can get a more uniform coating distribution.
4. Electroplating filling blind hole technology
The conventional HDI laser blind hole process faces the following problems: There is a hole in the blind hole of the SBU layer, and air may remain in the blind hole, which affects the reliability after thermal shock. The conventional method to solve this problem is to fill the blind hole cavity with resin or fill the blind hole with the resin ink plug hole process through the press plate. However, the reliability of the boards produced by these two methods is difficult and the production efficiency is low. In order to improve process capability and improve HDI process, the process of electroplating and filling blind holes has the advantage of filling blind holes with electroplated copper, which greatly improves reliability. At the same time, since the plate surface after electroplating has no depression, it can be on Making circuit patterns or superimposing blind holes greatly improves the process capability to adapt to customers' increasingly complex and flexible designs.