As HDI board adapts to the development of high integration IC and high density interconnection assembly technology, it pushes PCB manufacturing technology to a new level and becomes one of the biggest hot spots in PCB manufacturing technology!In all kinds of PCB cam production, the personnel engaged in cam production agree that HDI mobile phone board has complex shape and high wiring density, so it is difficult to make cam quickly and accurately!Facing the requirements of high quality and fast delivery, I have some experience through continuous practice and summary. I would like to share with you cam peers.
1、 How to define SMD is the first difficulty in cam production
In the process of PCB production, graphic transfer, etching and other factors will affect the final graphics. Therefore, we need to compensate the line and SMD respectively according to the customer’s acceptance standard in cam production. If we don’t define SMD correctly, some SMD of finished products may be smaller.Customers often design 0.5mm CSP in HDI mobile phone board, the pad size is 0.3mm, and there are blind holes in some CSP pads, and the pad corresponding to the blind hole is just 0.3mm, so that the CSP pad and the pad corresponding to the blind hole overlap or cross together.In this case, it is necessary to operate carefully to prevent mistakes.(take genesis2000 as an example)
Specific production steps:
1. Close the drilling layer corresponding to blind hole and buried hole.
2. Define SMD
3. With the function of featuresfilterpopup and reference selection pop-up, find the pad of include blind hole from top layer and bottom layer, and move tot layer and B layer respectively.
4. In t layer (CSP pad layer), select and delete the 0.3mm pad which is in touch with the blind hole, and delete the 0.3mm pad in the CSP area of the top layer.Then, according to the size, position and number of CSP pads designed by customers, make a CSP and define it as SMD. Then copy the CSP pad to the top layer and add the pad corresponding to the blind hole in the top layer.Layer B is made in a similar way.
5. Find out other SMDS with missing or multiple definitions according to the network files provided by customers.
Compared with the conventional production method, the purpose is clear and the steps are less. This method can avoid misoperation and is fast and accurate!
2、 Removing non functional pads is also a special step in HDI handset board
First, remove the non functional layer 7 in pad 2, and then take the non functional hole 2 as the corresponding one.
The steps are as follows:
1. Nfpremovel function is used to remove the corresponding pad of nonmetallic holes in top and bottom layers.
2. Close all drilling layers except through-hole, select no for remove underriledpads in nfpremovel function, and remove 2-7 layers of non-functional pads.
3. Close all drilling layers except 2-7 layers of buried holes, and select no for remove unrilled pads in nfpremovel function, and remove 3-6 layers of non-functional pads.
Using this method to remove the non functional pad, clear thinking, easy to understand, the most suitable for just engaged in cam production personnel.
3、 On laser drilling
The blind hole of HDI mobile phone board is generally about 0.1 mm micropore. Our company adopts CO2 laser. Organic materials can strongly absorb infrared ray. Through thermal effect, the hole is ablated. However, the infrared absorption rate of copper is very small, and the melting point of copper is high. CO2 laser can not ablate copper foil, so the “conformal mask” process is used,Etch the copper skin of laser drilling hole with etching solution (CAM needs to make exposure film).At the same time, in order to ensure that there is copper skin in the sub outer layer (the bottom of the laser hole), the distance between the blind hole and the buried hole should be at least 4 mil. Therefore, we must use analysis / fabric / board drill checks to find out the holes that do not meet the conditions.
4、 Plug hole and solder mask
In the lamination configuration of HDI, RCC material is generally used for the secondary and outer layers, and its dielectric thickness is thin and the glue content is small. According to the technological experimental data, if there is one of the finished plate thickness greater than 0.8mm, metallized groove greater than or equal to 0.8mmX2.0mm, and metallized hole greater than or equal to 1.2mm, two sets of hole plugging documents must be made. That is, plug the hole twice, the inner layer is leveled with resin, and the outer layer is directly plugged with solder resist ink before solder resist. In the process of solder resist fabrication, there are often vias on or next to SMD. Customers require all vias to be plugged, so it is easy for the vias exposed or half of the holes exposed during solder resist exposure to take oil. CAM staff must deal with this. In general, we first remove the via hole. If the via hole cannot be removed, follow the following steps:
1. Add a light transmission point 3MIL smaller than the single side of the finished product hole on the solder resist layer at the via hole position that is Covered by solder resist.
2. Add a light transmission point 3MIL larger than the single side of the finished hole on the solder resist layer at the via hole position of the solder resist window Touch. (In this case, the customer allows a little ink on the pad)
V. Shape making
HDI mobile phone boards are usually delivered by splicing, with complex appearance, and customers are required to attach a copy of CAD drawings. If we use genesis2000 to draw according to the customer’s drawings, it is quite troublesome. We can change the CAD format file *.dwg to “AutoCADR14/LT98/LT97DXF(*.DXF)” by directly clicking “Save As” in the file, and then read the *.DXF file in the normal way of reading genber files. At the same time of reading the shape, the sizes and positions of stamp holes, positioning holes and optical positioning points are quickly and accurately read.
Sixth, milling the outline frame.
When milling the outline frame, unless the customer requires to expose the copper in the CAM production, in order to prevent the copper skin from turning over at the edge of the board, according to the production specification, it is required to cut a little copper skin into the board in the frame, so it is inevitable that the situation as shown in Figure 2A will occur! If the two ends of A are not in the same network, and the width of the copper skin is less than 3mil (the figure may not be made), it will cause an open circuit. This kind of problem can’t be seen in the analysis report of genesis2000, so we must find another way. We can make one more network comparison, and in the second comparison, cut the copper skin close to the frame into the board by 3 mils. If the comparison result is not open, it indicates that both ends of A belong to the same network or the width is greater than 3 mils (you can make a graph). If there is an open circuit, widen the copper skin.
