1. Brief introduction, blind holes and embedded fillers are mainly made of high-density and small microplates. Purpose depends on saving circuit space, so as to reduce PCB volume, such as mobile phone board.
Second, classification:
1). Laser drilling,
1. the reason for drilling with laser: a. customer data requires drilling with laser; B because the diameter of the blind hole is not large < =5MIL, it is necessary to drill the hole with laser. C, if there are blind holes in L1 to L2 and buried holes in L2 to L3, it is necessary to drill the hole with laser.
2. Principle of laser drilling: Laser drilling is to gasify or dissolve the plate into holes by absorbing laser heat, so the plate must have light absorption. Therefore, general RCC materials are not easy to reflect light because there is no glass fiber cloth in RCC.
3.RCC material introduction: RCC material is resin-coated copper foil: it consists of coating a layer of resin with distinctive characteristics on the rough surface of electrolytic copper foil. Three common suppliers: Shengyi Company, Mitsui Company, LG Company Material: resin thickness 5065707580(um) and other RCC materials with copper foil thickness S6018(um) and other RCC materials have high TG and low TG materials, and their dielectric constants are smaller than normal FR4, such as Guangdong.
4. Requirements for making special tools for laser drilling: a). It is difficult for laser to burn through the copper skin, so before laser drilling, a CuClearance.B with the same diameter as that of the blind hole should be etched. b). The precise positioning mark of laser drilling should be added on L2/LN-1 layer and marked on the change page of MI screen printing. C) The blind hole etching dot screen printing plate must be made of LDI, and the LDI plate specification must be used for cutting.
5. Features of production process: a). When the total number of lines is N, L2-LN-1 layers are finished according to the normal board steps, and b). After pressing the board and gong the field, the steps are changed to:-> drilling LDI precise positioning hole-> wet film-> etching blind hole point-> laser drilling-> drilling buried hole.
6. Other common problems: a). Because RCC materials are not certified by UL, this kind of board is not marked by UL for the time being. b). With regard to the layout structure on MI, in order to prevent this kind of RCC-containing board from being used as a fake multilayer board (because the screen printing room makes the screen printing fake multilayer board different from the normal board), we should pay attention to the separation of RCC materials from L2 or Ln-1 layers when drawing the layout structure. For example, SR2711/01 row board: C).IPC-6016 is HDI board specification: copper thickness of laser blind hole: 0.2mil(min). solder wire circle requirement: allowable tangent of circle. If PAD specification is less than 5mil larger than diameter, it is proposed to add TEARDROPD). Plate edge > =0.8 ”
Ii) Blind/Buried hole drilling by mechanical equipment:
1. Application field: Drilling with mechanical equipment can be considered when the specification of drill nozzle > = 0.20mm;
2. The electroplating method of blind buried hole (refer to RD notice TSFMRD-113):A). Under normal conditions, the copper surface of all layers of circuit can only be plated once by plate and plated once by pattern; B) Under normal conditions, after the whole pin step, the board thickness is > =80MIL, and the buried hole needs board plating+pattern plating, therefore, the external board surface cannot be plated during blind hole plating. C) After considering the two standards, the blind hole plating is carried out as follows: I). When the total width of the external line exceeds 5MIL and the thickness of the buried hole plate is less than 80MIL, the external board surface can cover the whole PCB during blind hole plating. III) When the boundary of the outer circuit graph is lower than 5MIL and the thickness of the buried hole plate is > =80MIL, the glass film is required to maintain the surface of the middle and outer layer of blind hole plating;
3. Method of glass film: 1) When the aspect ratio of blind hole is less than 0.8 (L/D), the whole PCB on the outer surface will be exposed with wet film, and the whole PCB on the inner surface will be electroplated; 2) When the aspect ratio of blind hole is more than 0.8 (L/D), the blind hole on the outer surface will be exposed with wet film, so it is necessary to make an electroplating exposure silk screen or LDI exposure, and the whole PCB on the inner surface of blind hole.
4. The way of blind hole exposure: 1) when the blind hole is < =0.4MM(16MIL), the blind hole is exposed by LDI; 2) when the blind hole is > 0.4MM(16MIL), the blind hole is exposed by silk screen.
5. Method of embedding glass film: 1) When the graphic boundary of the embedded hole surface is less than =4MIL, the embedded hole surface needs to be exposed with glass film; 2) When the graphic boundary of the embedded hole surface is greater than 4MIL, the embedded hole surface will be plated immediately.
6. Frequently asked questions: 1) In aspect ratio, L/D:L= material thickness+copper thickness, and D= blind hole/buried hole diameter. 2) Blind hole/buried hole electroplated screen: * diameter of exposure point D=D-6(MIL).* The exposed point screen is added with a pair of domains, and its coordinates are consistent with those of the external reference hole. 3) Glass is required.
III. Some special requirements for blind hole boards:
1. blind hole with resin plug: when the size of the buried hole is very large and the number of holes is large, a lot of resin is necessary to cover the buried hole when pinning. To avoid its harm to the thickness of the pin, when required by R&D, the buried hole can be plugged with resin in advance before pinning. The plugging method should refer to the green oil plug hole.
2. When there is a blind hole in the outer layer, a. Because glue will be discharged from the outer layer when the pin is pinned, there must be a glue removal process after the pin; B. Because the surface of the board will be cleaned before the external wet film, there is a plate grinding process, and the organic chemical copper deposit is too thin, only 0.05MIL to 0.1MI, so it is very easy to be ground when the board is ground. Therefore, everyone will add a plating process, thickened copper. Its related process flow is as follows: pin-removing glue-drilling-copper deposit-plate plating-wet film-pattern plating.
3. In addition, PIN-LAM pins will be used when making blind hole boards with high layers, but it should be noted that only when the thickness of the CORE is less than 30MIL, everyone’s equipment can drill PIN-LAM holes, for example, PR4726010, and everyone uses general pins. 4. Regarding blind hole boards and board edges, considering that there are several pins and more processing holes, Therefore, try to keep the edge of the sheet above 0.8 ″. 5. When writing the LOT card, regarding the sub-steps, it is necessary to write the layout structure of the single sub-step as well as the layout structure of the main process in the very requirements, in order to facilitate the following process flow.
