What is HDI overlay?
1. Simple one-time build-up PCB (one-time build-up 6-layer board, laminated structure is (1+4+1)) This kind of board is the simplest, that is, the inner multi-layer board has no buried holes, and it is completed in one press. Although it is a one-time laminated board, its manufacturing is very similar to a conventional multi-layer board once laminated, but the subsequent difference from the multi-layer board is that it requires multiple processes such as laser drilling of blind holes. Since this laminated structure has no buried holes, in the production, the second and third layers can be used as a core board, the fourth and fifth layers can be used as another core board, and the outer layer is added with a dielectric layer and copper. The foil, which is laminated with a dielectric layer in the middle, is very simple, and the cost is lower than that of a conventional primary laminated board.
2. The conventional one-layer HDI PCB printed board (one-time HDI 6-layer board, the stacked structure is (1+4+1)). The structure of this type of board is (1+N+1), ( N≥2, N even number), this structure is the mainstream design of the primary laminated board in the current industry. The inner multi-layer board has buried holes and needs to be pressed twice. This type of primary build-up board has blind holes and buried vias. If the designer can convert this type of HDI PCB into a simple primary build-up board of the first type above, it will be important to both supply and demand. All are beneficial. We have many customers after our suggestion, it is preferable to change the laminated structure of the second type of conventional primary laminate to a simple primary laminate similar to the first type.
3. Conventional two-layer HDI printed boards (two-layer HDI 8-layer board, the stacked structure is (1++1+4+1+1)). The structure of this type of board is (1+ 1+N+1+1), (N≥2, N even number). This structure is the mainstream design of secondary laminate in the current industry. The inner multi-layer board has buried holes and requires three presses to complete. The main reason is that there is no stacked hole design, and the production difficulty is normal. If the buried hole optimization of the (3-6) layer is changed to the buried hole of the (2-7) layer as described above, one press fit can be reduced and optimized Process and achieve the effect of low cost pcb manufacturing. This type is like the example below.
4. Another conventional two-layer HDI printed circuit board (two-layer HDI PCB 8-layer board, the stacked structure is (1+1+4+1+1)). The structure of this type of board ( 1+1+N+1+1), (N≥2, N even number), although it is a secondary laminate structure, but because the position of the buried hole is not between (3-6) layers, but in ( 2-7) Between layers, this design can also reduce the pressing time by one, so that the HDI board of the second layer requires three pressing processes, which is optimized to a second pressing process. And this kind of board has another difficulty to make. There are (1-3) layers of blind holes, which are divided into (1-2) layers and (2-3) layers of blind holes. -3) The inner blind holes of the layer are made by filling holes, that is, the inner blind holes of the second build-up layer are made by filling holes. Generally, the cost of this kind of HDI PCB with the hole filling process is higher than that without the hole filling process. The cost is high, and the difficulty is obvious. Therefore, in the design process of conventional secondary laminates, it is recommended not to use stacked hole design as much as possible, and try to convert (1-3) blind holes into staggered (1-2) blind holes And (2-3) buried (blind) holes. Some experienced designers can adopt this kind of simple refuge design or optimization to reduce the manufacturing cost of their products.
5. Another unconventional two-layer HDI printed board (two-layer HDI PCB 6-layer board, the stacked structure is (1+1+2+1+1)). The structure of this type of board (1+1+N+1+1), (N≥2, N even number), although it is a secondary laminate structure, there are also cross-layer blind holes, and the depth capability of the blind holes is significantly increased, (1 -3) The depth of the blind holes of the layer is double that of the conventional (1-2) layer. Customers of this design have their own unique requirements, and it is not allowed to make the (1-3) cross-layer blind holes into stacks. Hole blind holes (1-2) (2-3) blind holes, this kind of cross-layer blind holes are not only difficult for laser drilling, but also for subsequent copper sinking (PTH) and electroplating. Generally, PCB manufacturers without a certain level of technology are difficult to produce such boards, and the production difficulty is obviously much higher than that of conventional secondary laminates. This design is not recommended unless there are special requirements.
6. The secondary laminated HDI PCB with blind via stacking design, with blind vias stacked above the buried via (2-7) layer. (Secondary build-up HDI PCB 8-layer board, the stacked structure is (1+1+4+1+1)) The structure of this type of board is (1+1+N+1+1), (N≥2 , N even number), this structure is currently part of the industry's secondary laminated panels have such a design, the inner multi-layer board has buried holes, and needs to be pressed twice. The main feature is the stacked hole design, instead of the cross-layer blind hole design in point 5 above. The main feature of this design is that the blind hole needs to be stacked above the buried hole (2-7), which increases the difficulty of production. The buried hole design is in (2-7). -7) Layer, can reduce one lamination, optimize the process and achieve the effect of reducing cost.
7. The secondary laminated HDI PCB with cross-layer blind hole design (the secondary laminated HDI 8-layer board, the laminated structure is (1+1+4+1+1)). The structure of this type of board is (1 +1+N+1+1), (N≥2,N even number). This structure is a secondary laminated board that is difficult to produce in the industry. With this design, the inner multilayer board has buried holes In the (3-6) layer, it takes three presses to complete. Mainly there is a cross-layer blind via design, which is difficult to produce. HDI PCB manufacturers without certain technical capabilities are difficult to produce such secondary build-up boards. If this cross-layer blind via (1-3) layers, optimize the split For (1-2) and (2-3) blind holes, this method of splitting the blind holes is not the method of splitting the holes at points 4 and 6 mentioned above, but staggering the blind holes The split method will realize cheap pcb manufacturing and optimize the production process.
8. Optimization of other laminated HDI PCB boards. Three-layer printed boards or PCB boards with more than three layers can also be optimized according to the above-mentioned design concepts. Complete three-layer HDI boards , The entire production process requires 4 pressings. If the design ideas similar to the above-mentioned primary or secondary laminates can be considered, the production process of primary pressing can be completely reduced, thereby improving the board Piece yield. Among our many customers, there is no shortage of such examples. The laminated structure designed at the beginning requires 4 times of pressing. After the optimization of the laminated structure design, the production of PCB only needs 3 times of pressing. The function that meets the needs of the three-layer laminated board.
