Compared with the characteristics of conventional circuit board products, high-rise circuit board has the characteristics of thicker board, more layers, more dense lines and vias, larger unit size, thinner dielectric layer, etc., and the requirements of inner space, inter layer alignment, impedance control and reliability are more stringent.
1.1 difficulty of interlayer alignment
Due to the large number of layers of high-rise boards, the alignment requirements of each layer of PCB at the customer's design end are more and more strict. Generally, the alignment tolerance between layers is controlled within ± 75 μ M. considering the factors such as large unit size design of high-rise boards, environmental temperature and humidity of graphic transfer workshop, as well as the dislocation superposition caused by the inconsistency of rise and fall of different core board layers, and the positioning mode between layers, etc., the alignment control between layers of high-rise boards is more difficult Big.
1.2 difficulties in making inner circuit
High Tg, high-speed, high-frequency, thick copper, thin dielectric layer and other special materials are used in high-rise board, which puts forward high requirements for inner layer circuit manufacturing and graphic size control, such as the integrity of impedance signal transmission, which increases the difficulty of inner layer circuit manufacturing. The line width and line distance are small, the open short circuit is increased, the micro short circuit is increased, and the qualification rate is low; there are many fine circuit signal layers, and the probability of AOI missing inspection of the inner layer is increased; the thickness of the inner core plate is thin, which is easy to wrinkle and lead to poor exposure, and it is easy to roll the plate when etching through the machine; most of the high-rise plates are system plates, with large unit size, and the cost of scrapping the finished products is relatively high.
1.3 difficulties in pressing
When several inner core plates and semi-cured sheets are superposed, defects such as sliding plate, delamination, resin cavity and bubble residue are easy to be produced in the compression production. In the design of laminated structure, it is necessary to fully consider the heat resistance, voltage resistance, filling amount and medium thickness of the material, and set a reasonable high-rise plate compression program. The number of layers is too many to keep the consistency between the rise and fall control and the size coefficient compensation; the thin insulation layer between layers easily leads to the failure of reliability test between layers. Fig. 1 is the defect diagram of bursting plate delamination after thermal stress test.
1.4 drilling difficulties
The special plates with high Tg, high speed, high frequency and thick copper increase the difficulty of drilling roughness, burr and decontamination. There are many layers, accumulated total copper thickness and plate thickness, and the drilling tool is easy to break; there are many dense BGAs, CAF failure problems caused by narrow hole wall spacing; inclined drilling problems are easy to be caused by plate thickness.
Oct 18, 2019
