What are the difficulties in proofing PCB multilayer circuit board?

The difficulties in proofing PCB multilayer circuit boards mainly include:

Interlayer alignment: There are many layers in multilayer PCB, and the tolerance of interlayer alignment is usually controlled within 75 microns. Due to the large size of the unit, the change of temperature and humidity in the workshop environment, the inconsistency of different core materials and other factors, the interlayer alignment control becomes more difficult.

Internal circuit fabrication: multilayer PCB board is made of high TG, high speed, high frequency, thick copper, thin dielectric layer and other materials, which puts forward high requirements for internal circuit fabrication and graphic size control. For example, the integrity of impedance signal transmission increases the difficulty of internal circuit manufacturing. In the process of rapid proofing, there are many thin line signal layers, and the probability of detecting loopholes by internal AOI increases; The inner core plate is thin, easy to wrinkle, poor exposure and easy to bend during etching; Most of the high-rise plates are system boards, with large unit area and high product scrap cost.

Pressing manufacturing: In the process of rapid proofing, many inner core plates and prepreg plates are stacked together, which is prone to defects such as sliding plate, delamination, resin gap and bubble residue. In the design of laminated structure, the heat resistance, pressure resistance, adhesive content and dielectric thickness of materials should be fully considered, and an effective pressing scheme for multilayer circuit board materials should be formulated.

Drilling production: there are many layers, and the total copper thickness and plate thickness are accumulated, so it is easy to break the knife when drilling; BGA is dense and the hole spacing is narrow, which leads to the failure of CAF. The thickness of the plate easily leads to the problem of oblique drilling.

These difficulties require the close cooperation of designers, manufacturers and testers to ensure the realization of high-quality multi-layer PCB circuit board samples. In the process of proofing, every step should be strictly controlled to avoid quality problems and production delays.