As electronic products become thinner and more compact, the size and volume of the PCBs used in these devices are also reduced. This trend drives the advancement of HDI (High-Density Interconnect) technology, resulting in ultra-thin, high-density HDI boards. These boards feature smaller sizes, higher hole density, and more compact traces, resembling a carrier board. As a challenging manufacturing process, HDI boards are characterized by ultra-thinness, miniaturization, high density, and precision, pushing the limits of PCB design and production.
Overview of Ultra-Thin and High-Density Blind Hole Products:
This ultra-thin, high-density HDI multi-layer board is produced through a laminated pressing process using a universal FR4 resin system, semi-cured sheets, and electrolytic copper foil. Key challenges include the lamination of ultra-thin core plates, mechanical and laser drilling, as well as managing the expansion and contraction of the core plates during processing. During production, issues such as plate deformation, uncontrolled thickness, and significant interlayer deviations are common challenges.
Product Information and Lamination Design:
Product Introduction:
Four-layer first-order HDI (1 + 2 + 1).
The finished board thickness is 0.25mm ± 0.025mm.
Minimum mechanical hole size: 0.1mm, with 282,038 holes.
Minimum laser hole size: 0.1mm, with 1,345,698 holes (on both sides).
Individual size: 5 * 5mm, 546 pieces per set;
Critical Control Points:
Internal Drilling:
The total number of holes is 282,038, with a core plate thickness of 0.065mm (without copper). After drilling, the copper thickness is reduced to 7-9 microns. The minimum drilling tool size for the inner layer is 0.1mm, and a custom drilling nozzle is used. Phenolic pads are applied to prevent the lance from causing deformation of the plate.
Lamination Pressure:
The pressing thickness is 0.22mm, with a single piece of 106 P. The layout is 4 panels per layer. Careful control of glue deficiency and shrinkage is essential to achieve the desired laminate thickness and effect.
Laser Drilling:
The laser hole density is very high, with 428,241 holes on the top surface (T) and 917,457 holes on the bottom surface (B). The hole size is 0.1mm, with an outer single-layer thickness of 106 PP and an inner core plate copper thickness of 18μm. Laser energy needs to be carefully controlled to manage laser breakdown and hole quality. Laser effect:
Electroplated Plug Holes and Surface Copper:
Given the 0.25mm thickness of the plate and the outer copper layer thickness not exceeding 18μm, laser holes need to be filled with a baffle.
Soldermask:
The pads are small, and the soldermask must be applied using LDI (Laser Direct Imaging). The surface treatment is performed using a nickel-palladium-gold process.
Product Display:
The thickness of each layer of the product:
The thickness of the final finished plate is 0.247mm:
The appearance of the finished product:
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