Layer misregistration in PCB and its effects on signal propagation
Layer misregistration is one of the common issues in PCB manufacturing processes. In addition to physical limitations of manufacturability (large via pad/anti-pad), it may also have impact on the electrical performance of signal lines running through via fields with anti-pad openings. In order to quantify its effects on signal propagation, comprehensive test vehicles were designed, measured, and analyzed. Significant increases in layer-to-layer crosstalk and common-to-differential mode conversion were observed, when corresponding layers were misaligned. The results helped understand the mechanisms, validate modeling methodology, and define design rules.
PCB Pin Area Wire Modeling Based on Representative Layer 2D Misregistration
In the printed circuit board (PCB) pin area wire modeling the 1D worst-case layer-to-layer misregistration has been used for many years. However, in practical situation, the PCB layer misregistration scenario is usually 2D and much different from the 1D geometric worst-case. As the system signal bit rate increases rapidly, the effect of PCB layer misregistration should be predicted accurately to avoid either over-design or under-design. In this paper, we search for the representative 2D misregistration based on worst case crosstalk power sum from all adjacent aggressor wires. In the search, either the Monte Carlo method or the Half-Tolerance Boundary Scan method is applied to an N-pair pin area wire structure for a partial 2N-port differential port S-parameter model calculated from one differential port excitation only at the crosstalk victim port. After search, the full 4N-port S-parameter matrix are calculated based on the representative 2D misregistration obtained from the worst case crosstalk power sum search. This final model is exported to a regular Touchstone file and can be qualified for passivity and causality criterion. A practical example is given to show the procedure of this approach. The crosstalk power sum by this PBC layer 2D misregistration method is compared with that by traditional geometric worst-case 1D misregistration method. The simulation results show the effectiveness of the new method to provide a more practical and more representative PCB pin area wire model taking into account more practical layer misregistration sienario.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.