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Some PCB technology and numerical introduction.
Some PCB technology and numerical introduction
A conical hole which is cut to allow the flat head screw to be used is called a countersink hole. It can also be called as a conical hole that is cut into a PCB laminate, or a hole created by using a drill. The main purpose is to let
the head of a countersunk screw, once it is inserted and screwed down in the hole, to sit flush with the surface of the laminate. The cone shaped hole, which is cut into the PCB laminate, is a countersink. It is generally used to
permit the tapered head of a screw to sit flush with the top or bottom of the laminate.
It is mainly used, so that the flat head screw can sit flush with the surface to have a clean look and installation. To ensure correct design for manufacturing, most manufacturers require the details of the hole diameter. They
also need to know if the hole is plated or not. Knowing if the hole is plate or not is critical because in some situations an unplated hole may be grounded to the framework, which could cause a problem that would require
plating to correct. Countersinks usually have an 82 degree or a 90 degree angle; however, other angles are possible that the customer would need to provide to the PCB fabricator.
For accurate drilling of countersink holes, the following information is needed:
Below is an illustration which provides an example of a countersink hole
Backdrill is the process of creating vias by removing the stub in multilayered printed wiring boards, to allow signals to flow from one layer of the board to another. It is a special craftsmanship of control depth drilling.
1.Reduce interference of other signal
2.Improve signal integrity
3.Reduce partial plate thickness
4.Reduce the use of blind and buried vias to reduce the difficulty of PCB fabrication
1. Mostly are rigid boards on back
2. Normally used on 8 layers or above
3. Board thickness is over 2.5mm
4. Minimum hold size is 0.3mm
5. Backdrill is 0.2mm larger than the vias
6. Tolerance of backdrill depth+/-0.05MM
Via in pad technology is widely used in small size PCBs with limits space for BGA. the via in pad process allows vias to be plated and hidden beneath BGA pads. it required PCB manufacturer plugged the vias with epoxy
and then plated copper over it,made it virtually invisible.
PCB assemblers don’t like it, but with some designs, if done properly, there can be a number of compelling reasons for putting vias directly in the SMT pads for BGA and QFN packaged components.
1.It can make routing easier with big or fine pitch BGAs
2.It can allow really close placement of bypass capacitors
3.It can help with thermal management
4.It can help with grounding on high-frequency parts
4.Aluminum PCB thermal conductivity
The thermal conductivity of Aluminum Core PCB, is an aluminum substrate thermal performance parameter, which is one of the three major criteria for measuring the quality (the other two properties are the thermal
resistance value and the withstand voltage value ).
The thermal conductivity of the aluminum substrate can be tested after lamination. At present, the high thermal conductivity is generally ceramics, copper, etc. However, the cost of ceramics and copper is high. So
the most widely used is the aluminum substrate,
which is a unique metal-based copper-clad aluminum substrate with good thermal conductivity, electrical insulation and mechanical properties.
The following factors influence the thermal conductivity of Aluminum PCB:
1.The materials of metal substrate, such as the aluminum substrate, as well as copper substrate and ceramic substrate. They are also divided into many kinds, and each of the thermal conductivity varies from alloy to alloy.
2.The material of copper layer in the circuit: Even if the copper is exactly the same, but differs from the different processes.
3.The thermal conductivity of the glue. The better the insulation of the glue is, the worse the thermal conductivity is.
4.The design of the pad in the circuit: Different pad design results in thermal effects.
The hardness and toughness of the substrate determines the overall flatness, and determines the thermal conductivity of the aluminum substrate.
What is the dielectric Constant?
Dielectric constant will vary depending on such factors as material thickness, number of ply’s and resin content. Always consult us for feedback on your proposed stack-up and controlled Impedance trace width and space BEFORE layout. Every PCB
Manufacturer has a different process and will modify trace widths to achieve desired impedance.
The dielectric constant (DK) is an important factor when designing capacitors and in other circumstances where a material might be expected to introduce capacitance into a circuit. The layers beneath etched conductors in
pcbs also act as dielectrics. Dielectrics are used in RF transmission lines.
The dielectric Constant of the material is very important, as this is then used to calculate the required dielectric spacing and track width
Single Ended Impedance tracks looks like the following