Frequently we do provide the bare PCBs. Quality of PCB has the resulting impact to quality of assembly. To prevent the misunderstanding with the PCB order it is necessary to specify all technological details. In below article the brief overview of PCB parameters is given. It can help you effectively optimize your PCB design.
Technological limits
Wire width, isolation gap, drilled hole size
The limit parameters of PCBs provided from our party can be found here. In real life the limit parameters rarely do occur – 42 layers with 50μm wide wires. Most frequently produced PCBs are 1 to 6-layers, less frequently 8 to 14-layers PCBs. The isolation gaps and wires of 125um usually fits to most of designs. Important also is economic point of view and here more layers and fine wires means more costly product. For a better overview of technological classes that correspond to price levels please refer to table below.
Copper thickness and related limits
If larger current should be transferred through PCB the automatic choice is the wider wire or thicker Copper. Thicker copper limits some other parameters like wire/gap width, pad/hole ratio. Technological limits related to Copper thickness are listed in table below.
Basic laminates – Prepreg insulator
Currently there are plenty of basic PCB laminates. The most common one is FR-4. The properties of FR4 fit both to Lead / Lead free technology and price wise it is acceptable. For severe environment condition (heat, cold) the other materials are more suitable.
Below is the brief overview of available materials:
- FR-2 / CEM1 rarely used, low-cost material dedicated for single layer PCBs
- FR-4 (ISOLA E-Cu quality 104, Tg=135°C) most frequently used for single and double layer PCBs
- FR-4 (ISOLA, Tg=150°C) most frequently used for multi layer PCBs
- PCL370HR (ISOLA, Tg=170°C) material for severe environment conditions
- RO4350B (Rogers, Tg>280°C) VF material Er= 3,48 10GHz/23°C
- VT4x (Ventec) material for Aluminium PCBs, used predominantly for LED lamps
- Pyralux AP (Dupont) material for flexible PCBs
Surface finish
The main surface finish of PCBs are HASL, ENIG, OSP, galvanic Gold, chemical Tin and chemical Silver. Each surface finish has specific features. It is worth to consider the right surface finish selection related to design and storage properties:
* expected are controlled storage condition
Color of solder stop mask and component overlay print
The standard color of solder stop mask is green. Besides of green color we offer blue, red, black and white. The color different from green is extra charged.
Ste standard color of component overlay print is white. The other available colors are blue, yellow, red and black.
Further parameters
- Blind and buried via holes
- Plugged via holes in SMT pads
- Impedance check
- Laser dtilled vias with diameter below 100um
- Multilayer boards with metal core
- PCBs with „IceBerg“ technology = 400μm thick Copper together with 35um Copper in the same layer
- Flex PCBs up to 14 layers
Order of PCB should contain:
- Gerber files of all layers including keep out layer in RS274X
- Drill file in Excellon format
- Specification of parameters:
- Number of layers
- Thickness of the board (standard is 1,6mm)
- Color of the stop solder mask (standard is green)
- Surface finish (standard is HASL/ENIG/…)
- Basic laminate (standard is FR-4 Tg135°C)
- Copper thickness (standard is 35um)
- Color of component overlay if required or without (standard is white)
- Other requirements:
- impedance control
- blind / buried vias
- Routing of direct connectors (PCI / AGP / …)
- Direct connector with galvanic gold
- Copper balance
If the board contain component overlapping the border of the board, or is closer to border than 0.5mm, it should be pointed out in documentation. It will help to design the correct panel layout.
