/What are the features of Pcb assembled printed circuit boards?
Printed circuit boards used as PCB assembly and interconnects must adapt to the rapid development of current PCB assembly technology. PCB assembly printed circuit boards have become mainstream products of current PCB manufacturers, and almost 100% of PCBs are SMBs, whose function is same as via-hole PCB, but because the SMC/SMD is directly mounted on the SMB in the craft, so its requirements are much higher than that of the plug-in PCB, and the design and manufacturing are much more complicated. Compared with plug-in PCB, SMB has the following main features.
1, High density. Since the number of SMD pins is up to several hundreds or even thousands, the center distance of the pins can reach 0.3mm, so the SMB on the board requires fine lines and fine pitches, and the line width is reduced from 0.2~0.3mm to 0.1mm or even 0.05mm. The double line between the 2.54mm grids has been developed to 4, 5 or even 6 pcs wires. Thin lines and fine pitches greatly increase the assembly density of the SMB.
2, Small aperture. Most metallized holes in SMB are not used to insert component leads, and soldering is not performed in metallized holes. Metallized holes are only used as electrical interconnections between layers, so they should be reduced as much as possible. Small aperture provides more space for SMB. The aperture is changed from 0.5 mm in the past to 0.2 mm, 0.1 mm or even 0.05 mm.
3, Low thermal expansion coefficient . Any material will swell when heated, and the polymer material is usually higher than the inorganic material in expansion aspect, which will cause damage to the material when the expansion stress exceeds the material’s tolerance. Due to the large number and short SMD pins, the CTE between the device body and the PCB is inconsistent, and the device damage caused by thermal stress often occurs. Therefore, the CTE of the SMB substrate should be as low as possible to match the device.
4, High temperature resistance. Today’s SMB mostly require double-sided mounting components, so SMB is required to withstand two times reflow temperatures, and now more lead-free soldering are used, welding temperature requirements are higher, and requires SMB tiny deformation after welding, no foaming, the pads still have excellent solderability, and the SMB surface still has a high smoothness.
The above is the features of pcb assembled circuit board, for more information, please pay attention to www.medicalpcba.com
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