Process requirements of SMT patch processing and matters needing attention

568 Published by FASTPCBA 9月 05,2018

Process requirements of SMT patch processing and matters needing attention

I.Regular SMD mounting

Features: low precision of SMT processing, small number of components, mainly resistance and capacitance, or a few special components.

Key processes:

1.Solder paste printing :FPC is positioned on the printing plate by its appearance. It is usually printed by a small semi-automatic printer, or manual printing. However, the quality of manual printing is worse than that of semi-automatic printing.

2.SMT processing stick installation: can use hand stick to install commonly, the individual component with a few high position accuracy also can use hand stick machine to stick to install.

3.Welding: usually re – flow welding process, special cases can also be used spot welding.

II.High precision mounting during SMT processing

Features: the FPC should be marked with MARK for substrate positioning, and the FPC itself should be flat.FPC is difficult to be fixed, consistency is difficult to be guaranteed during mass production, and high requirements for equipment are required.In addition, printing solder paste and paste process control is more difficult.

Key process :FPC fixation: fixed on the pallet all the way from the printing patch to the reflow soldering.The thermal expansion coefficient is required to be small.There are two methods for fixation. The mounting accuracy is 0.Use the method above 65MM

A;The mounting accuracy is 0.Use when below 65MM

B;Method A: the supporting plate is covered on the positioning template.FPC is fixed on the supporting plate with thin high-temperature tape, and then separated from the positioning template for printing.High temperature resistant adhesive tape should be of moderate viscosity, easy to peel after reflow welding, and no residual adhesive on FPC.

Solder paste printing: due to the loading of FPC on the pallet and the high-temperature tape used for positioning on the FPC, the height is inconsistent with the planar of the pallet, so the elastic spatula must be used in printing.The composition of solder paste has great influence on printing effect, so appropriate solder paste must be selected.In addition, the printing template which adopts method B needs special treatment.

Installation equipment: firstly, solder paste printing machine should be equipped with optical positioning system, otherwise the welding quality will be greatly affected.Secondly, FPC is fixed on the pallet, but there will always be some small gaps between FPC and pallet, which is the biggest difference from PCB substrate.Therefore, the setting of equipment parameters has a great impact on printing effect, mounting accuracy and welding effect.Therefore, the installation of FPC requires strict process control.

SMT patch processing

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