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May.2021 10
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The causes of PCB board deformation
Introduction
The uneven copper surface area on the circuit board will worsen the bending and warping of the board.
Details
  1. The uneven copper surface area on the circuit board will worsen the bending and warping of the board.
Generally, a large area of copper foil is designed on the circuit board for grounding purposes. Sometimes there is also a large area of copper foil designed on the Vcc layer. When these large area copper foils cannot be evenly distributed on the same circuit board When it is installed, it will cause uneven heat absorption and heat dissipation. Of course, the circuit board will also expand and contract. If the expansion and contraction cannot be done at the same time, it will cause different stress and deformation. At this time, if the temperature of the board has reached At the upper limit of the Tg value, the board will begin to soften, causing permanent deformation.
 
  1. The connection points (vias) of each layer on the circuit board will limit the expansion and contraction of the board.
Today's circuit boards are mostly multi-layer boards, and there will be rivet-like connection points (vias) between the layers. The connection points are divided into through holes, blind holes and buried holes. Where there are connection points, the board will be restricted. The effect of expansion and contraction will also indirectly cause plate bending and plate warping.
 
  1. The weight of the circuit board itself will cause the board to dent and deform.
Generally, the reflow furnace uses a chain to drive the circuit board forward in the reflow furnace, that is, the two sides of the board are used as fulcrums to support the entire board. If there are heavy parts on the board, or the size of the board is too large, It will show a depression in the middle due to the amount of seed, causing the plate to bend.
 
  1. The depth of the V-Cut and the connecting strip will affect the deformation of the jigsaw
Basically, V-Cut is the culprit that destroys the structure of the board, because V-Cut cuts grooves in the original large sheet, so the V-Cut is prone to deformation.
 
  1. Deformation caused during PCB processing.
The reason for the deformation of PCB board processing is very complicated and can be divided into two kinds of stress: thermal stress and mechanical stress. Among them, the thermal stress is mainly generated during the pressing process, and the mechanical stress is mainly generated during the stacking, handling and baking of the plates.