Four major causes of board bending and warping

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Four major causes of board bending and warping [Copy link]

SMT is the surface mount technology. During the manufacturing process, the solder paste is heated and melted in a heated environment, so that the PCB pads are reliably combined with the surface mount components through the solder paste alloy. We call this process reflow soldering. When the circuit board undergoes reflow soldering, it is easy for the board to bend and warp. In serious cases, it may even cause empty soldering and tombstone formation of components.

What are the causes of board bending and board warping during PCB manufacturing? Let's discuss it today. The causes of each board bending and board warping may be different, but they can all be attributed to the stress applied to the board being greater than the stress that the board material can withstand. When the stress on the board is uneven or the ability of each part of the board to resist stress is uneven, the board will bend and warp. The following are the four major causes of board bending and board warping.

1. Uneven copper surface area on the circuit board will aggravate board bending and warping.

Generally, a large area of copper foil is designed on the circuit board for grounding. Sometimes, the Vcc layer is also designed with a large area of copper foil. When these large areas of copper foil cannot be evenly distributed on the same circuit board, it will cause uneven heat absorption and heat dissipation. Of course, the circuit board will expand and contract with heat. If the expansion and contraction cannot be simultaneous, different stresses will be caused and deformation will occur. At this time, if the temperature of the board has reached the upper limit of the Tg value, the board will begin to soften and cause permanent deformation.

2. The weight of the circuit board itself will cause the board to sag and deform

Generally, reflow furnaces use chains 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 too heavy parts on the board, or the size of the board is too large, it will appear concave in the middle due to its own weight, causing the board to bend.

3. The depth of the V-Cut and the connecting strip will affect the deformation of the panel

Basically, V-Cut is the culprit that destroys the structure of the board, because V-Cut is to cut a V-shaped groove on the original large piece of board, so the V-Cut area is prone to deformation.

4. The connection points (vias) on each layer of the circuit board will limit the expansion and contraction of the board

Most of today's circuit boards are multi-layer boards, and there are rivet-like connection points ( via) between layers. The connection points are divided into through holes, blind holes and buried holes. The places with connection points will limit the expansion and contraction of the board, and will also indirectly cause the board to bend and warp.

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How to solve these board bending and warping problems during reflow soldering?