In the process of rapid SMT patch proofing, everyone knows that one of the important links is soldering. If the solder joints are not full of tin, it will have a very serious impact on the performance and appearance of the circuit board. Therefore, when proofing, try to avoid the situation of insufficient tin.
Why is the tin not full during fast proofing of SMT patch?
First, if the wettability of the flux used is not up to the standard when soldering the solder paste, there will be insufficient tin when soldering.
Second, if the flux activity in the solder paste is not enough, the oxidized substances on the china PCB pads cannot be better removed, which will also have a certain impact on the tin.
Third, if the expansion rate of the flux is very high during the fast proofing of Shenzhen SMT patch, there will be a phenomenon of easy cavitation.
Fourth, if the PCB pads or SMD soldering positions are severely oxidized, the soldering effect will also be affected.
Fifth, if the amount of solder paste used during soldering is too small, the soldering will not be full enough, and there will be vacancies. This kind of error will not occur as long as experienced operators are .
Sixth, if the solder paste is not fully stirred before use, and the flux and tin powder are not fully fused, then some solder joints will not be full.
Third, if the expansion rate of the flux is very high during the fast proofing of Shenzhen SMT patch, there will be a phenomenon of easy cavitation.Fourth, if the PCB pads or SMD soldering positions are severely oxidized, the soldering effect will also be affected.Fifth, if the amount of solder paste used during soldering is too small, the soldering will not be full enough, and there will be vacancies. This kind of error will not occur as long as experienced operators are .Sixth, if the solder paste is not fully stirred before use, and the flux and tin powder are not fully fused, then some solder joints will not be full.Third, if the expansion rate of the flux is very high during the fast proofing of Shenzhen SMT patch, there will be a phenomenon of easy cavitation.Fourth, if the PCB pads or SMD soldering positions are severely oxidized, the soldering effect will also be affected.Fifth, if the amount of solder paste used during soldering is too small, the soldering will not be full enough, and there will be vacancies.
In the automated surface mount line, if the circuit board is not flat, it will cause inaccurate positioning, components cannot be inserted or mounted on the holes and surface mount pads of the board, and even the automatic insertion machine will be damaged. The circuit board on which the components are installed is bent after soldering, and the component feet are difficult to cut neatly. The board cannot be installed on the chassis or the socket inside the machine, so it is also very annoying for the assembly plant to encounter the board warping. The current surface mount technology is developing in the direction of high precision, high speed, and intelligence, which puts forward higher flatness requirements for PCB boards that are home to various components.
In the IPC standard, it is specifically pointed out that the maximum allowable deformation of PCB boards with surface mount devices is 0.75%, and the maximum allowable deformation of PCB boards without surface mounting is 1.5%. In fact, in order to meet the requirements of high-precision and high-speed placement, some electronic assembly manufacturers have stricter requirements on the amount of deformation.
The PCB board is composed of copper foil, resin, glass cloth and other materials. The physical and chemical properties of each material are different, and thermal stress will inevitably occur after being pressed together, which will cause deformation. At the same time, in the PCB processing process, it will go through various processes such as high temperature, mechanical cutting, wet treatment, etc., which will also have an important impact on the deformation of the board. In short, the reasons for the deformation of the PCB can be complex and diverse. Distortion or deformation caused by processing has become one of the most complicated problems faced by PCB manufacturers.
The deformation of PCB board needs to be studied from several aspects such as material, structure, pattern distribution, processing process, etc. This article will analyze and explain various reasons and improvement methods that may occur.
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 the problem of 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.
The connection points (vias, 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 are 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.
The weight of the circuit board itself will cause the board to dent and deform. Generally, the reflow furnace will use 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 the board is too heavy If the size of the part or the board is too large, it will show the phenomenon of depression in the middle due to the amount of itself, causing the board to bend.
If you can keep in mind the above-mentioned situations that may cause tin insufficiency when doing SMT PCB assembly fast proofing, then you can effectively avoid the problem of tin insufficiency, so as to avoid scrap and increase investment. The occurrence of the cost situation.
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