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Tasks and methods of raw material quality inspection in SMT patch processing
Main tasks: raw material quality judgment, quality problem prevention, quality information feedback, and quality arbitration.
Methods: sensory inspection, tool inspection, and test.
Quality appraisal: According to relevant quality requirements and specifications, pass tests to evaluate the quality and quality level of raw materials.
Prevent quality problems: pass quality inspections to ensure that unqualified products cannot be used and prevent quality problems.
Quality information feedback: through quality inspection, feedback the quality problems of raw materials to the cooperative enterprise, discover the cause of quality problems in time, and provide a basis for quality improvement.
Quality arbitration: When raw material suppliers and recipients have objections or disputes on quality issues, scientific quality inspection and identification methods are used to determine the causes and responsibilities of quality issues.
2. SMT assembly materials include assembly materials such as components, PCBs, solder paste, fluxes, adhesives, and detergents.
3. The main inspection items of components: weldability, lead coplanarity, and performance.
The weldability of SMT components: mainly refers to the weldability of the ends or pins.
Influencing factors: oxidation or pollution of the welding end surface or foot surface.
There are many methods to detect the weldability of parts, and the commonly used methods are the groove infiltration method, the solder ball method, and the wet weighing method.
5. Welding bath infiltration method.
The sample is immersed in the auxiliary flux to remove the remaining auxiliary flux. When visually evaluated, when the sample is immersed in the molten solder bath about twice as much as the actual production solder bath, the sample shows the continuous area covered, or at least various solder compounds. Cover area reaches more than 95%.
6. Weld the ball.
According to the relevant standards, select the appropriate solder ball specifications and place it on the heating head to heat it to the specified temperature.
Place the sample coated with flux on the test position (lead or pin) so that it is immersed in the solder ball at a vertical speed.
After the solder ball is completely immersed, the wire is completely immersed.
From the time point of view, the time for the wire to be completely infiltrated by the solder ball is about 1s, and it is unqualified if it exceeds 2s.
SMT patch processing set Tab label processing parameters
There are many processes in the production process of SMT chip processing that require the installation of processing equipment, the main steps can be summarized into seven steps:
Video camera: Use the printer camera to image the MARK light spot steel network, and then fine-tune the X, Y, θ and other images to make the image completely consistent with the pad image.
Second, the angle between the scraper and the steel mesh: the smaller the angle between the scraper and the steel mesh, the greater the downward pressure. The solder paste can be easily injected into the steel mesh, and the solder paste can also be easily squeezed in. The bottom of the steel mesh is thus bonded together. The angle is generally 45 to 60 degrees. Most of the automatic and semi-automatic printing presses are currently in use.
Pressure: When pressure is needed, pressure is also an important factor. Squeegee pressure management, also known as squeegee depressurization depth, because the squeegee pressure is too small, the squeegee cannot stick to the mesh surface, so when the squeegee is processed, the thickness of the printing material is correspondingly increased. In addition, if the pressure is too small, a layer of solder paste will be left on the mesh surface, which will easily cause glueing defects, such as molding and bonding.
When the rubber cloth density is high, there is an inverse relationship between the rubber cloths. This relationship narrows the gap and reduces the printing speed due to the influence of the flow rate of the rubber cloth. Due to the high speed of the squeegee and the short mesh, the solder paste cannot fully penetrate into the network, which easily causes defects such as incomplete solder paste and missing printing. The printing speed is related to the printing strength, the greater the printing strength, the greater the acceleration. In scraper processing, the speed and pressure control method is to use scraper.
The printing gap refers to the distance from the printed circuit board to the printed circuit board, and it is closely related to the printing gap.
Sixth, the color separation speed of stencil and circuit board: When the circuit board leaves the circuit board after printing, the color separation speed of the circuit board is the color separation speed. In high-density printing, the color separation speed has a greater impact on the printing quality. Advanced smt printing equipment, when it is separated from the solder paste pattern, its iron mesh will have one (or more) small pauses, that is, multi-stage demolding to ensure the printing effect. Excessive soldering adhesive will reduce the bonding strength of the solder sheet, resulting in local adhesion to the bottom of the mesh and the wall of the opening, resulting in print quality problems, such as reduced printing volume, demoulding, etc. Good dispersion, easy to separate from the screen, easy to open holes, good connection state, no glue.
Cleaning method and cleaning frequency: The stencil cleaning is also an important factor to ensure the quality of printing. The gluing method and the number of gluing are subject to the solder paste material, the thickness of the screen and the hole size. Wet washing, one-time, wire drawing and other iron nets are seriously polluted. If it is not cleaned up in time, it will contaminate the surface of the PCB, causing solder paste to remain near the mesh, or even block the mesh in serious cases.
Many smt factories are not able to set detailed parameters overnight, and need to continuously accumulate experience in long-term practice, improve detailed management, and continuously optimize.
