PCB Tech - Baking board steps for PCBA board processing

The PCBA board processing and baking method, large-scale PCBs are mostly placed in a flat style, and 30 pieces are stacked. The PCB is taken out of the oven within 10 minutes after the baking is completed, and it is placed flat at room temperature to cool down naturally. Small and medium-sized PCBs are mostly placed in a flat style, with more than 40 pieces stacked, and the number of upright types is not limited. Take out the PCB from the oven within 10 minutes of baking. The components that are no longer used after repairing do not need to be baked. PCBA baking requirements: regularly check whether the material storage environment is within the specified range. Personnel on duty must be trained. If there is any abnormality in the baking process, the relevant technical personnel must be notified in time. Anti-static and heat insulation measures must be taken when touching materials. Leaded materials and lead-free materials need to be stored and baked separately. After the baking is completed, it must be cooled to room temperature before it can be put on line or packaged.

The PCBA board is used in most electrical equipment. It is a magical board. The narrow board is filled with densely packed power electronic devices, helping the electronic equipment to complete various functions. An important part of the PCBA board is the baking sheet. What steps do we have when processing the PCBA board baking sheet? What are the common problems? Let's take a closer look at the "baking steps and common conditions of PCBA board processing".

Before PCBA processing, there is a process that many PCBA manufacturers will ignore, and that is the baking sheet. The baking sheet can remove the moisture on the PCB board and the components, and after the PCB reaches a certain temperature, the flux can better bond with the components and the pads. The welding effect will also be greatly improved. Let me introduce you to the baking sheet process in PCBA processing. PCBA board baking requirements: the temperature is 120 ± 5 degree Celsius, generally bake for 2 hours, start timing when the temperature reaches the baking temperature. Specific parameters can refer to the corresponding PCB baking specifications. PCBA baking temperature and time setting, PCB sealed and unpacked within 2 months of manufacture date for more than 5 days, baking at 120±5 degree Celsius for 1 hour; PCB manufactured date of 2 to 6 months, temperature 120± Bake at 5°C for 2 hours; PCBs with a manufacturing date of 6 months to 1 year, bake at a temperature of 120±5°C for 4 hours; PCBs that have been baked must be processed within 5 days, and unprocessed PCBs need to be baked again 1 It can be online only within hours; PCBs older than 1 year from the manufacturing date can be baked for 4 hours at a temperature of 120±5°C and re-sprayed tin to be online.

In the process of PCBA board processing and welding, the performance of flux directly affects the quality of welding. So what are the common welding defects of PCBA board processing? How to analyze and improve the bad welding? The bad condition is too much residue on the PCB board surface after welding, and the board is dirty. This may be caused by not preheating before soldering or the preheating temperature is too low, the temperature of the tin furnace is not enough; the speed of the board is too fast; the anti-oxidant and anti-oxidation oil are added to the tin liquid; the flux is coated too much; the component feet and the orifice Disproportionately (the hole is too large), which causes the flux to accumulate; during the use of the flux, no thinner is added for a long time. Usually you can pay attention to this problem if you master these points! There is also a bad situation that is easy to catch fire, this should be paid special attention! The wave furnace itself does not have an air knife, which causes the flux to accumulate and drips onto the heating tube during heating; the angle of the air knife is incorrect (the flux is not uniformly distributed); there is too much glue on the PCBA board and the glue is ignited; the board travel speed is too fast (The flux is not completely volatilized and drips to the heating tube) or too slow (the board surface is too hot); process problems (pcba sheet, or the PCBA is too close to the heating tube). Bad condition: Corrosion (green components, black solder joints). Insufficient preheating results in many flux residues and too many harmful residues; the flux that needs cleaning is used, but there is no cleaning after the soldering is completed. For these two reasons, what are the common conditions of most PCBA board processing? In the process of PCBA board processing and welding, the performance of flux directly affects the quality of welding. Bad conditions: connection, leakage (poor insulation), and the other is the unreasonable PCBA board design. Shenzhen Huatao Intelligent Technology Co., Ltd. is a professional manufacturer of PCBA board design! PCB solder mask is of poor quality, easy to conduct electricity, bad phenomena: false soldering, continuous soldering, missing soldering, too little or uneven flux coating; serious oxidation of some pads or solder feet; unreasonable PCB wiring; foaming The tube is clogged and the foaming is uneven, resulting in uneven flux coating; improper operation method when dipping tin by hand; unreasonable chain inclination; uneven wave crest. Bad phenomenon: the solder joints are too bright or the solder joints are not bright, this problem can be solved by choosing bright type or matte type flux; the solder used is not good. Undesirable phenomena: the smoke is big and the smell is big. These are things to pay attention to.

The problem of the flux itself: the use of ordinary resin will cause more smoke; the activator has a lot of smoke and pungent odor; and the exhaust system is not perfect. Unfavorable phenomena: splashing, tin bead technology: low preheating temperature (the flux solvent is not completely volatilized); fast board travel speed, the preheating effect is not reached; the inclination of the chain is not good, there are bubbles between the tin liquid and the PCB, which are generated after the bubbles burst Tin beads; improper operation when immersing tin by hand; humid working environment; problems with PCBA board: the board surface is wet and moisture is generated; the design of the holes for the PCB to run out is unreasonable, resulting in air trapping between the PCB and the tin liquid; the design of the PCBA board is not Reasonably, the parts feet are too dense to cause swelling. Unfavorable phenomena: poor soldering, insufficient solder joints, dual-wave technology is used, the effective components of the flux have been completely volatilized when the tin is passed; the board travel speed is too slow, the preheating temperature is too high; the flux coating is not Uniformity; serious oxidation of the pads and component pins causes poor tin eating; too little flux coating fails to completely wet the pads and component pins; the unreasonable PCBA design affects the soldering of some components. Defects: 80% of the PCBA board solder mask peeling off, peeling or blistering is caused by problems in the PCB manufacturing process: poor cleaning, poor quality solder mask, PCB board and solder mask mismatch, etc.; tin liquid temperature Or the preheating temperature is too high; the number of soldering is too much; when the hand dip tin is operated, the PCBA board stays on the surface of the tin liquid for too long. The above is the bad welding phenomenon and result analysis in the PCBA processing

Precautions for PCBA board baking: When the skin touches the PCB board, you must wear heat-insulating gloves, and the baking time must be strictly controlled, not too long or too short. The baked PCB board must be cooled to room temperature before going online.