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In the process of BGA chip device repair, setting the appropriate temperature curve is the key factor for the success of BGA chip welding table. Compared with the normal production of reflow welding temperature curve setting, BGA repair process has higher requirements for temperature control. Under normal circumstances, the BGA repair temperature curve can be divided into six parts: preheating, heating, constant temperature, fusion welding, back welding and cooling.
Precautions for setting temperature curve of BGA repair table
1. Currently, there are two kinds of tin commonly used for SMT: one with lead and none without lead. The composition is lead Pb tin, SN, silver AG and copper CU. The melting point of the solder paste with lead is 173℃/, and the melting point of the solder paste without lead is 207℃/. That is to say, when the temperature reaches 183 ℃, the solder paste with lead begins to melt. At present, the widely used is that the temperature rise rate of lead-free chip preheating zone is generally controlled in 1.2~5℃/s(second), the temperature of holding zone is controlled in 140~170℃, the peak temperature of reflow zone is set in 225~235℃, the heating time is 15~50 seconds, and the time from heating to the peak temperature is kept in about one and a half to two minutes.
BGA repair table temperature curve peak setting
2. During welding, due to different definitions of temperature control by each manufacturer and the BGA chip itself due to heat transfer, the temperature transmitted to the tin bead part of the BGA chip will be a certain temperature difference than that at the outlet of the hot air. Therefore, when adjusting the detection temperature, we should insert the temperature measuring wire between BGA and PCB, and ensure that the exposed part of the front end of the temperature measuring wire is inserted. Then adjust the air volume and wind speed according to the needs to achieve uniform and controllable heating purpose. In this way, the heating precision temperature of the BGA repair table is the most accurate. We must pay attention to this method in the operation process.
Common problems in setting temperature curve of BGA repair table
1. The welding paste on the surface of BGA is too much, and the steel mesh, tin ball and planting table are not clean and dry.
2. Solder paste and solder paste are not stored in the refrigerator at 10℃, PCB and BGA are damp and have not been baked.
3. When welding BGA, the PCB support card is too tight, and no gap is reserved for PCB thermal expansion, resulting in plate deformation and damage.
4, the main difference between lead tin and lead-free tin: (lead 173 deg C lead-free 207 DEG C) with lead liquidity is good, lead-free is poor. Harmfulness. No lead is environmental protection, lead is not environmental protection.
5, the bottom of the dark red external heating plate can not be cleaned with liquid substances, you can use dry cloth, tweezers, clean.
6. After the end of the second section (warming section) curve, if the measured temperature does not reach 155℃, the target temperature (upper and lower curves) in the temperature curve of the second section can be appropriately raised or its constant temperature time can be appropriately extended. It is generally required that the detection temperature of the temperature measuring line can reach 155℃ after the end of the second section curve.
7, BGA surface can withstand the highest temperature: lead less than 250℃(standard 260℃), lead-free less than 260℃(standard 280℃). Can be based on the customer's BGA information for reference.
8. If the return welding time is too short, the constant temperature time of the return welding section can be increased moderately, and the difference can be increased by as many seconds as possible.
Although the BGA repair platform temperature curve setting process is more troublesome, but we only need to test once, after saving the temperature curve can be used several times, is a matter of once and for all, we must be patient in the process of setting step by step operation. Only in this way can we ensure that the temperature curve is set correctly when BGA repair table is welding chips, so as to ensure the repair yield.
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