How to set smt soldering circuit board welding temperature profile?

Welding temperature profile setting. Taking BGA (Ball Grid Array) as an example, the setting of the welding temperature curve during reflow soldering is introduced as below.

1. Heating rate. The preheating heating rate v1 mainly affects the volatilization speed of the smt soldering circuit board solder paste flux. Too high temperature is easy to cause the solder (paste) to splash, thus forming a solder ball. Therefore, the general control is 1 °C / s -2 ° C / s.

The rate of weld heating is a key parameter that has a direct impact on some specific weld defects. Too high, it is easy to cause tin beads, tombstones, offset and wicking. General requirements are as low as possible, preferably no more than 2 ° C / s

2. Preheating temperature. There are three main functions of preheating: volatilizing the solvent in the flux; reducing the temperature difference between the various parts of the PCBA of the smt soldering circuit board; and activating the flux.

The preheating temperature T1 is generally 20 ° C ~ 30 ° C below the melting point of the solder paste. Usually, the lead-free process is set at about 150 ° C, and the lead-free process is set at about 200 ° C.

2. Setting requirements for welding temperature. It is desirable that the lower the temperature of the soldering, the better, but it must meet the minimum temperature requirement for soldering, which should be 11 ° C ~ 12 ° C higher than the melting point of the solder paste. The general soldering temperature range is as follows.

Leaded soldering 195°C≤T<230°C (210°C-235°C recommended)

Lead-free solder 228 ° C ≤ T < 245 ° C ( 230 ° C - 245 ° C recommended)

Mixed soldering 220 °C ≤ T < 230 ° C (recommended: 220 ° C - 235 ° C, based on solder and ball fully mixed)

For smt soldering circuit board lead or lead-free process, why should there be a 11 ° C-12 ° C overheating? There are two reasons, one is to ensure that the BGA package completes the second collapse, can self-calibrate the position; the second is to ensure the solder、 solder balls are completely fused and form an IMC