With the development of electronic technology, electronic components are moving towards miniaturization and high-density integration. BGA components have been more and more widely used in SMT assembly technology, and with the emergence of u BGA and CSP, the difficulty of SMT assembly is getting more and more difficult, and the process requirements are getting higher and higher. Due to the difficulty of BGA rework, achieving good welding of BGA is a subject for all SMT engineers.

BGA storage considerations:

The BGA component is a highly temperature-sensitive component, so the BGA must be stored under constant temperature and dry conditions. Operators should strictly follow the operating process to avoid the components being affected before assembly. Generally speaking, the ideal storage environment of BGA is 200C-250C, and the humidity is less than 10% RH (better protection with nitrogen).

In most cases, we will notice the moisture-proof treatment of the BGA before the package of the component is opened. At the same time, we should also pay attention to the time that the component package cannot be exposed during the installation and soldering process to prevent The components are affected and the quality of the components is reduced or the electrical properties of the components are changed.

The following table is a classification of temperature sensitivity. It shows the corresponding time for components to be installed and soldered once the sealed moisture-proof packaging is opened during assembly. Generally speaking, BGA belongs to the temperature sensitivity level above 5.

Table 1 Humidity-sensitive temperature levels

Level Time Time
1 Unlimited ≤30 ° / 85% RH
2 one year ≤30 ° / 60% RH
2a around ≤30 ° / 60% RH
3 168 hours ≤30 ° / 60% RH
4 72 hours ≤30 ° / 60% RH
5 48 hours ≤30 ° / 60% RH
5a 24 hours ≤30 ° / 60% RH
6 According to label regulations ≤30 ° / 60% RH

 

If the components are stored under nitrogen, the use time can be relatively extended. The effect of dry nitrogen approximately every 4-5 hours can extend the air exposure time by 1 hour.

During the assembly process, we often encounter situations where the component package cannot be used within the corresponding time after it is opened, and the exposure time exceeds the time specified in Table 1. To make the components have good solderability, we recommend baking the BGA components. Under baking conditions: The temperature is 1250C, the relative phase humidity is ≤60% RH, and the baking time is shown in Table 2.

Finding the Optimal Baking Temperature for BGA Components to Ensure High-Quality SMT Assembly

The baking temperature should not exceed 1250C, because the high temperature will cause the metallographic structure of the joint between the solder ball and the component, and when these components enter the stage of reflow soldering, it will easily cause The disconnection causes SMT assembly quality problems, but we will think that it is caused by the quality problems of the components themselves. However, if the baking temperature is too low, it will not play a role in dehumidification. When conditions permit, we recommend that the components be baked before assembly, which is beneficial to eliminate the internal moisture of the BGA, improve the heat resistance of the BGA, and reduce the impact of the components on the components due to the thermal shock caused by reflow soldering. The BGA components are taken out after baking and allowed to cool for half an hour before assembly operations can be performed.

Table 2 Baking time

Package Thickness Humidity sensitivity level Baking time
≤1.4MM 2a 4 hours
3 7 hours
4 9 hours
5  10 hours
5a 14 hours
≤2.0MM 2a 48 hours
3 48 hours
3 48 hours
3 48 hours
3 48 hours
5a 48 hours
≤4.0MM 2a 48 hours
3 48 hours
3 48 hours
3 48 hours
3 48 hours
5a 48 hours