BGA has been widely used in electronic products, but in actual production and application, BGA is mostly packaged in PBGA (PLASTIC BALL GRID ARRAY) plastic. The biggest disadvantage of PBGA is that it is sensitive to moisture. If PBGA absorbs moisture, PBGA will easily produce "popcorn" phenomenon during welding, which will lead to PBGA failure. Because BGA repair is quite difficult and costly, how to improve the quality of BGA in the SMT process has been paid more and more attention by technicians and production factories. This article mainly analyzes the reasons for PBGA failure and quality improvement methods, and provides technical reference for various SMT processing manufacturers.

 

There are different types of BGA, and different types of BGA have different characteristics. Only by deeply understanding the advantages and disadvantages of different types of BGA, can we better formulate a process that meets the requirements of the BGA process, and can better achieve a good assembly of BGA and reduce the process of BGA. cost.

 

First, let's take a look at the classification of BGA: BGA is usually divided into three categories, each of which has its own unique characteristics, advantages and disadvantages:

 

1. PBGA (PLASTIC BALL GRID ARRAY) plastic package BGA

 

The advantages are:

 

① It is thermally matched with the epoxy resin circuit board.

 

②Solder balls participate in the formation of solder joints during reflow soldering, and the requirements for solder balls are loose.

 

③When mounting, it can be centered by the edge of the package.

 

④ Low cost.

 

⑤ Good electrical performance.

 

Its disadvantages are: it is sensitive to moisture and the density of the solder ball array is lower than that of CBGA

 

2. CBGA (CERAMIC BGA) ceramic package BGA

 

The advantages are:

 

①The reliability of package components is high.

 

②The coplanarity is good, and the solder joints are easy to form, but the solder joints are not parallel to each other.

 

③ Not sensitive to moisture.

 

④ High packaging density.

 

Its disadvantages are:

 

① Due to the different thermal expansion coefficients and poor thermal matching with the epoxy board, solder joint fatigue is the main failure mode.

 

② It is difficult to align the solder balls at the edge of the package.

 

③The packaging cost is high.

 

3. TBGA (TAPE BGA) carries BGA

 

The advantages are:

 

①Although there is local stress in the chip connection, the overall thermal match with the epoxy board is better.

 

② Mounting can be done through the edge alignment of the package.

 

③It is the most economical packaging form.

 

Its disadvantages are:

 

① Sensitive to moisture.

 

② Sensitive to heat.

 

③ Multiple rounds of different materials have an adverse effect on reliability.

 

Here we only focus on the shortcoming of PBGA being sensitive to moisture, and discuss methods to prevent BGA from failing due to moisture absorption in the relevant process links of the actual production process.

 

Acceptance and storage of PBGA

 

PBGA is a moisture-sensitive component. It is packaged in vacuum when it leaves the factory, but it is easy to damage the vacuum package during transportation and turnover, resulting in moisture in the component and oxidation of the solder joints. Therefore, when the component enters the factory for acceptance, the packaging state of the component must be As an inspection item, strictly separate vacuum-packed and non-vacuum-packed components. Vacuum-packed components should be stored according to their storage requirements and used within the shelf life. Non-vacuum components should be stored in a low-humidity cabinet as required to prevent PBGA Moisture absorption and pin oxidation. At the same time, it is controlled according to the principle of "first in, first out" to minimize the risk of component storage.

 

Selection of dehumidification method for PBGA

 

Damp PBGA should be dehumidified before production. BGA dehumidification usually has two types: low-temperature dehumidification and high-temperature dehumidification. Low-temperature dehumidification uses a low-humidity cabinet for dehumidification. Dehumidification is time-consuming, usually at 5% humidity, it takes 192 hours. High-temperature dehumidification uses an oven for dehumidification, and the dehumidification time is relatively short. Usually under the condition of 125 degrees Celsius, it takes 4 hours. In actual production, after high-temperature dehumidification of those non-vacuum-packed components, they are stored in a low-humidity cabinet to shorten the dehumidification cycle. It is recommended to use low temperature dehumidification instead of high temperature dehumidification for the PBGA whose humidity card shows that the humidity exceeds the standard. Because the temperature of high temperature dehumidification is high (greater than 100 degrees Celsius) and the speed is fast, if the humidity of the component is high, it will be due to the rapid vaporization of moisture. lead to component failure.

 

Control of PBGA at the production site

 

When PBGA is used in the production site, after the vacuum-packed components are unpacked, the humidity card on the package must be cross-checked. If the humidity mark on the humidity card exceeds the standard, it cannot be used directly and must be dehumidified before use. When receiving non-vacuum-packed components at the production site, the humidity tracking card of the material must be checked to confirm the humidity state of the material. Non-vacuum-packed components without a humidity tracking card cannot be used. At the same time, strictly control the use time and environment of PBGA on site. The use environment should be controlled at about 25 degrees Celsius, and the humidity should be controlled within 40-60%. The use time of PBGA on site should be controlled within 24 hours. PBGA exceeding 24 hours must be Repeat the dehumidification process.

 

PBGA rework

 

BGA rework usually adopts BGA rework station (BGA rework station). If the PCBA with PBGA is reworked on the production site, if it is placed for a long time, the PBGA will easily absorb moisture and the humidity state of the PBGA will be difficult to judge. Failure and scrapping in mid-term makes BGA ball placement and reassembly futile.

 

Of course, there are many processes and reasons that lead to BGA failure in the SMT process, such as ESD, reflow soldering, etc. In order to reduce the failure of BGA in the SMT process, comprehensive control in many aspects is required. For PBGA, the process links related to moisture absorption of components are often ignored in actual production, and the problems are relatively hidden, which often cause many obstacles for us to improve the process and improve the quality of the process. Therefore, for the shortcomings of PBGA that are sensitive to moisture , in the production process, starting from the above aspects and taking effective countermeasures can better reduce the failure of PBGA, improve the quality of PBGA process, and reduce production costs