Four Steps to Know BGA

Feel dizzy confronted with some short terms such as SMT, LED, CMRR, CCD or even PCB? These short terms make our communications easy, convenient and fast, but they sometimes lead to our quick memory loss about their concept. This article will share details information about BGA.

What is BGA?

Short for Ball Grid Array, its appearance stems from people's expectations for electronic products with numerous functions, high performance, small size and light weight. To reach this goal, the market requires complex yet small size integrated circuit (IC) chip, which can eventually achieve increased packaging I/O density. For this reason, high density low cost packaging methods are in great need, BGA is one of them.
 

BGA is basically a form of surface mount technology (SMT) or a type of surface mount packaging for ICs. Normally, conventional surface mount packages use the packages' sides for connection to achieve limited area for pins' connection. However, BGA package uses underside for connection and more space can be provided for connection, which makes it possible for the high density of PCBs and high performance of electronic products.

Advantages of BGA

1. Highly-effective Use of PCB Space. Using BGA packaging means the fewer components' participation and smaller footprints also help save the space on custom PCBs, which both highly increases the effectiveness of PCB space.
 

2. Increase in Thermal and Electrical Performance. Since the small size of PCB based on BGA packaging, heat can be dissipated more easily. When silicon wafer is mounted on top, most of the heat can be transmitted downwards to the ball grids. When silicon wafer is mounted at the bottom, the back of silicon wafer is connected to the top of packaging, which is considered as one of the best heat dissipation methods. BGA packaging has no pins that can be bent and broken, which makes it become stable enough so that the electrical performance can be ensured on a large scale.
 

3. Increase of Manufacturing Yields Based on the Soldering Improvement. Most BGA packaging pads are relatively big, which makes it easy and convenient to solder on a large area so that PCB fabrication speed increases with manufacturing yields improved. Besides, with larger soldering pads, it's convenient to re-work on it.
 

4. Fewer Damage Leads. BGA leads are composed by solid solder balls that can't be easily damaged in the process of operation.
 

5. Lower Cost. All advantages displayed above contribute to lower cost. Highly-effective use of PCB space provides opportunity to save material, while increase in thermal and electrical performance helps to ensure the quality of electronic components and decrease the chance of defects.

BGA Families

There are mainly three types of BGAs: PBGA (plastic ball grid array), CBGA (ceramic ball grid array), and TBGA (tape ball grid array).
• PBGA. Normally, BT resin/glass laminate is used as the substrate, plastic as the packaging material. Solder balls can be classified into lead and lead-free solder. No other solder is needed to connect the solder balls with packaging body.
• CBGA. CBGA has the longest history among the three types of BGAs. The material of substrate is multi-layer ceramic. Metal cover is soldered onto the substrate by packaging solder in order to protect the chip, leads and pad. High temperature eutectic solder is used as the material of solder balls.
• TBGA. TBGA is a structure with a cavity. There are two kinds of interconnections between chip and substrate: inverted solder bonding and lead bonding.
 

The following table shows advantages and disadvantages comparison between those three types of BGAs.

Step#4: Inspection of BGA

X-ray inspection is widely used to inspect the quality of BGA. With X-rays as its source, it inspects hidden features of target objects or products. Here are the main 4 inspection parameters obtained through X-ray laminography technology:
• Position of Solder Joint Centers: The relative positions of solder joint centers can reflect the positions of electronic components on PCB pad.
• Solder Joint Radius: Solder joint radius measurement shows number of solder in solder joints on a specific layer. The radius measure on the pad layer indicates any change caused in the process of paste screening craft and pad pollution. The radius measurement on the ball level layer indicates the solder joint coplanarity problems about surpassing components or PCBs.
• The thickness of solder on each loop that is obtained with solder joint as a center: Loop thickness measurement indicates the distribution of solder in solder joints. This parameter is used to judge the humidity and existence of voids.
• Deviation from Circular Form. It indicates the uniform of solder distribution around solder joints, autoregistration and humidity.
 

These four parameters inspected are quite significant to determine the integrity of solder joint structure and to understand the performance of each step in the process of the implementation of BGA assembly craft. To know the information provided in the process of BGA assembly and the relationship between these physical inspections is capable of stopping displacement and improving craft so as to eliminate defects. What's more, X-ray laminography inspection can be used to indicate the defects occurring at any step in the process of BGA assembly.