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BGA Assembly: From Process Steps to Defect Prevention

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In the rapidly advancing landscape of electronics manufacturing, the intricate process of BGA (Ball Grid Array)  assembly plays a pivotal role. Due to its high-density interconnect capability, BGA packaging offers advantages over other approaches.
Learn with ELEPCB, you’ll gain insights into this innovative techniques, including its process, types and challenges for BGA assembly.

What is BGA in PCB?

Ball Grid Array is an innovative surface mount packaging technology that has revolutionized the way electronic components are mounted onto printed circuit boards. 

Unlike traditional through-hole components, BGAs use an array of solder balls placed beneath the component, forming a grid-like pattern.

Typical BGA PCB
Figure 1: Typical BGA PCB

Each solder ball serves as a connection point between the integrated circuit and the PCB. This arrangement not only offers a more compact design but also improves the electrical connection between the chip and the board. The solder balls are typically made of lead-based or lead-free solder, depending on environmental regulations and specific application requirements.

Types of BGA Package

BGA packages can be categorized into several types:
PBGA(Plastic BGA): the most common type, uses plastic substrate
CBGA(Ceramic BGA): uses ceramic substrate, more reliable and not sensitive to moisture
TBGA(Tape BGA): the thinnest BGA package, uses TAB technology to connect ICs
Flip-Chip Ball Grid Array (FCBGA): uses Flip-chip technology, in which the chip is flipped and connected directly to the substrate via solder balls, enhances thermal and electrical performance.
Micro BGA (µBGA): the size of the solder ball and spacing is tiny, suitable for limited space.
types of bga

BGA Package Comparison: Critical Specifications

ParameterPBGACBGATBGAFCBGAµBGA
Pitch Range0.8-1.0mm1.0-1.27mm0.5-0.8mm0.4-1.0mm0.3-0.4mm
SubstratePlasticCeramicPolyimideOrganic/LaminateFlex Tape
Thermal Perf.15-20°C/W8-12°C/W18-25°C/W5-10°C/W22-30°C/W
Moisture Sens.High (L3)None (L0)Medium (L2)Low (L1)High (L3)
I/O DensityMediumMediumHighVery HighExtreme

Step-by-Step BGA Assembly Process

BGA assembly process
BGA Pacakage Process
Ball Grid Array (BGA) assembly involves the integration of semiconductor packaging, ball attachment and surface mounting. Each stage requires a high level of precision to ensure robust electrical connections and long-term reliability. The following sections outline the critical steps of this process, from chip bonding to final reflow soldering.

1. Die Process

Die attach begins the process, in which the silicon chip is mounted on a substrate or carrier with solder or conductive epoxy. Careful die placement precision is needed in order to have proper thermal and electrical connection.

2. Wire Bonding

Following the die fixing, wire bonding binds the chip pads to the substrate’s inner leads using thin gold or copper wires. The thermosonic or ultrasonic bonding methods are in extensive use. This step ensures efficient signal transmission between the substrate and the chip.

3. Overmold / Encapsulation

To protect the delicate wire bonds and die from mechanical stress and environmental exposure, a layer of overmolding or encapsulation (in most cases epoxy resin) is applied. This creates a sealed hard package for ball attachment.

4. Ball Attach Process

Then solder balls are placed on the bottom of the substrate. To every pad, a layer of flux is printed and then precisely located solder balls—usually Sn-Ag-Cu lead-free alloy—are applied. Then, the assembly is heated up in order to re-melt the solder, forming good contacts between the balls and pads.

5. Singulation and Testing

The parts packaged, following reflow, are singulated (cut off panel) and subjected to electrical and visual inspection. Every BGA is tested for continuity, resistance, and short circuiting before shipping for PCB assembly.
bga process

Common BGA Assembly Defects and Their Prevention

While BGA assembly offers a multitude of benefits, it’s not without its share of challenges.
  • Solder Joint Voids
    • Cause: Excess flux, improper reflow profile, or gas trapped during soldering.
    • Solution: Enhance temperature ramp rate and use vacuum reflow or nitrogen environment to prevent voids.
  • Head-in-Pillow (HiP) Defect
    • Cause: Oxidized solder balls or uneven temperature, leading to incomplete wetting.
    • Solution: Maintain component storage environment, inspect for reflow uniformity, and use fresh solder paste.
    • Cause: Improper solder or misplaced placement.
    • Solution: Adjust stencil thickness, optimize volume solder paste, and ensure proper alignment during placement.
  • Cold or Non-wet Joints
    • Cause: Insufficient reflow temperature or unclean pads.
    • Solution: Clean surfaces of PCB, verify flux activity, and have correct reflow profiles.
  • Cracked or Broken Solder Balls
    • Cause: Thermal cycling stress or warpage of the PCB.
    • Solution: Use materials with matched CTE (Coefficient of Thermal Expansion) and control cooling rate to restrict stress.

Case Study: BGA Hot Tear

Cracks were discovered on BGA solder balls. Upon observation:

The solder balls are located above the chip end. The cracks represent delamination between the solder ball and internal substrate layers (between substrate or die attach). This represents internal thermal tearing (internal interface failure caused by thermal stress), distinct from typical PCB pad detachment or solder joint cold soldering.

Cracks appearing at the upper interface of the chip side suggest this phenomenon resulted from stresses generated within the BGA package structure itself during thermal shock. This can be identified as a classic case of “chip-side thermal tearing,” particularly prone to occur in large chips, large packages, and BGAs with thick substrates.

To address BGA thermal tearing:
  • Verify the BGA’s internal structure with suppliers—specifically regarding the presence of cavities or stress relief designs. 
  • Optimize reflow soldering parameters by reducing peak temperatures and extending dwell times to prevent thermal stress accumulation within the package.

Solving BGA Assembly Challenges: ELEPCB's Proven Approach

As electronic devices become more complex and miniaturized, the intricacies of BGA assembly become increasingly critical to address.

Incorporating advanced technology, skilled engineering, and stringent quality control, ELEPCB’s BGA assembly process is a testament to our commitment to excellence. 

Copper plated BGA
Figure 2: Copper plated BGA

Thermal Considerations

Efficient heat dissipation is a hallmark of BGA technology. However, managing heat distribution during the assembly process is crucial to prevent solder joint failures and ensure the long-term reliability of the device. Uneven heating during reflow soldering can lead to thermal stresses that compromise solder connections, resulting in electrical failures.

It’s imperative to carefully control the reflow soldering process to achieve uniform heat distribution and proper solder wetting, ensuring strong and durable connections.

ELE PCB‘s engineering team meticulously reviews the design requirements and layout specifications to ensure optimal BGA placement. Factors such as thermal management, signal integrity, and manufacturability are carefully considered during this phase. Our goal is to create a design that not only meets the project’s technical requirements but also aligns with best practices in BGA layout and assembly.

Inspection and Rework Challenges

The concealed nature of BGA solder joints poses challenges when it comes to inspection and rework. Unlike traditional packages with visible leads, BGA solder joints are hidden beneath the package, making visual inspection difficult. X-ray inspection becomes crucial to assess the quality of solder connections and identify potential defects such as voids, insufficient solder, or misalignment.

Additionally, in cases of faulty connections, reworking BGA packages demands specialized equipment and expertise to avoid damaging neighboring components. 

x-ray inspection
ELEPCB employs X-ray inspection to peer beneath the package and assesses the quality of solder joints, detecting voids, misalignment, or insufficient soldering. Functional testing is also conducted to ensure that the assembled PCB meets performance expectations and functions as intended. Additionally, ELEPCB’s skilled technicians are well-versed in BGA rework techniques, employing precision tools and techniques to rectify any issues without compromising the integrity of the PCB.

Integrity of Solder Balls

BGA assembly involves intricate soldering of numerous small solder balls. Ensuring the integrity of each solder ball and achieving consistent soldering across the entire package can be a challenge. Factors such as solder paste quality, accurate placement, and controlled reflow profiles play a vital role in achieving reliable solder connections. 

ELEPCB places a strong emphasis on using high-quality solder paste, advanced pick-and-place machines, and meticulous reflow soldering processes to ensure uniform and reliable solder connections.

Alignment and Placement Precision

The precise placement of BGA packages onto the PCB is critical for achieving optimal electrical connections. Misalignment, even by a fraction of a millimeter, can result in poor connections or shorts. Advanced automated assembly equipment and accurate placement algorithms are essential to achieve the necessary alignment precision. 

ELEPCB’s automated assembly lines are equipped with cutting-edge technology to ensure accurate placement of BGA packages. We employ state-of-the-art pick-and-place machines, equipped with vision systems that aid in aligning the packages accurately. Automated equipment ensures that each solder ball aligns perfectly with its corresponding pad, minimizing the risk of misalignment and optimizing the electrical connection.
Careful Component Placement in BGA PCB
Figure3: Careful Component Placement in BGA PCB
At ELE PCB, quality is paramount. Our quality assurance team monitors each step of the BGA assembly process to ensure compliance with industry standards and client specifications. From the initial design review to the final inspection, rigorous quality checks are implemented to maintain the highest level of craftsmanship.

Conclusion

BGA PCB assembly has revolutionized electronic manufacturing, enabling compact, high-performance devices across various industries. ELEPCB’s expertise in BGA assembly, backed by advanced technology and a skilled team, ensures the delivery of reliable, high-quality BGA PCBs that drive innovation forward. Contact us today to discuss your BGA PCB assembly needs and witness the future of electronics manufacturing with ELEPCB.

FAQ

A1:Unlike traditional components, BGA solder joints are hidden beneath the package, making visual inspection impossible. X-ray inspection is essential to detect defects like voids, insufficient solder, misalignment, or bridging, ensuring the integrity and reliability of every connection before final testing.
A2: Uneven heating during reflow soldering can cause thermal stress and solder joint failures. Precise temperature profiling using advanced equipment is crucial to achieve uniform heat distribution and proper solder wetting. This ensures strong, durable connections and long-term device reliability

Learn More about BGA:

A Guide to Ball Grid Array (BGA) Packages

Use, types and advantags of BGA package.
Click Here
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What is BGA Electronics in PCB?

Importance of BGA electronics, components, applications and various related performance comparisons.
Click Here
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About Benjamin

Benjamin is the general manager of ELE PCB, a leading PCB design and manufacturing company based in China. He has over 10 years of experience in the PCB industry, and has been involved in various projects.

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