From smartphones to the electronic control units in modern vehicles and even to aerospace systems, Ball Grid Array (BGA) packaging plays a crucial role in high-performance electronics. Known for its compact size and pin density, BGA has become a preferred packaging solution for modern electronic products. Even though BGA soldering presents challenges in SMT assembly, we still manage to overcome.
What Makes BGA Packaging Unique?
Ball Grid Array (BGA), is an advanced surface-mount packaging technology where solder balls replace traditional pins, connecting the chip to the Printed Circuit Board (PCB). The design allows for higher pin density in a compact size, enabling more complex circuits in a smaller footprint.
However, the compact nature of BGA also introduces soldering challenges. The fine–pitch solder balls demand extreme precision during assembly. Any deviation can lead to connection failures, impacting overall circuit performance. Furthermore, traditional PCB via techniques often struggle to meet the routing demands of high-density BGA layouts.
Solder Paste Printing: The Foundation of Reliable Joints
Think of BGA soldering as constructing a skyscraper—the foundation must be solid and firm. In SMT assembly, that foundation is solder paste printing.
Solder paste is made of tiny solder powder mixed with flux. The printing process is similar to stencil art on coffee—PCB stencils (metal masks) are placed over the board, and a squeegee spreads solder paste across the aperture, ensuring precise deposition onto the solder pads.
Different application scenarios require the selection of the appropriate type of solder paste. Lead-free soldering has become the mainstream trend in the electronics industry. In addition, there are special types of low-temperature solder paste suitable for specific needs.
However, solder paste printing is not an easy task. If the squeegee parameters are not set correctly, or if there are problems with the solder paste itself, it may lead to various printing defects, such as insufficient solder paste, too much solder paste, bridging and so on.
Reflow Soldering: Mastering Temperature Profiles
Once solder paste is applied, reflow soldering bonds the BGA to the PCB. This process is more than just heating—it’s about precise temperature control to prevent defects.
A typical reflow temperature profile consists of four key phases:
- Preheat – Gradually raises temperature to prevent thermal shock.
- Activation – Flux activates, removing oxides from the surface of the solder pad and solder balls.
- Reflow – Temperature reaches the peak, melting the solder and forming joints.
- Cooling – The solder solidifies to ensure strong mechanical and electrical bonds.
Different PCB materials, component characteristics, and solder paste require tailored temperature profiles.
BGA Welding, Design Optimization and Quality Control: X-Ray Inspection, Via-in–Pad and Defect Analysis
Traditional visual inspection methods are ineffective since BGA solder joints are located beneath the chip. X-ray inspection offers a non-destructive solution, allowing manufacturers to visualize the inside structure of the solder joint and detect potential issues.
Common BGA Soldering Defects:
- Bridging – Unintended connections between adjacent solder balls.
- Cold Solder Joint – Incomplete melting leads to weak connections.
- Voids – Air pockets or trapped inside solder joints reduce reliability.
- Weak Solder Joint – Missing or poorly formed connections.
Case Study and Solution
In the scenario shown below, pin U1_B7 presents challenges due to high-density constraints.
To resolve this, we could redesign the entire routing scheme.
Or we adopt a more direct approach—drilling a via in the pad and routing the trace from another layer. While this method simplifies routing and creates a cleaner layout, it has drawbacks. Drilling vias in pads may affect SMT soldering quality and weaken the pad’s mechanical strength, raising reliability concerns. This is why many PCB designers show hesitation in using this technique.
To tackle this issue, we introduce Via-in-Pad technology, which not only optimizes routing density but also enhances electrical performance and soldering reliability.
Via-in-Pad technology uses a resin-filled and plated-over (resin plug + copper cap) approach. The approach allows vias to be placed directly in BGA pads without additional fan-out traces.
Advantages of Via-in-Pad Technology
- Higher Routing Density – Release more routing space, especially in high-density BGA designs.
- Improved Electrical Performance – Reduces trace length, minimizing inductance and signal delay.
- Eliminates Traditional Via Issues – Eliminates the risk of via pad discoloration caused by solder mask covering. Moreover, it prevents solder ball blowout during BGA soldering due to plugged vias.
- Increased Design Efficiency – A routing task that previously took 7 days may now take just 2 days.
Lead-Free Soldering
To protect the environment and human health, the electronics industry is gradually phasing out lead-based solder and adopting lead-free soldering. The RoHS directive enforces stringent environmental regulations on lead-free processes. However, lead-free solder has a higher melting point and lower wettability compared to traditional lead-tin solder, requiring stricter process control.
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