What Is CSP (Chip Scale Package)?According to the IPC/JEDEC J-STD-012 industry standard, a Chip Scale Package (CSP) is a surface-mount integrated circuit package whose overall package dimensions do not exceed 120% of the original die size. The term initially referred exclusively to packaging solutions identical in size to the semiconductor die itself. However, because such packages were rarely achieved in practical manufacturing, the definition was later expanded to the current industry-standard specification.
Chip scale package defines only package size and surface-mount capability and does not mandate any specific manufacturing process or internal structure. Consequently, any IC package that satisfies the dimensional requirements and supports surface mounting may be classified as a CSP. This flexible definition has led to the development of more than 50 different chip scale package variants, with new designs continuing to emerge. As a result, no single standard can be used to evaluate the manufacturability and reliability of all chip scale package technologies.
Basic Manufacturing Process
The manufacturing process for conventional chip scale package devices is highly standardised and relatively straightforward.
First, the semiconductor die is attached to an interposer substrate using epoxy resin. Non-conductive epoxy is typically employed, while conductive epoxy is used when electrical connectivity through the die backside is required.
Next, wire bonding is performed using gold or aluminium wires to establish electrical connections between the die and the interposer. During this stage, wire height and spacing are carefully controlled to minimise the overall package dimensions.
After bonding, transfer moulding is used to encapsulate the device with moulding compound, providing both mechanical protection and electrical insulation for the die and bonding wires. Once the moulding compound has cured, solder balls are attached to the underside of the interposer to create the external interconnection structure.
Finally, package marking is applied, and the completed devices are separated from the lead frame, producing the finished CSP components.
Key Advantages
Ultra-Compact Size and Weight
Utilising a BGA-style interconnection layout, chip scale package significantly reduces package footprint and thickness while lowering overall weight, making it ideal for miniaturised electronic products.
Excellent Manufacturability and Compatibility
Self-aligning solder joints and the absence of bent leads reduce defect rates and manufacturing costs. Chip scale package are fully compatible with standard SMT assembly processes and typically require no modifications to existing production lines. Furthermore, interposer-based designs can accommodate dies of different sizes without changing the package layout.
High Performance and Reliability
Chip scale package combines the performance advantages of bare dies with the protection and reliability of conventional packaging. The package structure enhances device durability and operational stability while supporting high-volume manufacturing through lead-frame-based production. Multiple devices can be integrated onto a single substrate, improving manufacturing efficiency.
Flexible Design Parameters
Chip scale package supports highly customised package configurations, with package pitches ranging from 1.27 mm to 5 mm and thicknesses below 1 mm. Most CSP devices comply with MSL 3 moisture sensitivity requirements and are typically only around 20% larger than the original die size, offering significantly higher packaging precision than traditional package types.
Main chip scale package Structures
Flip-Chip CSP (FCCSP)
FCCSP is the most widely adopted chip scale package technology. The die is mounted face-down onto a substrate or lead frame and connected through solder bumps or copper pillars, eliminating the need for wire bonds.
Because I/O pads can be distributed across the entire die surface, FCCSP achieves smaller package sizes and removes the parasitic inductance associated with bonding wires, resulting in superior high-frequency performance. It is commonly used in applications requiring up to approximately 200 I/O connections and is available with either CUF (Capillary Underfill) or MUF (Moulded Underfill) processes.
Non-Flip-Chip (Face-Up) Package
This is an earlier packaging structure in which the die is mounted face-up.
Its main limitations include poor thermal dissipation, as heat must be conducted through the sapphire substrate, negatively affecting luminous efficiency and operational stability. In addition, the electrodes are located on the light-emitting surface, causing optical obstruction and current crowding. As electrode spacing decreases, the risk of short circuits caused by metal migration increases. Consequently, this packaging method has largely been superseded by more advanced technologies.
Wire-Bonded Package
Wire bonding uses ultra-fine gold or aluminium wires to establish electrical interconnections between the die and the package circuitry.
This technology offers excellent versatility and low manufacturing cost while supporting high-frequency applications exceeding 100 GHz. It is generally divided into gold ball bonding and aluminium wedge bonding and remains widely used in mid-range and cost-sensitive semiconductor devices.
Ball Grid Array (BGA)
BGA is a high-density surface-mount packaging technology that utilises the entire package underside for solder ball placement.
This significantly increases I/O density while shortening internal signal paths, reducing signal delay and improving high-frequency performance. BGA packages are widely used for microprocessors, high-performance chipsets and other advanced semiconductor devices.
Chip-on-Lead (COL)
In COL packaging, the die is mounted directly onto the leads of the lead frame without the use of auxiliary support tape.
The simplified structure enables a smaller package footprint and is well suited to compact, low-pin-count electronic devices.
CSP vs COB Packaging
Both chip scale package and COB (Chip-on-Board) are miniaturised packaging technologies commonly used in sensing devices and camera modules. However, they differ significantly in package structure, manufacturing process, performance characteristics and maintainability.
Chip scale package strictly follows package size specifications, with the package area limited to no more than 1.2 times the die area. Packaging is completed by the semiconductor manufacturer, and the finished image sensor typically includes a protective glass cover over the photosensitive surface to prevent contamination from dust and moisture.
By contrast, COB involves mounting the bare die directly onto a PCB or flexible printed circuit (FPC). It is primarily an assembly process performed by module manufacturers, and the die surface generally lacks a protective glass layer.
From a hardware perspective, COB modules typically achieve lower overall module height and superior space utilisation. In manufacturing, CSP offers higher production precision, faster processing speeds and the ability to rework contamination-related defects, although at a higher cost and with some optical transmission loss. COB provides lower manufacturing costs and maximum space efficiency but generally involves longer production cycles, and defects cannot be repaired once assembly is completed, making after-sales maintenance more challenging.
Relationship between chip scale package and BGA
Chip scale package can be regarded as a miniaturised derivative of BGA technology.
Typical BGA packages feature ball pitches of 1.0–1.27 mm, whereas chip scale package generally employ pitches of 0.8 mm or less and maintain package dimensions within 1.2 times the die size.
BGA is primarily intended for high-pin-count, high-performance and high-power devices such as CPUs and motherboard chipsets, while chip scale package focuses on achieving extreme miniaturisation for consumer electronics applications. The two technologies therefore serve complementary market requirements.
Based on structural design, CSP can be categorised into:
Lead-frame CSP
Rigid interposer CSP
Flexible interposer CSP
Wafer-Level Chip Scale Package (WLCSP)
Applications
Chip scale package technology successfully combines compact dimensions, lightweight construction, low power consumption and high performance, making it ideally suited to portable intelligent electronic products.
Today, chip scale package is extensively used in smartphones, ultra-thin laptops, digital cameras, handheld devices, portable terminals and numerous other miniaturised electronic products, where it serves as a core packaging technology for high-precision, space-constrained applications.
With its exceptional miniaturisation capability, outstanding manufacturing compatibility and highly flexible performance characteristics, chip scale package has become an indispensable packaging technology in modern portable electronics.
Driven by the continued growth of 5G, AIoT and wearable devices, chip scale package technology is expected to evolve towards even thinner, lighter and more reliable solutions, serving as a critical bridge between semiconductor design and end-user applications.
