Fundamentals
Definition
A Quad Flat Package (QFP) is a surface-mounted integrated circuit (IC) package featuring a flat, rectangular or square body with "gull wing" leads extending horizontally from all four sides.[1] These leads are bent downward in a characteristic L-shape to facilitate direct attachment to the surface of a printed circuit board (PCB).[1] The primary purpose of a QFP is to enable the mounting of ICs, such as microprocessors and memory chips, onto PCBs using surface-mount technology (SMT).[1] It supports high pin density for electrical connections—typically accommodating dozens to hundreds of leads—while maintaining a low overall profile, which is essential for compact electronic devices like consumer gadgets and automotive systems.[2] This design balances connectivity needs with space efficiency, allowing for denser circuit layouts without significantly increasing board height.[1] The QFP was developed in Japan in 1977 at Hitachi's Musashi Works, initially under the name Flat Plastic Package (FPP), specifically to package multi-terminal large-scale integration (LSI) devices for electronic calculators, including microprocessors (MPUs) and LCD display drivers.[3] Variants such as Low-profile QFP (LQFP) and Thin QFP (TQFP) address specialized requirements for reduced thickness in applications demanding even slimmer profiles.[1]History
The Quad Flat Package (QFP) was invented in 1977 at Hitachi's Musashi Works in Japan, initially known as the Flat Plastic Package (FPP), to facilitate miniaturization in electronic calculators through its compact design and surface-mount capabilities.[3] This early plastic version featured a 14 mm width, 20 mm length, and 2.0 mm thickness, with leads suited for manual soldering, and was primarily applied to calculator microprocessors (MPUs) and liquid crystal display (LCD) driver integrated circuits (ICs).[3] During the 1980s, QFP technology spread across consumer electronics in Asia, driven by Japanese manufacturers like Hitachi and Matsushita Electric, who expanded its use to multi-terminal large-scale integration (LSI) devices such as 4-bit and 8-bit microcontrollers, application-specific ICs (ASICs), and gate arrays in products like camcorders and LCD televisions.[4] Evolution from these initial plastic versions focused on addressing thermal management and higher pin density needs, spurred by growing demand for increased input/output (I/O) in portable devices; for instance, Hitachi introduced the thin QFP (TQFP) in 1988 with a 1.0 mm thickness for memory ICs like dynamic random-access memory (DRAM) and static random-access memory (SRAM), enabling better heat dissipation and compactness.[4] In 1986, the Electronic Industries Association of Japan (EIAJ) outlined QFP standards at the International Microelectronics Conference (IMC), promoting its global standardization as a high-pin-count package.[4] Wider adoption of QFP occurred in Europe and the United States in the early 1990s, coinciding with advancements in surface-mount technology (SMT) that facilitated automated assembly and replaced through-hole methods in mainstream electronics manufacturing.[5] By this period, plastic QFPs with gull-wing leads had become the dominant SMT package for consumer products, supporting pin counts from 40 to over 200 and enabling finer lead pitches down to 0.65 mm.[5] Key milestones included the development of ceramic QFP variants for high-reliability sectors like aerospace, where their hermetic sealing and superior thermal performance provided protection in harsh environments compared to plastic counterparts.[6] By the mid-1990s, QFPs were integrated into personal computers, supplanting earlier pin grid array (PGA) packages, and into communication devices, further solidifying their role in compact, high-performance electronics.[7]Physical Design
Structure and Components
The Quad flat package (QFP) consists of several core components that form its internal structure. At the center is the die, a silicon chip containing the integrated circuit that performs the device's electronic functions. This die is attached to a die pad, typically made from a copper alloy, which serves as a platform for secure mechanical and thermal attachment using adhesive materials.[8] Electrical connections between the die and the package's external leads are established via bond wires, which are thin filaments usually composed of gold or aluminum with diameters ranging from 25 to 50 micrometers. These wires link the bonding pads on the die to the inner leads of the leadframe. The leadframe itself is constructed from copper alloys, such as alloy 194 (C194) or electrolytic tough pitch copper (C110), for plastic QFPs; iron-nickel alloys like Alloy 42 are used for ceramic variants. It is produced through processes like fine etching or stamping to create the precise framework of inner and outer leads. To enhance solderability, the leadframe's outer leads are plated with materials like tin or gold.[9][10][11] The entire internal assembly—die, die pad, bond wires, and leadframe—is protected by encapsulation. For standard plastic QFPs, this involves an epoxy mold compound that provides mechanical strength, electrical insulation, and environmental protection. In hermetic variants, ceramic materials are used for encapsulation to ensure airtight sealing against moisture and contaminants. Internally, the die is bonded to the central die pad, with bond wires extending to the leadframe's inner leads, all fully enclosed by the encapsulant to shield against external factors.[8][9][12] Externally, the QFP features a flat, rectangular or square body with leads exposed along the periphery on all four sides, formed into a gull-wing shape for surface-mount compatibility; unlike some other packages, there are no connections on the bottom surface. This design allows for efficient board mounting while maintaining a low profile.[8]Lead Configurations and Dimensions
The leads of a Quad Flat Package (QFP) are configured in a gull-wing shape, characterized by an L-form that extends outward horizontally from the package body edges before bending downward, enabling reliable surface-mount attachment to printed circuit boards (PCBs).[8] This lead geometry provides mechanical stability and exposes the solder joints for visual inspection post-assembly.[13] The leads are typically formed from etched copper frames plated with materials like tin or gold to ensure solderability and corrosion resistance.[1] Standard QFP dimensions encompass body sizes ranging from 5 mm × 5 mm to 20 mm × 20 mm, with package thicknesses between 1.0 mm and 3.8 mm, accommodating pin counts from 32 to 304.[14] Lead pitch, the center-to-center spacing between adjacent leads, typically ranges from 0.4 mm to 1.27 mm, while lead widths can be as narrow as 0.16 mm to support fine-pitch designs.[1] These parameters adhere to industry standards that balance I/O density with manufacturability, allowing up to 76 pins per side in larger packages.[15] Leads are arranged in a uniform grid array along all four sides of the package, with equal numbers of pins per side in square configurations or balanced distribution in rectangular ones to maintain symmetry and ease PCB routing.[16] Certain QFP variants incorporate an exposed central pad beneath the package for enhanced thermal dissipation and grounding, which connects to the PCB via solder to improve heat transfer.[1] This lead arrangement facilitates high I/O density compared to dual in-line packages, supporting complex integrated circuits in compact footprints.[17]| Parameter | Typical Range | Notes/Source |
|---|---|---|
| Body Size | 5 × 5 mm to 20 × 20 mm | Square or rectangular; larger up to 32 × 32 mm in extended standards[15] |
| Thickness | 1.0 mm to 3.8 mm | Varies by profile (thin, low, standard)[14] |
| Pin Count | 32 to 304 | Balanced across sides[14] |
| Lead Pitch | 0.4 mm to 1.27 mm | Finer pitches for higher density[1] |
| Lead Width | 0.16 mm minimum | For fine-pitch applications[1] |