INTRODUCTION PACKAGE DESIGN CONSIDERATIONS No. of Electrical Thermal Reliability Testabilityterminals PACKAGE TYPES Through Hole Packaging Surface Mounted Packaging
•What is packaging?•What is the need for packaging?•What are the various packaging requirements?
• Packaging?1. science and the art of establishinginterconnections2. a suitable operating environment for electricalcircuits.•Need for Packaging?1.Supplies wires to distribute signals and power2. Removes the heat generated by the circuits3. Provides physical support and environmentalprotection.
As a rule, application requirements prescribe: 1. The number of logic circuits and/or bits of storage that must be 2. packaged (interconnected), 3. supplied with electric power, 4. kept within a proper temperature range, 5. mechanically supported, and 6. protected against the environment.
1. No. of Terminals - Major cost factor - Dependent on the function of VLSI device - The smallest pin-out memory IC(stream of data can be limited to a single bit) - Larger pin-outs groups of logic circuits(result from a random partitioning of a computer.)
2. Electrical Design Considerations - As a signal propagates, it is degraded due to reflections and line resistance. - Controlling the resistance and the inductance Controls switching noise - Controlling the impedance Controls reflection-related noise - Controlling the capacitive coupling Reduces crosstalk
3. Thermal Design Considerations: - Keep the operating junction temperature low prevents triggering the temperature- activated failure - General recommendation junction temperature < 150°C - Heat transfer : chip surface (by conduction ) package surface the ambient (by convection and radiation)
4. Reliability: - Good thermo-mechanical performance Good reliability - Interfaces are subject to relatively high process temperatures as the device is powered ON/OFF residual stresses are created Reliability problems in the packages.
5. Testability: - Assumption: a zero defect manufacturing. - Rarely practiced because of the high costs. - Several tests are employed to assess the reliability .
• Basic difference between surface mount(SM) andthrough hole(TH) technology• TH: DIP, QFP and PGA•SMT: SOP, PLCC and LCCC• Chip Size Packaging•Multi Chip Moldules
Through Hole: uses Surface Mount: a chip precision holes drilled carrier is soldered to the through the board and pads on the surface of a plated with copper. board. Advantages: Advantages: - a sturdy support for the - smaller component chip carrier. sizes, - resists stresses caused - lack of through holes, by the expansions of - possibility of mounting components at raised chips on both sides of the temperatures. PC board.
A generic schematic diagram showing the difference between the surface-mount technology (upper) and through hole technology.
Dual-in-Line Packages (DIPs): rectangular package with two rows of pins in its two sides. Quad-Flat Packages (QFPs): pins are provided on all four sides. Pin Grid Arrays (PGA): has leads on its entire bottom surface rather than only at its periphery.
Small-Outline Packages (SOPs): has gull-wing shaped leads; Advantage: requires less pin spacing Plastic-leaded chip carriers(PLCCs): Advantage: offer higher pin counts than SOP as J-leaded chip carriers pack denser. Leadless Ceramic Chip Carriers (LCCCs): The conductors are left exposed around the package; Advantage: Uses multilayer ceramic technology which has high thermal conductivity.