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This article introduces the technologies related to multi-chip modules. The cost-efficiency demands of consumer electronics have driven the adoption of PCBA MCM technology. For products requiring high-density integration to achieve high performance, miniaturization, and low cost, PCBA MCM offers a range of packaging technologies.
Keywords: multi-chip module, substrate, package, printed circuit board
1. MGM Overview
PCBA MCM is a module consisting of two or more bare chips or chip-scale package (CSP) ICs assembled onto a substrate.
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1. The modules form an electronic system or subsystem. The substrate can be a PCB, thick/thin film ceramic, or a silicon wafer with interconnection patterns. The entire PCBA MCM can be packaged on the substrate, which can also be encapsulated within the package body. The PCBA MCM package may be a standardized component designed for easy installation on a circuit board or a module with embedded electronic functions. All of these can be directly integrated into an electronic system (PC, instrument, mechanical equipment, etc.).
2. MGM Technology
Numerous articles in China detail PCBA MCM technology. In brief, PCBA MCM can be classified into three main types: PCBA MCM-L, which utilizes a sheet-like multilayer substrate; PCBA MCM-C, which employs a multilayer ceramic substrate; and PCBA MCM-D, which incorporates thin film technology. PCBA MCM-L is a high-density PCB technology suited for bonding and PC processes but is less ideal for environments with high reliability and temperature fluctuations. PCBA MCM-C, using multilayer ceramic substrates, is versatile across analog, digital, hybrid, and microwave applications, with wiring widths and pitches ranging from 254 microns to 75 microns. PCBA MCM-D, based on thin film technology, features a substrate of deposited multilayer dielectric, metal layers, and base materials such as silicon, aluminum, alumina ceramic, or aluminum nitride, with line widths of 25 microns, line center distances of 50 microns, and interlayer channels of 10 to 50 microns. Dielectric materials like silicon dioxide, polyimide, or BCB are used to separate metal layers, and thin dielectric layers are necessary with precise interconnection impedances. When using silicon as a substrate, thin film resistors and capacitors can be integrated, and protection circuits (ESD, EMC) can be included.
3. Market Driving Forces of PCBA MCM
The main reasons for opting for PCBA MCM over surface mount integrated circuits on PCBs include:
3.1. Size Reduction
In PCBs with surface mount integrated circuits, the chip area constitutes about 15% of the PCB area, whereas in PCBs with PCBA MCM, the chip area can reach 30-60% or more.
3.2. Technology Integration
PCBA MCM allows for the integration of both digital and analog functions without restrictions. Application-specific integrated circuits can be combined with standard processors/memories, and Si and GaAs chips can be packaged together. Some PCBA MCM configurations also incorporate passive components to minimize mutual interference and offer more flexible I/O options.
3.3. Data Speed and Signal Quality
High-speed components can be placed closer together, enhancing IC signal transmission characteristics. Compared to standard PCBs, PCBA MCM systems have lower total capacitance and inductive load, which are easier to manage. Additionally, PCBA MCM offers better electromagnetic interference resistance than PCBs.
3.4. Reliability and Use Environment
Smaller systems, compared to larger electronic systems, offer improved protection against electromagnetic, water, gas, and other potential hazards.
