IC Package Substrate (IC Package Substrate, referred to as IC carrier board, also known as package substrate) is the key carrier in the packaging and testing process. It is developed on the basis of PCB related technologies and is used to establish an The signal connection of the IC substrate can also protect the circuit, fix the circuit and dissipate the waste heat.

IC substrates are used in mainstream packaging technologies. Semiconductor chip packaging has gone through several generations of changes, and the packaging technology is classified into DIP packaging (dual in-line packaging technology), SOP packaging (small outline packaging), QFP packaging (small square planar packaging), PGA packaging (pin net grid array packaging technology), BGA package (solder ball array package), SIP package (system-in-package). The iteration and upgrading of technology make the current packaging area and chip area close to 1.

Taking BGA (Ball grid array) package as an example, it is a high-density packaging technology, which is different from other packages where the chip pins are distributed around the chip. The number of I/Os accommodated increases. BGA packaging has become one of the mainstream packaging technologies due to its high yield, good electrical characteristics, and suitability for high-frequency circuits. On the basis of BGA, high-density IC packaging methods such as CSP, MCM and SIP are gradually derived. Advanced packaging technology caters more to the characteristics of miniaturization, complexity and integration of integrated circuits. IC substrates are widely used in mainstream packaging technology due to their high precision, high density, miniaturization and thinning.

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In short, the IC substrate is the key substrate for the advanced packaging of integrated circuits, the "special" PCB. As a high-end PCB, IC carrier board has the characteristics of high density, high precision, miniaturization and thinning.

IC substrates have a wide variety of applications and can be classified according to packaging methods, processing materials and application fields:

(1) According to the packaging method, IC substrates are divided into BGA packaging substrates, CSP packaging substrates, FC packaging substrates, and MCM packaging substrates.

(2) According to the classification of packaging materials, IC substrates are divided into hard packaging substrates, flexible packaging substrates and ceramic packaging substrates. Rigid packaging substrates are mainly made of BT resin or ABF resin, and their CTE (coefficient of thermal expansion) is about 13 to 17ppm/°C. Flexible packaging substrates are mainly made of PI or PE resins with a CTE of about 13 to 27ppm/°C. Ceramic package substrates are mainly made of ceramic materials such as alumina, aluminum nitride or silicon carbide, which have a relatively low CTE of about 6 to 8ppm/°C.

(3) According to the classification of application fields, IC substrates are divided into memory chip packaging substrates, micro-electromechanical system packaging substrates, radio frequency module packaging substrates, processor chip packaging substrates, and high-speed communication packaging substrates.

The parameter requirements of IC substrates are much higher than that of general PCB and HDI. Taking line width/line spacing as the measurement index, conventional IC substrate products can reach 20μm/20μm, and high-end IC substrate linewidth/line spacing will be reduced to 10μm/10μm, 5μm/5μm, while the line width of PCB products with ordinary performance /Line spacing is 50μm/50μm or more.

From HDI to SLP to IC substrate, perhaps IC substrate is very suitable for SiP technology.

As we all know: SiP is system-in-package technology, which is a packaging technology in which multiple active or passive electronic components with different functions are integrated in one package to achieve a basically complete function and form a system or subsystem.

But for SiP, due to the very high density of wiring inside the system-in-package, ordinary PCB is difficult to carry; while the number of layers of IC substrate + low line width is more in line with the requirements of SiP, and it is suitable as a packaging carrier for SIP.

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There are two IC substrate manufacturing processes, namely SAP (semi-additive method) and MSAP (modified semi-additive method), which are used for products with a production line width/line spacing less than 25 μm and a more complicated process flow. The production principle of SAP and MSAP is similar. The brief description is to coat a thin copper layer on the substrate, then carry out graphic design, then electroplate the copper layer with the required thickness, and finally remove the seed copper layer. The basic difference between the two process flows is the thickness of the seed copper layer. The SAP process starts with a thin layer of electroless copper coating (less than 1.5um), while MSAP starts with a thin layer of laminated copper foil (greater than 1.5um).

The subtractive method is a PCB manufacturing method, which is briefly described as electroplating a layer of copper on the copper clad board first, protecting the lines and via holes, etching away the unnecessary copper skin, and leaving the traces in the lines and via holes. copper. The most obvious defect of the subtractive method is the high side erosion, that is, the copper layer will also etch the side during the downward etching process, which limits the fineness of the subtractive method. Therefore, the minimum line width/spacing of the subtractive method can only be 50 μm. When the line width/spacing is less than 50 μm, the subtractive method cannot be used due to the low yield.

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The material composition of the IC substrate includes metal materials such as copper foil, substrate, dry film, wet film, and copper ball gold salt.

One of the main raw materials for IC substrates is copper foil. The electrolytic copper required for IC substrates is ultra-thin and uniform copper foil, with a thickness as low as 1.5 μm. Its price is higher than that of ordinary electrolytic copper foil, and its processing is difficult.

Another raw material for IC substrates is the substrate, which accounts for 35% of the cost. The main materials of the substrate are BT material, ABF material and MIF material respectively.

(1) BT resin

BT resin was developed and researched by Mitsubishi Gas Chemical Company in Japan in the 1970s. The main raw material is bismaleimide triazine resin, which is modified by adding epoxy resin, PPE and allyl compound to improve the thermosetting property of BT resin. BT resin has many advantages such as heat resistance, moisture resistance, low dielectric constant, and low dissipation factor. It is used to stabilize dimensions, prevent thermal expansion and contraction, and improve equipment yield. The disadvantage is that the hardness is high, it is difficult to wire, and it cannot meet the requirements of thin lines. BT substrates are used in products such as LED packaging chips, mobile phone MEMS chips, and memory chips.

(2) ABF

The Chinese name of ABF is Ajinomoto stacked film, which is developed by Intel and is monopolized by Japan Ajinomoto Corporation. The ABF material can be used as an IC carrier board with thinner lines and suitable for high pin count and high transmission. It is applied to large high-end chips such as CPU, GPU and chipset. The copper foil of the ABF substrate can be directly attached to the ABF to make the circuit, and there is no need for a thermocompression process. ABF has become the standard material for FCBGA packaging.

(3) MIS

MIS uses a unique packaging material with finer wiring capabilities, better electrical and thermal performance and smaller appearance for ultra-thin, high-density detail packaging. Different from traditional substrates, MIS contains one or more layers of pre-encapsulated structures, and each layer is interconnected by electroplating copper to provide electrical connection during the packaging process. MIS is currently developing rapidly in the market fields such as analog, power IC and digital currency.