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What Is IC Substrate ?

Integrated circuit substrates have shot to prominence in recent times. It has resulted from the emergence of integrated circuit types such as chip-scale package (CSP) and ball grid package (BGP). Such IC packages call for novel package carriers, something that gets accounted for by IC substrate. As an electronics designer or engineer, it no longer proves sufficient to understand the importance of IC package substrate. You have to comprehend the IC substrate manufacturing process, the role substrate ICs play in the proper functioning of electronics, and its application areas.

IC Substrate

IC substrate is a baseboard type utilized in the packaging of bare integrated circuit chips. The substrate IC proves important in connecting the chip and the circuit board. Integrated circuits fall under a transitional product that serves to capture semiconductor integrated circuit chip, routing to link the chip with the PCB, and safeguard, support, and reinforce the IC chip, thereby giving it a thermal dissipation tunnel.

Integrated circuit substrate plays a crucial role as connectors of the printed circuit boards to the semiconductor chip. It acts as the conduit and thus requires capacity on IC fabricators to provide interconnect densities that surpass those of PCB fabricators during the IC substrate manufacturing process. Consequently, manufacturers will need a possessing proven specialty and solutions in chemical expertise regarding high-density designs.  

Integrated circuit substrates are diverse and fall under different classifications. To comprehend all of this better, we will look at each classification and the various types under each class.

Integrated Circuit Substrates

Integrated Circuit Substrates

Classification by Packaging Types

  • BGA Integrated Circuit Substrate. It is an IC substrate that performs well in electrical and thermal dissipation performance. Since it can radically increase the chip pins, it becomes suitable for integrated circuit packages with pin counts that exceed three hundred.
  • CSP Integrated Circuit Substrate. It is a lightweight single chip package type with a miniaturized scale. The CSP IC substrate mainly gets deployed in telecommunication and memory products having a small pins number.
  • FC Integrated Circuit Substrate. The flip-chip type package features low circuit loss, low signal interference, effective and well-performed thermal dissipation.
  • MCM Integrated Circuit Substrate. The MCM stands for multi-chip module. It is an IC substrate that absorbs chips performing diverse functions housed in a single package. Consequently, the product comes as an ideal solution because of thinness, lightness, miniaturization, and shortness. Naturally, this substrate type cannot perform well in thermal dissipation, signal interference, fine routing, etc., because multiple chips get packaged into one.

Classification by material characteristics

  • Rigid Integrated Circuit Substrate. Primarily constituted of ABF resin, BT resin, or epoxy resin. It has a coefficient of thermal expansion of approximately 13-17ppm/°C.
  • Flex Integrated Circuit Substrate. The IC substrate has PE or PI resin as its primary constituents and features a CTE of 13-27ppm/°C
  • Ceramic Integrated Circuit Substrate. It contains the ceramic materials like Aluminium nitride, Aluminium oxide, or silicon carbide. The ceramic IC has a comparatively low CTE ranging from 6-8ppm/°C

Classification by bonding technology

While the importance of IC substrate cannot get understated, it is impossible to talk about it without touching on IC packaging. Remember, it is one of the prominent classification types of the integrated circuit substrate.

IC packaging refers to the material that contains the semiconductor device. As a package encasing the IC substrate, it protects it against physical damage or corrosion besides allowing for mounting of electrical contacts. It is especially vital in connecting the electrical contacts to the PCB. Diverse design types of integrated circuits packaging systems exist. Considerations for these varied types become important as each possesses distinctive needs regarding their outer shell.  

IC Packaging

It often comes as the last step in semiconductor devices production. At this stage, the semiconductor receives a casing that protects the integrated circuit from detrimental external elements or age-related corrosion. The casing by design protects the block besides promoting electrical contacts, which deliver signals to an electronic device’s circuit board.

The IC packaging tech evolved from the BGA packages of the 1970s when they became popular among EPMs (electronic packaging manufacturers). However, from the onset of the 21st century, fresher versions and options overshadowed pin grid array packages. Such technologies included the small thin outline and the plastic quad flat pack packages. Currently, more advanced packaging technologies exist like the FCBGA (flip-chip ball grid arrays), an upgrade of the land grid array packages.

IC packaging designs

IC packaging designs also have different categorizations dependent on formation. It includes the substrate type and the lead-frame type. While the two form the primary categorization of IC packaging designs, other secondary categorization forms exist. Here, you will find the following.

  • Pin-grid array. It gets deployed in socketing.
  • Dual-inline and lead-frame packages
  • Such packages get used for assemblies that require pins to go through holes.
  • Chip scale package. It is a direct surface mountable single-die package. It has a small area (1.2 times smaller than that of the die)
  • Quad flat pack. It is a leadless package type, though it has a lead frame.
  • Quad flat no-lead. It is a tiny package, close to resembling a chip size and primarily deployed for surface mounting.
  • Multichip package. Also referred to as multichip modules, the package integrates discrete components, semiconductor dies, and multiple ICs onto a substrate. Consequently, such an arrangement makes it a multichip package and resembles a bigger IC.
  • Area array package. It is a type of package that provides maximum performance and conserves space by utilizing any remaining area of the chip’s surface for interconnection.      

You should note that most companies, including RayMing PCB ad Assembly, use the area array packages like the BGA one. It arises because of the need for multichip structures. Such packages and modules present leading options to solutions utilizing the system-on-chip format. If you, therefore, want to get yourself an ideal IC with the correct substrate and packaging, it helps to consider all these before contacting us.

However, we also offer world-class customer care services. You will get guided appropriately if you cannot figure out the best substrate or packaging type for your integrated circuit.

Applications of Integrated Circuit Substrate PCB

IC substrate PCB mainly applies to specific electronic products. Such products have to prove thin, lightweight, and with advanced functions. Therefore, you will find IC substrate PCB on smartphones, tablet PCs, laptops, and networks primarily in medical care, telecommunication, aerospace, industrial control, and the military. In most instances, you will find it as a mini-led PCB, though micro led is one of the IC substrate applications as well.

Most rigid printed circuit boards have transformed through multiple innovations, ranging from multilayer PCB, substrate-like PCBs, or SLPs, traditional HDI printed circuit boards to integrated circuit substrate PCB.

Features of an Integrated Circuit

An IC substrate needs to have specific characteristics that can align with the features of an integrated circuit. Electronic engineers and designers have to understand the attributes of an integrated circuit to select the best IC substrates when designing their ICs. So what are some of these crucial IC features?

  • Small circuit. An integrated circuit is usually miniaturized, and thus the design, installation, and debugging processes need to prove uniform and simple.
  • Cost-effectiveness. All integrated circuits often exhibit higher performance coupled with relatively low costs compared to their discrete components.
  • Reliability. Integrated circuits come highly reliable as a lot of work has enhanced their reliability over the years, especially in their performance and consistency. Soldering joints get reduced significantly in integrated circuits. Additionally, the need for virtual welding is also reduced, making the IC extra reliable.
  • Lower failure. Integrated circuits possess a lesser failure rate compared to ordinary circuits.
  • Energy-efficient. Integrated circuits are also energy efficient as they consume less energy or power, come in smaller volumes and fetch at lower prices.

Such attributes also double up as some of the most vital benefits of integrated circuits. However, it does not stop there. Consideration should also get placed on the IC substrate characteristics, especially when designing your electronic product’s IC.      

Attributes of an IC Substrate

  • Integrated circuits have numerous and diverse features. It includes the following.
  • Light when it comes to weight
  • Fewer lead wires and soldered joints
  • Highly reliable
  • Enhanced performance when other attributes such as reliability, durability, and weight get factored in
  • Small size

Manufacturing Process of IC Substrate PCB

IC Substrate PCB

As already explained, integrated circuit substrate acts as the primary connection between a printed circuit board and the IC chip. It accomplishes this by the network of conductive traces and holes. But what does the manufacturing process of an IC substrate look like?

Manufacturing Steps

  • Copper patterning and plating. This is the first step in the manufacturing process. It involves the copper platting tech and patterning, which correlates to diverse technological aspects like circuit and control compensation technology, uniform control of copper plating thickness, and fine-line fabrication technology.
  • Solder mask. It follows the copper patterning and plating process. The solder mask for integrated circuit substrate PCB consists of hole filling and solder mask printing technologies. IC substrate PCBs have consistently permitted less than ten-micrometer height difference of substrate between solder mask and pad. However, more than fifteen micrometers is not recommendable.
  • Surface finishing. In this step, it is crucial to ensure a uniform thickness of the surface finish. It involves the use of ENEPIG and ENIG surface finishes, which are acceptable across the board.
  • Inspection and reliability tests. It comes as the last step in the manufacture of IC substrate. Here, the integrated circuit substrate has to get tested for reliability besides getting inspected to certify quality. However, the technology deployed in testing reliability and inspection proves different from those utilized in standard printed circuit boards.

However, it is prudent to understand that the manufacturing process of integrated circuit substrate PCB is not straight forward, despite the steps enumerated above. To better bring everything into perspective regarding the fabrication or manufacturing process, we will look into the different technologies involved in-depth.

Technologies Involved in the Integrated Circuit Production Process

Plenty of diverse and advanced technologies get involved in every stage of the IC production process. The technologies help manufacturers ensure high quality, high-capacity, and high precision interconnection products for progressive IC packaging and simultaneously optimize their cost-efficiency and productivity.  

· Direct Imaging Systems

The direct imaging technology solution aims to specifically handle most of the challenging FCBGA (flip-chip ball grid array), FCCSP (flip-chip chip scale package), module, and BGA/CSP (ball grid array/chip scale package) applications. It thus enables fabricators or manufacturers to realize higher yields besides lowering their TCO (total cost of ownership). The technology delivers unmatched results, including fine-line imaging down to about 8µm, greater and high throughput registration accuracy. Such ascertained systems back the modified semi-additive process and semi-additive process, besides other novel substrate processes.

It finds its application in fine-line direct imaging of plate-resist and etch-resist FCBGA), FCCSP, and BGA/CSP.

· Automated Optical Inspection Systems

An automated optical inspection enables high throughput and high-resolution inspection. It harnesses numerous light sources in the inspection of the integrated circuit substrate panel through a solo scan. Consequently, it delivers unparalleled detection precision and supreme production efficiency.

It finds its application in fine pattern inspection of FCBGA and FCCSP integrated circuit substrates.

· AOS or Automated Optical Shaping Systems

The AOS has a range of solutions that deliver the ultimate quality shaping of short defects in top cutting-edge integrated circuit substrate boards. The action of accurately shaping complicated or fine panel defects that might otherwise have gotten scrapped enables integrated circuit substrate manufacturers to enhance the yield drastically besides reducing their scrap. It thus ensures high volumes of high-quality boards. This is a fully automated and easy-to-operate process coupled with high throughput. It, therefore, delivers noteworthy savings when it comes to staffing, complete with a low TCO (total cost of ownership).

It finds its application in the AOS of short defects in FCGBA and FCCSP integrated substrates.

· UV Laser Drilling Systems

The ultraviolet laser drilling ability answers some of the most challenging integrated circuit substrate app questions. It delivers extreme performance besides production yield. The UV-laser drilling system has an incredible beam quality, superior accuracy of 6μm, and a fine via size of 20µm diameter. Therefore, it is ideal for advanced integrated circuit substrate applications like FCBGA. Further, it is boosted to support progressive packaging applications such as embedded die, organic interposers, and LTCC (low temperature co-fired ceramic). It primarily applies in drilling through-hole and blind vias in embedded dies, FCBGA, and LTCC.

· Inkjet or Additive Printing Systems

The technology delivers high accuracy, high productivity, and high-quality printing at low TCOs. It aims to print dams for FCCSP, BGA, and SiP (advanced system in package) modules by design. Consequently, it enables fabricators to save costs and space when limiting underfill leakage by depositing a protective barrier to close off the adjoining die area. The technology also allows selective insulation layer printing like the QFN (quad flat no-lead) package, an integrated circuit substrate, etc. It, therefore, eliminates the costly lithography steps, simplifies the orthodox process, and limits the operational costs. Additionally, it enables a quicker ramp-up and time to the market for fresh or new products.

The additive printing systems technology provides a smart and safe CAM-ready (computer-aided manufacturing) option for 2D and legend barcode package marking. Such markings eradicate the damage risks arising from contact or heat. It provides accurate and uniform material deposition on complex and uneven surfaces, complete with precise pattern alignment at high contrast, high speed, and fine-feature printing.

Design Consideration for Integrated Circuits

If you want to settle for an ideal IC package or IC substrate, it helps to comprehend and consider the various technical details regarding the integrated circuit design. A case in point involves knowing the correct material composition and substrate for your integrated circuit package. Additionally, it is vital to comprehend the difference that exists between the tape and rigid package substrate. Other companies also opt to use laminates as a substitute to select substrates and lead frames, especially those that function properly with metal conductors. So, what design considerations should you focus on?

· Material Composition

An integrated circuit performance relies heavily on its electrical, chemical, material, and electrical makeup. While the laminate packages and lead-frame have functional differences, they both depend on material composition. Lead-frame packages, the predominant format, utilize gold or silver wire-bond finishes attached through the spot-plating method. It simplifies the process and makes it affordable.

Ceramic packages predominantly deploy alloy 42 as the metal type as it functions with the core material. On the other hand, plastic packages prefer copper lead frames to protect the solder joint besides providing conductivity. Certain countries have policies that encourage material consideration as a critical factor on SM (surface mount) plastic packages.

Frequent revisions of the European standards have subjected the lead finish to intense scrutiny regarding the next-level packaging assembly. It has stemmed from the need to get possible replacements for the tin-lead solders that prove simple to apply besides becoming an industry staple. However, fabricators are yet to coalesce around one solution because of widespread competition between suppliers. Therefore, the lead question proves one that will stay unresolved for some time.

Since the 1970s, laminates have emerged as viable options to lead frames in chip-to-board assemblies. Currently, laminates are prevalent in the integrated circuit packaging solutions industry due to their considerable cost-effectiveness when contrasted against ceramic substrates. High-temperature and organic substrates remain among the top and common laminates. Such laminates offer superior electrical attributes besides proving affordable.

· Applicable Substrates

The rise of semiconductor packages and their popularity has prompted an increase in demand for applicable interposers and substrates. A substrate forms an integral part of the integrated circuit package, and it provides the board with mechanical strength besides allowing it to link with external components and devices. The interposer, on the other hand, enables connective routing within the package. It is also ideal to note that the terms “interposer” and “substrate” get used interchangeably in some instances.

· Difference Between Tape and Rigid Package Substrates

Package substrates often come as tape or rigid varieties. Rigid substrates come firm with a defined shape, while the tape substrates prove flexible and slim. At the onset, integrated circuits featured ceramic material in terms of composition, though it currently consists of the organic substrate material.

Whenever a substrate contains a stack of multiple and thin layers that give rise to a rigid substrate, it gets inferred as a laminate substrate. Integrated circuit manufacturing features two predominant and standard laminate substrates in bismaleimide-triazine (BT) and FR-4. An FR-4 comprises epoxy, while the BT comprises of a high-grade resin material.

BT resin’s emergence as a favorite in the industry stems from its low dielectric constant and insulation qualities. BT gets deployed in almost every other substrate when it comes BGAs. Additionally, it also proves adept as a resin option for CSP (chip scale package) laminates. However, many industry players are fabricating new epoxy-blends and epoxy alternatives that should provide a stern competition to the BT. The outcome of this competition will encompass a possible reduction of prices in due course.

Tape substrates come as an ideal alternative to a rigid substrate. It mainly gets constituted by polyimide and other temperature-tolerant and durable materials. The benefits of tape substrates encompass their capacity to carry circuits while moving. Consequently, the flexibility makes it a popular option in mobile devices such as disk drives. Additionally, tape substrates have a low weight that ensures no additional weight to the surface upon which they get applied to.

· Substrates Designed to Assist Metal Conductors

Integrated circuit packages should also have metal conductors capable of routing signals to various interconnecting features. Because of this, the substrate needs to facilitate the process. Substrates often route the output and input signals of the chip to various features in packages. Copper, typically the placement foil, get bonded to the substrate’s laminate to achieve metal conductivity. Nickel or gold immersion layers get applied atop the copper as finishes to stop oxidation and inter-diffusion.

Final Thoughts

IC substrates are crucial for linking the PCB and IC chip in electronics. Because of this, understanding everything you can about them can become the difference when it comes to a successful or faulty IC design for your electronic application. Therefore, consider the aspects discussed when designing your IC for a better outcome.