ABF, are you facing the enemy?

 When chips ran out last year, Samsung, TSMC, Intel and AMD all focused on one material: ABF (Ajinomoto Build-up Film). And all these stories, from a original do monosodium glutamate enterprise flavor of the beginning.

 According to the 1970s, the group began to explore the application of umami condiment by-products. We know that some of these substances have excellent material properties and can potentially be used in resins and coating agents in the electronics industry. Processors are getting smaller and faster, and printed circuit board manufacturers need better insulation to maintain performance. By 1996, a CPU manufacturer had approached the group to develop a thin-film insulator using amino acid technology. This ultimately promoted the birth of the ABF onboard plate.

 As you can see, advances in circuit integration enable a CPU composed of nanoscale electronic circuits. These circuits must be connected to the millimeter-scale electronic components in the electronic device and system. Of course, this can be achieved by using a laminate plate of a CPU composed of multilayer microcircuits. And ABF facilitates the formation of these micron-scale circuits because its surface accepts laser processing and direct copper plating. Today, the ABF is the basic material for forming a circuit that guides electrons from nanoscale CPU terminals to millimeter-scale terminals on printed carrier plates.

The existence of ABF makes chip miniaturization possible. However, as the chips continue to develop, ABF also faces new challenges.

 ABF, be on one's guard for all possible dangers

 In principle, ABF acts as a bed in the device package, a multi-layer microcircuit connecting the PCB and the nanoscale CPU.

 One key component of the ABF substrate based on it is the capacitor, which is used to decoupling and occupy both sides of the substrate.

anandtech The report also said that modern chips are usually mounted on thin-spaced carrier plates (FPS: fine pitch substrates) and then placed on multi-layer high-density interconnect (HDI: high-density interconnect) carrier plates. Today's CPU / GPU HDI plates use Ajinomoto Build-up Film (ABF), which combines organic epoxy, scleroer and inorganic particulate fillers. ABF is easy to use, enabling high density spacing (thus achieving high density metal wiring), with sufficient to meet the insulation performance of modern chips, high rigidity, high durability and low thermal expansion.

 Zhuang Gui-yi of Taiwan Institute of Engineering Research also wrote that ABF carrier board material is dominated by Intel in the 1990s, which is used for the production of advanced carrier board such as overlay structure and assembly process, and can be made into IC packaging with thinner lines, suitable for high count and high transmission. Its plate core structure is still retained in glass fiber cloth preimmersed resin (FR-5 or BT resin) as the core layer (Core Substrate), then add layer material (Build up Materials) superposition way increase layer number, on the basis of double core, do the symmetrical layer, but the upper and lower layer structure, to the original preimmersed glass fiber cloth pressing copper foil plate, and on the ABF film layer to replace plating copper, as shown in the figure. In this way, the overall thickness of the carrier can be reduced, and the difficulties encountered by the original glass fiber resin carrier can be broken through.

However, as the industry shifts to small chip design, the importance of packaging is increasing, thus creating a new demand for packaging materials.

"Because these multi-small chip designs will be more power-intensive (and therefore hotter), and a higher density of metal writing is required due to the expanded memory and I / O interface. The increase in power demand imposes additional pressure on the peripheral substructure of the circuit. The search for new materials for the core component of chips in the semiconductor industry has been a hot topic for years.”

anandtech Said in the report. In this case, glass is a new target for many manufacturers to explore, because glass is considered to be harder and has multiple advantages over organic resin-based carrier plates, but the bonding between glass and copper (or other metal wires) remains a major challenge in bonding.

 But many manufacturers have already taken a big step forward.

 Glass, is expected to take over?

 Japan's Dai Nippon Printing (DNP) has demonstrated a new development of semiconductor packaging —— glass core carrier (GCS: Glass Core Substrate) —— is said to solve many of the problems caused by ABF.

 DNP claims that its HDI carrier with a glass core has superior performance compared to an organic resin based carrier. According to Dai Nippon, more refined spacing is achieved with glass core carrier plates (GCS), thus enabling extremely dense wiring because it is harder and less likely to expand at high temperatures. The schematic of the DNP display even omitted thin-spaced carrier plates entirely from the package, suggesting that this part may no longer be needed.

 DNP also said in the report that its glass core carrier plate can provide a high aspect ratio of high glass through-hole (TGV) density (compatible with FPS). In this case, the aspect ratio is the ratio between the glass thickness and the through-hole diameter. As the number of holes passes increases and the proportion increases, the processing of carrier plates becomes more difficult and maintaining rigidity becomes more challenging.

 From the introduction of DNP, we can see that its developed glass carrier plate has an aspect ratio of 9 and ensures adhesion to achieve fine spacing compatible wiring. The company said that with very few GCS thickness limitations, there is a great freedom in maintaining the balance between thickness, warping, stiffness and smoothness."We also have new proprietary manufacturing methods that enhance the adhesion between glass and metal, which is difficult to achieve with traditional technology, and which also helps them achieve fine spacing and high reliability."The DNP is also stressed.

 In addition to DNP, South Korea's SK Group Absolics is also optimistic about the opportunities brought by glass. Because they believe that glass has a high heat resistance, so they see it as a reformer of semiconductor packaging. Absolics Said, with the performance of microprocessing has reached the limit, the semiconductor industry is actively using heterogeneous packaging, but the existing semiconductor carrier must be called silicon intermediary layer intermediate carrier connected to the semiconductor chip, and built-in passive components of glass carrier can be integrated under the same size more chip, power consumption is also reduced by half. It is worth mentioning that Absolics also received investment in application materials from major equipment manufacturers in the United States.

 In addition, the glass factory Corning is also optimistic about the opportunity of glass in the load board.

 The new initiatives in semiconductor packaging creates the demand for new material solutions, they wrote in a paper. Great efforts have been made to extend the mediation layer technology for 3D-IC stacking. Multiple solutions are being developed to meet some of these needs, including conventional mediation layers using a variety of commonly used materials and fan-out wafer level packaging (FOWLP), which has become a common consideration in trying to achieve low cost.

 In addition, the surge in mobile devices and the Internet of Things (IoT) has led to increasing requirements for RF communications. These requirements include the introduction of more frequency bands, smaller / thinner package sizes, and the need to save power to extend battery life when introducing new features. Glass turns out to be the * solution to these challenges because glass has many characteristics that support the above initiatives, including high resistivity and low electrical loss, low or adjustable dielectric constant, and adjustable thermal expansion coefficient (CTE).

 Corning says that one of the important challenges of 3D IC stacking is reliability due to CTE mismatch, and glass provides an excellent opportunity to manage the warping of 3D-IC stacking while optimizing CTE. The following figure illustrates the challenges of stacking carriers with multiple CTE in mediation layer applications. The left image schematically shows the Si chip installed on the Si intermediary layer, and then installed on the onboard board. A CTE mismatch causes a failure when the carrier plate experiences a temperature cycle.

However, if the glass intermediary layer with CTE between glass and organic matter is used instead of the Si intermediary layer, this warping can be better managed and improved reliability, as demonstrated by the work of the Georgia Institute of Technology Packaging Research Center (PRC), as shown on the right of the figure above.

 Write at the end

 We must admit that the status of ABF onboard board cannot be shaken in the short term, as we can also see from the statistics and prediction of QYR. According to their statistics, the global ABF substrate market sales reached $4.368 billion in 2021 and is expected to reach $6.529 billion in 2028, with a compound annual growth rate (CAGR) of 5.56% (2022-2028).

 Intel and AMD can also be seen as a barometer of ABF.

 Intel, for example, was trouble last year because of a shortage of ABF. To this end, Intel announced that its Vietnam Assembly and Testing (VNAT) plant will now internally connect capacitors to both sides of the ABF substrate. This change will allow Intel to effectively eliminate the degree of dependence on external suppliers in the ABF manufacturing process. According to Intel, the result is 80% of the faster chip assembly; AMD has also tied long contracts to multiple vendors to ensure ABF supply.

But, like the ongoing story in the industry, nothing is static.