Issued Date: 2021/10/26
At the end of September this year, Mark Liu, Chairman of TSMC, was interviewed by the media. He made the promise to reduce carbon emissions by 20% by 2030 and achieve net zero emissions by 2050. When the interview was released, it became the focus of the industry. This was not just because of TSMC’s astonishing sales, but also because the reductions of carbon emission by 20% equivalent to a single factory equal the annual carbon emissions of Taipei City. More importantly, because of the close interconnectivity of the semiconductor industry chain, TSMC’s actions will influence every link of the supply chain. Using the 2030 goal as an example, the suppliers who do not comply with TSMC’s demands will most likely lose orders. Therefore, carbon reductions have transformed from an additional action into a necessary matter for corporate survival.
Although the carbon reduction actions of TSMC have rocked the semiconductor industry, Allan Tseng, Vice President of Reliability Engineering Division of iST, stated that several international brands have also set clear carbon reduction targets in recent years, including Microsoft, Google and Apple. The International Standards Organization has also already stipulated two greenhouse gas standards, ISO 14064 for organizations and ISO 14067 for products. Besides carbon reduction standards, another important standard for brands is ISO 50001 for energy management. The main purpose of this standard is to help corporations set energy reduction performance, and the performance must be achieved through a structural method. This requires the cooperation of related supply chains and for these supply chains, the easier method that provides significant results is to change the assembly process.
Regarding the energy savings for assembly processes, the RoHS, passed by the EU in 2003 and officially implemented in 2006, must be mentioned. This directive limits the use of 6 hazardous materials in various equipment and devices. Among these materials, lead (Pb) is the primary material used in the soldering of circuit boards. Therefore, this directive has a substantial impact on electronic devices. Despite the big influence, the directive must still be followed. In the manufacturing process, the biggest difference between leaded and lead-free (Pb-free) is temperature. Solder containing lead can be soldered at 183℃, while lead-free (Pb-free) solder needs to reach 217 to 220℃. The high temperature leads to high energy consumption and can deform the PCB and large components.
LTS Solves the Problems with Lead-free Processes, iST Lowers the Barrier for Entry
Chiahao Chuang, CLR_BLR Engineering Dept. Manager of iST, then pointed out that a common problem during the assembly process is when a good IC is unable to pass testing after being mounted on the board after SMT. The most common problem in this situation is board warpage. He explained that there are many reasons for warpage. iST’s Board Level Reliability (BLR) lab has found that a common reason for the warpage has been a System in Package (SiP) problem. This type of packaging integrates different chips into one package. However, because the different components of the materials and functions have different heat expansion constants, the board will become warped. This is especially apparent for materials that do not change linearly to heat, but changes exponentially to heat. This means that when the temperature reaches a certain level, the degree of bend will increase suddenly. In advanced manufacturing processes, warpage is a common situation. If the amount of warpage complies with the SMT controllable range, then adjustments to the SMT stencil design are possible. Products with greater warpage can also be corrected using the fixture in the manufacturing process.The warpage for larger chips in SiPcan reach several hundred μm. In later assembly stages, the warpage cannot be corrected with stencil design or soldering temperature, and the product will be returned to initial IC design remodification.
In the past, in order to prevent poor soldering due to board warpage, iST’s BLR lab would first use the internal Shadow Moiré simulation to confirm the warpage data and reduce the wasted soldering and short circuit problems through the adjustment of solder printing stencil design and reflow temperature. However, this method can only solve the warpage problem in the final stage. In order to prevent the warpage from reoccurring, the root problem must be dealt with, which is to reduce the manufacturing temperature. Therefore, due to the combination of this need and the aforementioned energy saving trend, Low Temperature Soldering (LTS) technology leapt into the market.
Before talking about LTS, solder paste must be mentioned first. Early solder pasts were mainly made of tin (Sn) and lead (Pb). After the introduction of lead-free regulations, companies began using Sn with bismuth (Bi). However, Sn with Bi will become brittle after soldering, so the companies began introducing various exclusive solder pastes. Currently, LTS primarily uses Sn, indium (In), copper (Cu) and other material combinations. The low temperature of LTS can solve the warpage problem and improve energy savings in the manufacturing process by 40% according to Intel in the iNEMI (International Electronics Manufacturing Initiative) report. Although the benefits are LTS are apparent, changes in the manufacturing process will influence every part of the process. So, without mandatory energy savings in manufacturing in the overall industry, the assembly companies will not change if they are not required to do so.
However, with the changing times, not only are the customers demanding energy savings, the component companies are also changing their methods. The most significant example is the introduction of LTS processes in large CPU and GPU companies. With the pressure from upstream and downstream links in the supply chain, investments in LTS by assembly plants have become necessary. Allan Tseng state that for many companies, LTS is still a new technology. Both component and system companies are still unfamiliar with the technology and market regulations. Therefore, iST and DEKRA iST have separately introduced LTS verification platforms to help different companies to reduce the technological barrier for entry and assist with the smooth shipment of products.
Chiahao Chuang further mentioned that the LTS verification platform of iST is mainly used to test the reliability of components and board levels. The electronics reliability analysis (RA) can be categorized into low strain rate testing and high strain rate testing. Low strain rate testing is mainly aimed at the effect of the aforementioned temperature and other environmental changes on the products. High strain tests responses to collision, such as a mobile phone falling on the ground. In terms of the heat cycle of the low strain, LTS performed better than lead-free (Pb-free) solder pastes.
However, for high strain, the endurance of LTS is slightly worse. Therefore, there will be higher risks for equipment and assembly processes with LTS in the future. For high strain rate testing, including warpage, vibrations, and IC and PCB connection pull and push forces, items closely related to handheld products must be tested. Currently, although handheld devices are not yet required to use LTS, some IC companies have already started investing in R&D. In response to this, iST is already providing complete board level reliability testing services.
DEKRA iST Assists LTS in Optimizing Modular System Product Testing Benefits
Besides components and board levels, LTS also has a relatively large impact on system plants. DEKRA iST will provide testing services related to this aspect. Bruce Liu, Engineering Development Office Senior Technical Manager of DEKRA iST, pointed out that in the iNEMI report, although products using LTS currently account for less than 1%, by 2027, the market share of LTS will reach 20% due to the push for environmental protection in various industries. There are three driving forces for companies to introduce LTS. The first is the aforementioned carbon reduction trend. With the quickening global climate change in recent years, companies in various industries are also accelerating their carbon reduction actions, with LTS being considered one of the best methods for carbon reduction in electronic products. The second is the improvement of yield and product reliability during the manufacturing process. The high temperature currently required by lead-free (Pb-free) solder pastes may cause cracks in motherboards or breaks in IC circuits during the manufacturing process. Additionally, due to the demand for thinner and more compact consumer products, the side effects of temperature will be amplified inside the smaller spaces, which will affect the lifespan of products. The low temperature characteristic of LTS can solves these problems. The third is the optimization of manufacturing efficiency.In order to prevent high temperatures damaging components during soldering, traditional SMT must use wave soldering to solder through-hole electronic parts onto the circuit board. When using LTS solder paste, the low temperature can simultaneously complete the soldering of SMT and through-hole electronic parts, and will not cause heat damage to the components and motherboards. By eliminating a step in the manufacturing process, the goals of assembly cost reduction and process efficiency improvement can be achieved.
How can existing manufacturing processes be transformed into LTS processes? Bruce Liu stated two important points. The first point is that handheld or outdoor products using LTS must pass reliability assurance (RA) and failure analysis (FA). Because LTS is an old concept, new innovation technology, the soldering joint strength on the motherboard and whether it satisfies customer expectations and market needs must be verified through the two methods For RA and FA, DEKRA iST provides thermal stress testing and mechanical stress testing, which are the aforementioned high and low stress tests. Thermal stress testing uses the stress caused by a hot and cold cycle to degrade the soldering joints.Mechanical stress testing uses vibration or drop to test the strength of the soldering joints. These two tests are required test items for brands. Furthermore, by using failure analysis tools, the stress test compares the soldering joint quality before and after the test to ensure that the product complies with the reliable requirements. Bruce Liu said, with DEKRA iST’s past experiences, the performance of LTS under mechanical or thermal stress is generally still not as good as existing high temperature lead-free solder paste. Therefore, companies which produce LTS have attempted to add elemental additions to reach or even surpass the strength of high temperature lead-free pastes.
The second point is for indoor products with lower risks of vibration, drop and high temperature variation; LTS is more suitable because of the better environmental conditions, especially for products with lifespans between 2 to 5 years or products with adhesive protecting the soldering joints internally. If this type of product needs to be used in outdoor environments, the environmental temperature must be below 40℃ and the internal temperature of the product must not exceed 85℃. Additionally, Bruce Liu also suggested that if the solder balls in the components use LTS, it must be treated carefully. When both the solder paste and the solder balls use LTS, the solder joints may easily be induced abnormal hot-tearing through solidified process, causing the failure risk of the product to increase.
Complete Professional Services to Help Corporations Implement ESG
Michael Peng, Inter Connection Eng. Dept. Manager of DEKRA iST, stated that with the driving forces of energy conservation and carbon reduction trends and manufacturing performance, LTS is slowly becoming the focus of the global electronics industry. However, because the technology is rather advanced and there is insufficient data related to the soldering joint reliability and comparison of different low temperature soldering pastes, Taiwanese companies are worried that the various components on assembled motherboards will be incompatible. Therefore, most companies are still waiting to see the developments. However, as mentioned above, the upstream and downstream of the current industry chain have already been activated and the introduction of LTS has become a necessary step. So, companies must accelerate their adoption.
In order to help Taiwanese companies accelerate their adoption of LTS, iST and DEKRA iST have already begun their market deployment, providing LTS testing and verification services for different links in the industry chain, such as components, board levels, and motherboards. Allan Tseng stated that his company and DEKRA iST own the largest reliability assurance laboratory in Taiwan. iST currently leads the world in the reliability analysis and verification of components and board levels. With extensive production capabilities and experience, DEKRA iST is also one of the leaders in the industry for system analysis and testing technologies. Facing various solder paste products launched by different companies in the current market, iST and DEKRA iST can provide professional and objective reports from a third party perspective using their years of experience.
Anton Hsu, Sales Division Assistant Vice President of DEKRA iST, pointed out that consumer products have higher market sensitivity from the perspective of market analysis. Their transformation speeds are also higher. Currently, not only has several laptop, internet connectivity and other large product manufacturers developed LTS strategies, CPU and other component manufacturers have also taken action. As for enterprise equipment, such as servers, because there are more considerations for stability, their transformation is relatively slower. However, LTS has been deemed as an unavoidable trend for the future. Looking at the overall market, LTS will start experiencing large growths in 2022. He suggests Taiwan companies should utilize the many years of experience accumulated by iST and DEKRA iST to choose appropriate partners with professional data. Companies should record and optimize the figures of carbon footprint to implement the ESG goal of energy conservation and carbon reduction.