PCB POWER launched online High Quality Power Stencils

PCB POWER has now decided to start shipping high quality laser stencils for its customers. Well-known for being ultimate in class service and reliability, PCB POWER will now be providing its customers stencils on demand.  The customers would be free to choose the type of stencils (framed or frameless) they want and place an order for the same online. They can also avail the benefit of a separate price calculator having user friendly concept created for this purpose.
Stencils are used in assembly of high reliability surface mount component assembly. For ultimate accuracy, we manufacture our stencils using fine quality steel and ultra accurate cutting technology.
Customers can now conveniently order PCBs along with Stencil. For further details, please login on your account http://login.pcbpower.com/V2/login.aspx
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How Reliable your PCBs are – Laminates Using High Tg Material

Construction methods of Printed circuit boards (PCBs) are essentially similar, although their constituent materials and the intrinsic quality of their surfaces may differ. These differences affect the durability and functionality of the PCB throughout its life and this may be critical to the application.
Essentially, the PCB should exhibit a reliable performance, whether it is in the manufacturing stage, in the assembly process, or in actual use. Apart from the additional costs incurred for correcting defects in the assembly process, there may be failures in actual use, resulting in claims. From this point of view, the cost of a high-quality PCB may be considered negligible.
Over the years, there has been considerable progress in the development of laminates used in the industry, leading to an improvement in the reliability of PCBs. Introduction of lead-free soldering, very high layer count, environmental issues, and electrical concerns have led to placing greater attention to the PCB materials.
To address the above issues, the laminate industry has introduced several products in the market. However, they all come with their own trade-offs, and there is no one perfect laminate to address all the issues. Users need to look at the pros and cons of each PCB laminate, and select the product that best fits their requirements.
Reliability of the PCB actually depends on the proper selection of the material for the laminate. Three parameters are crucial here—the glass transition temperature (Tg), Coefficient of thermal expansion (CTE), and the decomposition temperature (Td).
Glass Transition Temperature (Tg)—This is an important parameter for the base material, as it determines the temperature at which the resin matrix changes over from a firm, non-elastic condition to a soft, elastic one.
                                               Fig. 1: Glass Transition Temperature
The TG value for the base material actually sets an upper temperature boundary, where the resin matrix starts to decompose and subsequently the PCB delaminates. Therefore, Tg is not the maximum operational temperature for the PCB, but rather one the material can endure for only a very short duration.
Coefficient of Thermal Expansion (CTE)—this parameter shows the thermal expansion of the base material of the laminate, especially the absolute expansion in its z-direction. This value is of importance for the stability of vias. With a low CTE-z value, several reliability issues are reduced, such as cracks within the via, corner cracks, and pad lifting. Mostly, materials with a high Tg value also have a low CTE-z.
                                                 Fig. 2: CTE Before and Beyond Tg
                                          Fig. 3: CTE with Low Tg and High Tg Materials
Decomposition Temperature (Td)—this parameter depends on the energy of binding within the polymers in the resin system of the laminate, rather than on the laminate’s glass transition temperature. In the industry, this characteristic is usually indicated at one of two temperatures 260°C or 288°C, and expressed as the time to delamination of the tested material at either temperature. The time to delamination at a certain temperature is a very important indicator of the heat resistance of the lamination, considering the temperature profile for the lead-free solder reflow process often maximizes at 260°C.
Td indicates the temperature at which the base material loses 5% of its weight and is an important parameter of the thermal stability of the base material. Exceeding this temperature causes irreversible degradation and damages the material by decomposition.
Interrelation between the Parameters
Although knowing the individual numbers for each of the three parameters for a laminate is a good reference, their interdependence is more important. Although it is preferable to have a laminate with a higher Tg, a thermal expansion curve of the laminate offers a better understanding. If the thermal expansion curve shows an extremely high CTE beyond the Tg temperature, it reverses the benefits of a high Tg value.
                                                    Fig. 4: Materials with Different Tg
To understand this, consider the parts of the laminate where metals join the epoxy resin, such as copper traces and vias on the PCB. If the difference in the CTE between the two materials is high, there is a danger of the copper peeling away, and vias developing a crack in their barrels, once the temperature crosses Tg.
During lead-free soldering, the reflow temperature is typically 240-260°C, which is well beyond the Tg of most PCB materials. With very high CTE, even high Tg PCB materials will be unable to survive a soldering process. Therefore, a reliable material well suited to lead-free soldering must have a high Tg value along with a minimal transition of CTE values through Tg, followed with a relatively low CTE beyond the Tg value.
It is also important to look at the CTE value of the material in the x-y plane. Ideally, this value should match that of copper, but considering the complexities of laminates, it is much higher. Practically, a CTE value of 70 ppm/°C is satisfactory, although a lower number is better.
Although not much importance is placed on the Td value of a laminate, it can be a good indicator for the performance of a lead-free soldering process. As the temperature rises during the reflow process and approaches the Td, the resulting mass loss can develop stresses within the PCB material, and this can contribute to delamination. Therefore, materials with Td near the lead-free soldering temperatures may be a reliability concern. Although the material may not actually be losing enough mass for decomposition, the loss may be enough to cause a significant stress build-up.
Practical studies indicate materials with Td of 300°C often have problems with lead-free soldering, whereas materials with a Td of 400°C did not. At the same time, materials with lower Td also demonstrate a higher CTE, aggravating the issue at lead-free soldering temperatures.
Understanding Tg, CTE, and Td for a material and their interactions is very important for the reliability of lead-free soldering for a PCB, especially as it also involves the peel strength issues of the PCB at lead-free soldering temperatures.
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Trends in Surface Mount Technology and Its Relevance with PCB Surface Finish

It is necessary to mass-produce electronic circuit boards in a highly mechanical manner for ensuring the lowest cost of manufacturing. Traditional through-hole electronic components with leads did not lend themselves to this approach. Therefore, since the 1980s, virtually all electronics hardware is being mass-produced using surface mount technology (SMT). Compared to the through-hole technology (THT) used earlier, the surface mount devices (SMD) associated with SMT offer several advantages in terms of manufacturability and performance.

                                               Trends in Surface Mount Packaging
Almost all electronic components are available in forms suitable for surface mounting. SMDs do not have long leads that necessitates passing through the printed circuit board (PCB). Rather, they have very short leads that can be soldered directly to the copper pads on the PCB. Manufacturers use different types of SMD packaging, with the evolution tending towards increasing package and pin densities.

                                           Fig. 1: Trends in Surface Mount Packaging
The popular dual in line (DIP) packaging for ICs with two rows of pins for soldering has now diverged into the PGA, QFP, and TSOP type SMD packages. Compared to DIP, these packages have improved on the packaging density enormously. However, modern electronic equipment design demands even higher densities. As a consequence, we now see extremely dense SMD packaging in the form of BGAs, LQFPs, and TCPs. Now, SMD packages are converging towards chip scale packaging (CSP) types, offering better heat dissipation, higher package densities, and increased flexibility.
This trend towards miniaturization is visible for other passive components as well. All types of resistors, capacitors, and inductors are now available in small SMD packages. For instance, although the 0603 and 0402 packages are most commonly used, smaller sizes of 0201 are also available.
Trends in Soldering Techniques for SMT
Most countries have realized the hazards of using the element Lead in electronic equipment, and as a result, the use of lead and tin combination for production and use of solder has almost stopped. Instead, the industry now uses various forms of lead-free solder, although these have more stringent process requirements.
With the advent of new types of SMD packages, the trend in soldering techniques is also evolving. From the commonly used wave soldering for through-hole devices, the trend is towards use of non-contact soldering using infrared and hot gas reflow methods for SMDs.
Trends in Machinery for SMT
Mass production and high mechanization has replaced manual insertion of through-hole components with sophisticated pick-and-place machines for SMD components. These take the form of precision nozzles, intelligent feeder systems, multi-functional mounters, and 3-D molded interconnect devices.
Apart from advances in automated machinery used for SMT, the introduction of special SMD packages such as BGAs has necessitated use of specialized equipment for inspection of PCBs after assembly. Since it is visually impossible to inspect the underside of a BGA chip after it has been soldered, it is necessary to use X-rays to inspect the soldering. With high volumes of production and miniaturization, it is nearly impossible to inspect PCBs manually after assembly. Therefore, the current trend is towards in-circuit testers (ICT) and computerized automated test equipment using high-resolution digital cameras and special algorithms.
Relevance of Surface Finish of PCBs with SMT
The solderable surfaces of a PCB need protection from oxidation while the PCB moves from manufacturing to assembly. Oxidization of the copper surface prevents formation of a good solder joint. Quality of the surface finish affects first pass yield (FPY) and the final product reliability. Primary reasons for this involve non-uniform surface finish and poor solderability. Although there are other known factors for poor FPY, but surface finish issues are the main.
Typical surface finishes manufacturers use are:
  • Hot Air Solder Leveling (HASL)
  • Organic Solderability Preservatives (OSP)
  • Immersion Silver (ImAg)
  • Immersion Tin (ImSn)
  • Electroless Nickel/Immersion Gold (ENIG)
  • Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)
Hot Air Solder Leveling (HASL) is the most common PCB finish, for both lead and lead-free compositions of solder. The process involves application of molten solder to the exposed pads in a vertical or horizontal panel orientation, with excess solder being blown away with a forced hot air knife. The typical thickness of HASL solder on the copper pad ranges from 0.3-1.5 mil, melting at 183°C for lead solder and at 228°C for lead-free solder, with a typical 12-month shelf life.

                                                      Fig. 2: Hot Air Solder Leveling
However, for HDI applications, the HASL process presents a highly variable topography, or inconsistent surface planarity because of the formation of solder beads/balls not conducive to SMT, especially for QFP and BGA packages. In addition, depending on the alloy used for lead-free solder, the HASL process may be aggressive on copper, reducing the shelf life. While the thermal shock may cause warping of the PCB, there can be PTH diameter issues and bridging of fine pitch traces with solder mask residue preventing HASL from flowing. In addition, contamination on the surface of the copper or resin residue on the laminate may cause poor bonding.
Organic Solderability Preservatives (OSP) is a low-cost transparent coating of organic material, which preserves the copper surface from oxidation until assembly. The process involves application in a dip tank with the PCB in a vertical position, or the use of a conveyorized chemical process, which leaves a very thin coating of the material, typically 100-4000 Angstroms thick. Although OSP is a flat, reliable planar surface, well suited to BGA and QFP packages, the shelf life is rather low, being typically 6 months or lower.

                                              Fig. 3: Organic Solderability Preservatives
OSP is difficult to inspect, and does not stand multiple reflows very well. This raises questions of reliability of exposed copper pads after assembly. As OSP is not conductive, ICT test pads need to be soldered.
Immersion Silver (ImAg) is a metallic solderability preservative, and the process deposits 8-15 micro inches of nearly pure silver on the copper surface. Although it provides a flat, planar surface, excellent solderability, and about 6-12 months of shelf life, immersion silver is sensitive to handling, packaging, electrical tests, and suffers from creep corrosion from salt and sulfur in the environment.

                                                            Fig. 4: Immersion Silver
Immersion Tin (ImSn) forms an intermetallic joint with copper to provide a uniform, dense coating with excellent hole-wall lubricity. As it is possible to engineer immersion tin to be non-porous and with very fine grain, it is the top choice for backplane panel assemblies requiring press-fit pin insertions.
However, immersion tin has a shelf life of 6 months, and is sensitive to handling. In addition, processing of immersion tin requires using Thiourea, a carcinogen with environmental issues.

                                                               Fig. 5: Immersion Tin
Electroless Nickel Immersion Gold (ENIG) is a complicated chemical process, involving nickel plating over the copper pad and subsequent gold plating over the nickel. The gold layer prevents the nickel from oxidizing during storage, while also providing low contact resistance, good wetting for solder, and excellent shelf life of typically 12 months. The flat planar surface is well suited for fine pitch devices such as BGA and QFP. Being conductive, ENIG offers good ICT contacts.

                                              Fig. 6: Electroless Nickel Immersion Gold
However, ENIG is an expensive process, with non-wetting issues if the process has not been executed properly. Slow intermetallic growth can result in poor joint reliability and strength.
Electroless Nickel Electroless Palladium immersion Gold (ENEPIG) is another complicated chemical process, involving depositing electroless nickel on the copper surface, followed by a coating of electroless palladium layer, topped with a layer of immersion gold. The triple layer helps to form a superior solder joint with lead-free solder. As the process allows a thinner layer of gold, the process is less expensive when compared to ENIG, although the extra process step offsets this. The flat planar surface suits fine pitch devices such as BGA and QFPs. As the shelf life is typically 12 months, ENEPIG is the fastest growing surface finish.

                               Fig. 7: Electroless Nickel Electroless Palladium Immersion Gold
PCB manufacturers prefer ENIG and ENEPIG to others because of the relative advantages the two techniques offer, although between the two, their advantages vary. ENIG is suitable for SMT, especially for BGA and other fine pitch components. The technology works well for lead-free soldering, and is highly reliable, which is why the flex PCB market prefers ENIG.
On the other hand, ENEPIG has a much wider acceptance and is suitable for multiple types of packages including THT, SMT, wire bonding, press fit, and more. Apart from being suitable for fine-pitch SMD components such as BGA and QFPs, ENEPIG is applicable to PCBs with different manufacturing technologies, requiring higher densities and reliability.

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Url : https://www.pcbpower.com
Email: pcb@pcbpower.com
Phone: +91 7600012414

Online High Quality Power Stencils

PCB POWER has now chosen to begin transporting great power stencils for its clients. Surely understood for being extreme in class administration and dependability, PCB POWER will now be giving its clients stencils on request. The clients would be allowed to pick the kind of stencils they need and put in a request for the same on the web. They can likewise profit the advantage of a different value number cruncher having easy to understand idea made for this reason.

pcb board manufacturing - pcbpower

Stencils are utilized as a part of gathering of high unwavering quality surface mount segment get together. For extreme exactness, we produce our stencils utilizing fine quality steel and ultra precise cutting innovation.


Fore More Details:

Url : https://www.pcbpower.com
Email: pcb@pcbpower.com
Phone: +91 7600012414