BGA REWORK|SMT Technology

Since the late 1990s ball grid array (BGA) packages have been gaining as a preferred package style for several reasons. Their IO density compared with the previous high density ultra fine pith quad flat packs (QFPs) is such that they have shrunk the necessary footprint on the PCB by a factor of 50%. If we lump the BGA style of package, a high density IO with solder balls for the interconnection in with its stacked version counterpart the POP then this increase in density approaches nearly 100%. The ability to get more done in less space along with shorter trace spacing and length requirements for board layouts using this package style have allowed boards to be clocked at much higher rates

thereby increasing processing speed. In addition the reliability of the placement of BGAs has been high as initially the tin lead solder balls “self centered” on the pads during reflow. Lastly the reliability

of BGA packages has been increased with the use of underfills, the use of specialty flex solder balls and even solder columns with integrated springs.

The increased use of BGAs and the underlying trend of ever-smaller package sizes, finer pitches and their placement on to ever denser printed circuit boards has led to greater and greater challenges in BGA rework. In addition to these challenges there are many others that have made the job of BGA rework technicians more and more difficult. One of the trends in making BGA rework more difficult is their ever-increasing usage in handheld device. Due to the drop test requirements of these products

in many cases the BGAs and other higher density devices need to be underfilled. Underfilled BGAs have the challenge of the tacky material “squirt out” causing solder shorts underneath the BGA. In

addition, the tacky nature of this material tends to lift pads as well as destroying the underlying solder mask underneath he BGA. This makes the BGA rework even more challenging. The ever-thinning device packages of BGAs cause the packages to warp. This too makes BGA rework difficult.

While large packages with large-sized pitches placed on sparsely populated printed circuit boards made BGAs simple to remove and replace, BGA rework today requires a greater level of machine sophistication. With pitches down in to the 0.3mm areas and package sizes routinely under 10 x

10mm placement with a vision system using a highly precise and repeatable XY motion system is required. Placement accuracies for today’s BGA rework need to be in the less than a 1mil tolerance

range. In addition with the lead free packages the rework system now require sophisticated temperature control with programmable multi zone bottom heaters, nitrogen capability and low flow rates at the air nozzle. In addition to the rework equipment set the inspection equipment needs to be of a higher capability. X-ray inspection equipment with very small spot sizes is a requirement for BGA inspection post BGA rework. The ability to measure the sphericity of the solder balls, the solder ball diameter, the ability to shoot through RF shields as well as higher density ground planes is now a necessity for the x-ray equipment requirements for BGA rework. Also the endoscope is a necessity for checking the ball collapse, the surface of the BGA ball post reflow, the wetting action as well as other attributes is important in BGA rework.

In addition to the equipment requirements for modern day BGA rework, the skill level, dexterity and process knowledge of the rework technicians working on BGA rework is even more demanding today. The BGA rework technician needs to understand reflow profiles in order to deal with printed circuit boards with a high density of ground planes. The BGA rework technician must also understand flux chemistries and how this impacts the kind of cleaning which can be done underneath the device. The BGA rework technician must also be able to understand how a variety of conformal coatings can be removed from the PCB as well as underneath the BGA. BGA rework technicians must also understand how device which neighbor the BGA to be reworked can or could be impacted by the BGA rework process profile.

As BGA packages have become more widely-accepted the BGA rework process has become more difficult. This has meant that both the equipment used in BGA rework as well as the technicians doing the rework have had to become more sophisticated.

Solder wire and paste feature| SMT Technology

Solder wire and paste feature| SMT Technology

Solder voiding is present in the majority solder joints and is generally accepted when the voids are small and the total void content is minimal. X-ray methods are the predominate method for solder void analysis but this method can be quite subjective for non grid array components due to the two dimensional aspects of X-ray images and software limitations. A novel method of making a copper “sandwich” to simulate under lead and under component environs during reflow has been developed and is discussed in detail. This method has enabled quantitative solder paste void analysis for lead free and specialty paste development and process refinement. Profile and paste storage effects on voiding are discussed. Additionally an optimal design and material selection from a solder void standpoint for a heat spreader on a BCC (Bumpered Chip Carrier) has been developed and is discussed.

Solder voids in solder joints are a common occurrence in SMT assemblies. Their origins are not well understood but are typically faulted as a failure of the solder fillet to thoroughly expel flux remnants during the reflow process. The amount of solder voiding can vary significantly within an assembly, between different flux formulations, solder alloys, board and component metalizations. Reflow profiles as well as stencil aperture designs can often affect the overall level of voiding.

Adding to the mystery of solder voiding is a lack of quantitative measurement tools in the industry with few exceptions. BGA void analysis software is one of these exceptions. This software uses gray level pixel analysis to determine the perimeter of the solder sphere and the internal perimeters of the voids. Once the perimeters are established the areas within these structures can be measured and an overall percent voiding can be calculated. This type of measurement works well if the voids are large or found on the outer edges of the sphere but if the void is small and centrally located where the sphere density is the greatest then the void may be invisible due to its relatively similar gray level to the surrounding material. Increasing the X-ray power will reveal the small void but also shrink the measured area of the sphere and yield an inaccurate and inflated percent voiding. This problem is even more complicated in a chip or a leaded component solder joint. When X-raying a completed assembly, internal traces, vias and even components on the backside of the board that intersect the image of the solder joint confound the software algorithms ability to accurately determine the perimeter of the solder joint. In simple terms the X-ray image is two-dimensional and the ideal structure must be symmetrical about the Z-axis such as a box or a cylinder.

Novel Approach

Based on the assumption that the ideal quantitative void measurement method will utilize BGA analysis software and a symmetrical Z-axis reflow structure, the “sandwich” concept was developed.

This a novel approach simulates the worst conditions of a solder joint for voiding, under the component where flux evacuation is the most difficult while maintaining the same reflow thermal environment and metallurgies if desired. This idea was born out of a quest for a quantitative method of determining the percent voiding on a Ceramic Column Grid Array (CCGA)1. In the CCGA the columns are 10/90 Sn/Pb and cover about 45% of the solder fillet. If enough power is used to see through these dense columns, the perimeter of the solder joint is washed out and 55% of the total fillet is invisible. If adequate power is used to see the perimeter of the circular fillet, the area under the columns is invisible. The effort is complicated by column parallax, internal traces and vias as can be seen in Figure 1. With the thought of a column the same diameter as the solder pad that is thin enough to be X-rayed without excessive power, a solder preform was selected. In this application the preform alloy was selected to be the same as the 10/90 columns to minimize the variables that could contribute to solder voiding. Several thicknesses were tested with a 30 mil diameter by 5 mil thick as the final solution.

There were numerous challenges placing these discs. The first problem was a reliable source cup shaped and stacked discs were the first problems to solve. The second problem was the mechanics of actually placing the discs in that the vision systems in the pick and place were never programmed to recognize round components, only components with corners like typical chips. This relegated a “ballistic” pick and place strategy. For this problem a precision matrix tray with cylindrical pockets, each holding one preform, was developed as in Figure 2. Next came improvements to the pick and place nozzle. The stock smallest nozzle OD was the same as the preform. This presented numerous pick problems if the preform was not perfectly centered, occasionally the preform would flip on its edge after pick and crash on placement deforming the preform. Several improvements were made ultimately reducing the nozzle tip down to what would be typical for a 0201 chip as in Figure 3. Reducing the nozzle tip surface area helped eject the preform better in the placement operation.

Assembly of the CCGA test coupons is simple SMT assembly beginning with a “pads only” ceramic coupon to maintain the geometries and pad metalization of the application. This coupon is free of internal traces as in Figure 4. The solder paste is printed through a circular aperture that is 1 mil smaller in diameter than the pad, the preform is placed over the solder paste and then reflowed as in Figure 5. It was established that if the preform was off pad less than 4 mils that it would self-center. Careful attention to Z-axis placement is required to prevent shorting with adjacent preforms.

After assembly the coupon area was X-rayed and quantitative void analysis was performed on the image using off- the-shelf BGA analysis software as in Figure 6. This software provides both total percent voiding and a pass/fail status if any individual void within a structure is larger than a preset number (ie 5%). This technique worked very well for the custom formulated 63/37 Sn/Pb based solder paste or any other alloy with a similar melt point but when tested with lead free (Sn/Ag/Cu, Mp 219°C) it was noticed that the preforms had appeared to melt and partially join the underlying solder paste under test. This was remedied by switching to OFHC copper preforms of identical geometries. For generic paste void benchmarking2 a dedicated pad test area (Figure 7) was included in the Benchmarker II test board. This allows the testing of solder pastes on standard PCB surfaces such as Entek OSP (Organic Solder Protectant) and ENIG (Electroless Nickel Immersion Gold). Quite simply we are making copper sandwiches (Figure 8) that result in cylindrical structures, which permit highly quantitative void analysis with standard BGA analysis software.

rom this data there are clearly different trends for the two materials as well as a significant difference in void behavior between them. The effect of time on Material A is accelerated in cold storage and just the opposite with Material B. Both materials have the exact same source and specifications of the inorganics (powder + additives).

Profile Effects
The effect of the reflow profile can be significant but the magnitude varies greatly from one formulation to another. The following example involves two 63/37 Sn/Pb no clean materials3,4, tested over Entek passivated copper using the copper preforms with the 4 profiles as illustrated in Figure 10. This profile matrix is designed to expose profile sensitivity of a given formulation, in this case relating to voiding. There are two profiles with a ramp style preheat and two with a soak preheat. There are 2 profiles with a peak of 225°C with 60 seconds over liquidous and two hotter profiles with a peak of 240°C with an extended liquidous of 90 seconds. The X-ray data has been compressed into a single “point scale” to facilitate comparisons. These points (100 is best) are calculated .

How Does 3D AOI Increase Manufacturing Quality?

PCB suppliers in the automotive space are vastly accelerating their time to market by using automated optical inspection AOI systems during PCB assembly. However, this next‐generation technique is not limited in scope to the automotive industry – it has powerful implications for the entire PCB industry.

What is 3D AOI?
To best understand the benefits that 3D AOI offers, it's useful to compare it to its predecessor, 2D AOI. In the past, automated optical inspection processes allowed electronics manufacturers to identify workmanship defects and other issues during the final stages of PCB assembly.

In a typical AOI setting, a top‐mounted camera takes precisely measured photographs of finished circuit boards and compares the results to a highly detailed schematic file. Parameter differences that pass a certain threshold get flagged, and a human operator inspects the product in question.

The upshot of this process is that human operators no longer need to manually verify every parameter of a finished circuit board – for modern PCBs, that would take far too long. Now, a small team of operators can verify a very large volume of PCBs and pick out the defective ones with great accuracy.

3D AOI builds on this premise by using two cameras to develop a three‐dimensional image of the PCB. This allows the AOI process to verify smaller components than ever before. In some cases, the addition of a side‐mounted stereo camera set lets the optical image technology build a complete render of the PCB, allowing for unprecedented precision and quality control.

Who Uses 3D AOI for PCB Inspection?
As of mid‐2017, this technology is almost exclusively used in the autonomous vehicles industry. The ability to quickly identify and measure panel defects when dealing with extremely small components is an important factor contributing towards making autonomous vehicles an everyday reality.

However, as time goes on, this inspection process will become more commonplace, vastly reducing the time and energy spent on PCB inspection. Manufacturers are continually looking for better, more efficient test methods that offer real‐time feedback. This way, PCB defects can be identified early in the manufacturing process, saving customer grief and company reputation by preventing potential recalls or, in some industry sectors, lawsuits.

When combined with laser direct imaging (DI) technology, AOI improves yield by minimizing expensive material waste. The combination increases the traceability of the supply chain and helps manufacturers identify the factors that generate production failures.

The PCB Used In Marine Industry Paving Way For Innovations

The PCB Used In Marine Industry Paving Way For Innovations

As the technology has become a universal key to major developments, the marine and boat industry has shown elevated growth in recent time. The marine market circumscribes on the electronic and design solutions for every single innovation. All the developments in Marine sector has and are heading towards a notion of modernization and among these, printed circuit board is grounding the research and developments. How to increase the efficiency of the device? How to gain optimum fuel efficiency? Does the dual fuel concept become a buzz word for major innovations? These are the basic questions which are considered to bring new novelties in the market. This article is a detailed conspectus of marine and boat industry and the role of printed circuit boards in manufacturing modified marine electronic instrumentation. This will also drive you to the spotlights into the use of PCB prototypes, PCB assembly and PCB Design in Maritime industry, the commendable marine innovations/ New concepts and the prime factors affecting the modernization in the marine industry.

Awash with modernization, the marine market shows innovations in safety devices, telematics, equipments with resistance to vibration, underwater marine machinery and many more. The marine and boating industry shows a major concern for the protection of electrical resources from destruction due to climatic reactions and global warming. With this, the Submarines, weather sensors, marine gauges, underwater equipment, crane, flood detector, galvanic Isolator, fuel efficient motors and other tough marine applications need proven design to engineer the marine vessel manufacturing.

The electric connectivity and mechanical support provided by marine PCB’s is at the base to create an all to gather efficient Marine machinery and aquatic vessel. From manufacturing ship, yachts, craft and other aquatic vessels depend on printed circuit boards to control the marine mechanism with electronic process. Among all, Rigid/Flex PCB is majorly used in providing electronic solutions that have an efficient RF Module. The maritime electronic PCB are of many types depending upon the purpose of use. The double layered and multi layered PCB is used for complex compositions of marine vessels. Also high grade PCB material is used in the circuit board that well suits the climatic reactions in the sea. The PCB is at the base of every single marine innovation happening across the globe. To explore more insights into the PCB used in the Marine industry, it is equally important to know about the current Maritime industry.

Initially the marine market marked stagnation before few decades. Gradually, with a drift in technology, the boat and marine industry has picked up a pace with new developments. This can be marked in marine civil construction and engineering, underwater ad diving technology, marine equipment, marine electronics, renewable energy and marine security. The research for developments in maritime sector has added crowns in the small devices and large equipment as well. Few developments seen in small marine devices are outlined as under:


Marine load testing is an electronic portable equipment with strong hydraulic cylinder and customized ropes to create more than 120 tonnes of pull underwater. The underwater Impact torque device is a marine electronic tool to strongly tighten the screw and nuts to perfect torque. The saltwater pressure washer that works with the help of Diesel and is extensively used for maintenance and cleaning of wind farms. The design and structure of the machine is such that has resistance to the marine conditions and can efficiently wash the offshore wind farm. The radio combiner and other marine telecommunication devices have an ergonomic design for compact high speed craft.

Apart from these, boat/ship dashboards, exit lights, marine spotlights, navigation system, electronic counter measurement device, engine management, radar system, beacon and strobe system have markedbreakthrough modifications to make it a fuel efficient and time savvy marine operations.

Recent Concepts:
0The Advance Outfitting is the time and cost saver technique to manufacture the ship and heavy marine machineries. In this method, the ship building process involves assembling the marine outfits like seating, piping, machinery in a small unit which is fixed at its actual position afterwards in the hull block. This saves much time and cost as before the ship building process the hull is fabricated first and after launching the hull from the berth, the outfitting process starts that proves to be tedious and time consuming.

The Green Ship Technology to reduce the carbon is a step ahead to environmental protection. It has a solar cell integration with effective anti ballast system. For making marine operations greener, many other marine electronic devices are launched in the market that includes the optimized cooling system, engines to bring down the level of nitrogen oxide level, exhaust scrubber, solar cell hybrid system, dual fuel motors and many more.

Be it a new or an old concept driving the marine operations, few factors affect the modernization in Marine innovations. Among which the Environment is a top most factor of prime consideration. Another aspect that brings a Dinger in the maritime industry is making a move towards Digitalization of all the marine operations. At the end, researchers are now striving to trigger the innovations in electronic instruments and control system that has high applicability in the Marine industry. Among which the different types of PCB prototypes and PCB assembly services are grounding the studies to come up with better and better solutions for marine machine manufacturing.

More details of SMT Technology,pls refer to : Joy Technology Co., Limited