With fast paced technological advancements of the 21st century, the demand for electronics today is higher than ever. The supply now needs to meet the demand without failing to deliver quality. This is why older ways of outsourcing different production materials from various sources is no longer valid in today’s times, as sub contractors are unable to coordinate accordingly, which leads to flailing services and poor customer satisfaction rates.

This is why; it just makes sense to keep all the business under one roof.

Opting for an all-in-one-source contract electronic assembly firm will result in better assembled products that are delivered on time and in a cost effective manner. PC board is amongst the most essential components in any electronic device, so it is wise to ensure that your firm is getting duly assembled PC boards at competitive prices. Here are some ways in which an all in one contract is better than the other options available.

If the manufacturing firm that you have hired makes use of innovative Surface Mount Technologies, then rest assured it will give way to vast improvements in your board design, offeringnoteworthy cost-cuttingoptions. SMT-based parts are much smaller than their alternatives.They’re alsoless expensive. So you can create and assemble a fully functioning device with almost half the cost with SMT based parts. Furthermore, SMT designs allow you to exploit either side of a circuit board as well.

Part production and manufacturing firms that have been in the business for a long timepossess a wide gamut of component manufacturers to make the choice easier for you. More often than not, minor differences in component sources and trivial changes to the build can result in significantly diminished costs per-unit, with little or no decline in net product quality. Therefore, it is wise to search for alternative component sourcing options when you are entering the phase of device assembly.

If your contract electronic assembly service enables you to view prototypes more quickly and at lower costs as compared to employing a third-party for prototyping, it means that you are saving big on this aspect. It can also create extra feedback loops, fine tuned designs, and a guaranteed final build, based on the pre-selected prototype. This gives you flexibility in design and operation, and you are able to control wider facets of your device assembly.

Are you looking for an all-In-One Contract Electronic Assembly in China? If yes, then Asia Pacific Circuits is a one-stop shop where you can get all your PCB assembling needs addressed. From quick turn PCB assembly to other related services, we do it all. Get an instant quote by clickinghere and experience the best PCB services in China by reducing your budget costs.

Via-In-Pad (VIP) is rapidly becoming more commonly used in modern printed circuit design due to many considerations, including the need to miniaturize the PCB form factor. This review of via-in-pad technology can help remove some of the mystery of VIP in PCB manufacturing.

Via-In-Pad Structure Types

Pad diameter is the major factor in the device footprint that will determine what type of VIP structure is utilized; drilled-and-filled or laser microvia. In order to meet the minimum annular ring requirement of IPCClass 2 or Class 3 there must be sufficient pad size to accommodate the via diameter and allow for manufacturing tolerances.

Mechanically Drilled/ Epoxy Filled Vias

The available range of finished hole sizes for epoxy filled vias (mechanically drilled) is a minimum 0.008″ through a maximum of 0.018″. To consider the minimum finished hole size (FHS) of 0.008″ you must consider the pilot drill diameter (drill size before plating). A pilot drill diameter for 0.008″ FHS will be 0.010″, which will now determine the minimum pad size as defined by minimum annular ring.

Laser Drilled Microvias

Microvias require as little as 0.002″ annular ring (laser via diameter + 0.004″). Laser microvias have the advantage of not only being smaller in diameter than mechanical drills (0.003″ to 0.006″ typical diameter for PCB designs), but they have the ability to register much better as the process assures alignment to the sub-layer and the overall hole pattern will scale to match the sub-layer image in X and Y dimensions.

BGA Requirements

With BGAs, footprints with 0.5mm and less require microvias as the pad diameter is not large enough to accommodate mechanical drills. Microvias most commonly span a single dielectric thickness–ideally one half deep as the diameter (0.5:1 aspect ratio) with an a maximum depth equal to the diameter (1:1 aspect ratio). This is due to the fact that the fully copper plating process takes a substantial amount of time and is not designed to fill deep, blind holes that extend down deep into the board.

Do you have questions about VIP? Learn more here in our full discussion of the topic. You may also wish to discover more about this and Advanced Circuits’ full range of PCB manufacturing and assembly capabilities. For over 25 years, Advanced Circuits has provided its customers in the high tech aerospace, military (DOD contracts ready), medical, and commercial industries with printed circuit boards that deliver powerful performance, reliability, and precision for critical applications. Advanced Circuits’ over 10,000 customers rely on the highest quality standards they receive for all PCBs, from simple prototypes to complex designs requiring microvias and machining.

The Software Lifecycle Landscape
With the development of embedded hardware, careful attention is given to the design and creation of highly detailed specifications that can be used to source board components. This is usually followed by a phased delivery set of milestones including: prototype, implementation, test supplier qualification and final release to production. This regimen offers the advantage of ensuring quality and functional requirements being met by the time manufacturing. Taking a waterfall approach to hardware development can minimize any risk of downstream issues once hardware goes into volume production.

Software development is perceived to be completely different. The “soft” part in software implies there is an inherent ability to change along the way. Unfortunately, this can give management a false impression that software projects can easily accommodate change with little to no additional cost or schedule impact. The perception of a software developer is further glamourized in Dilbert cartoons by Scott Adams. [1] A programmer is considered to be a breed apart—working in a world combining art, technical inquisitiveness, social discomfort and sometimes even magic. All you need is creative talent, endless hours, lots of coffee, a PC and a handful of software tools.

As hardware development projects are perceived to complete on a timely basis, software development projects are often late and cost much more than was originally planned. Just ask any project manager in the embedded industry who has worked on both hardware and software projects. Given the choice, many project managers would rather manage hardware projects.

Since both software and hardware projects may be under development at the same time, both sets of teams must collaborate. As hardware developers tend to work in a very structured and organized manner, software engineers tend to perform a lot more trial and error. This “software way of life” can be quite a challenge for management and I’ve seen more than one attempt in my career to convert more-disciplined hardware engineers to become programmers. This rarely works due to different skill sets and a radically different mindset.

Rather than demand that software people conform to hardware design approaches, a better way is to take lessons from enterprise and mobile software computing. We must identify the right approach for software development that marries the way software developers like to work with how work is performed.

Audit Your Software Development Lifecycle
Years back, my Datalight software development team was having a tough time juggling incoming product management requests making project schedules difficult to achieve. At the time, any mention of changing our process methodology to agile (specifically, Scrum) was met with, “no way! That stuff is just a fad.”

I found it was easier to let the team identify what didn’t work at the time rather than force fit some newfangled agile methodology on them. So, I asked the team, “OK, what can we improve with our software development process?” Through rather intense brainstorming, we were able to compile a list of improvements to be made:

• Users aren’t always sure what they want and once they see the work, they want it changed.
• Details usually come out during implementation so committing to upfront schedules is not possible.
• Approved specs are rarely accurate by the time a project is completed.
• Disconnected long series of steps with handoffs are typically subjective.
• Success seems far, far away and, in practice, schedules aren’t very predictable. This results in the team not seeing any work completion for possibly months. And then the problem begins when QA gets their hands on the code.

A unique characteristic of Scrumming software development projects is that a product owner and the customer should be represented at Scrum planning, sprint planning and sprint reviews. During a sprint review, also called a sprint retrospective, the customer has the opportunity to review progress and the team can adjust to that feedback in the next sprint.

 by Bruno Tolla, Ph.D., Denis Jean and Xiang Wei, Ph.D.

Several performance attributes must be considered under challenging thermal conditions.

The design of fluxes for a selective soldering application poses unique problems due to the localization of the soldering process. Both the heat treatment and the scrubbing action of the flux residue by the solder wave are confined in the soldered area. To address this specific issue, the flux formulator follows two complementary strategies.

First, the physical characteristics of the flux are optimized in synergy with the application process to minimize its footprint on the board. The flux must work in concert with the drop jet dispensing head to flow seamlessly (e.g., no clogging) during the entire operation, localize the deposit and, finally, stay in place.
Dispensing process parameters (open time, frequency, robot speed), as well as the board preheat temperature, are critical parameters,1 and their optimal settings depend on the characteristics of the flux (viscosity, surface tension, solid content, solvent).

Assembly materials also play an important part, as the optimal surface energy of the solder mask is typically lower than that for the conventional wave soldering process (35mN/m vs >50mN/m) in order to prevent excessive bleeding of the flux on the board after deposition. Hence, the design of a selective soldering flux is a good illustration of the mandatory collaboration between the formulators, equipment and assembly materials manufacturers from the very beginning of the design process.

Second, the flux chemical package is formulated to minimize the impact of unavoidable spreading and splashing events. These will result in partially heated flux residues, which won’t be removed by the washing action of the solder. As such, they pose a serious threat to assembly reliability, as ionic residues can induce electrochemical migration, corrosion and resistance losses, which could result in the in-field failure of the assembly when exposed to a moist environment.2,3 It is therefore of paramount importance to establish a correlation of the thermal history of the flux with the reliability of the residues. From this perspective, a series of activator packages has been designed specifically to guarantee an optimal reliability when partially heated.4 The reliability of the fluxes designed for the selective soldering application was assessed using common industry standards, where the flux was subjected to various thermal conditioning (TABLE 1).

TABLE 1. Flux Reliability Testing Methods


A statistically significant experimental protocol was conducted on Ersa selective soldering equipment to evaluate the impact of materials and process parameters on the following response factors: dispensing performance (clogging and satellites), flux spread and soldering performance. The results of these experiments are reported in the following paragraphs.

Flux spread. Flux spread is influenced by the surface tension of the flux and its temperature.  Alcohol-based fluxes have a much lower surface tension than VOC-free fluxes, which are water-based (22mN/m at 25˚C vs. 72mN/m). Also, the dispensing temperature will tend to favor spreading by lowering the flux viscosity.

On the other hand, the impact of the board preheat will depend on the nature of the flux; VOC-free fluxes tend to spread more on warmer boards, while an alcohol-based board will show an opposite trend as the temperature thinning effect competes with the high drying rate of the flux. Finally, the surface energy of the solder mask is another critical parameter; lower surface energies are favored for selective soldering fluxes compared with conventional wave soldering fluxes (35mN/m vs > 50mN/m) to increase the contact angle of the flux on the substrate. This is easily understood when looking at the balance of surface
tensions modeled in Young’s equation: γSG=γSL+γLGcosθ. It should be noted preheating the board may impact the surface energy of the solder mask.

We estimate the intrinsic spreading of fluxes by deposition on a representative set of PCBs with various solder mask types. In contrast, in-process optimizations of the flux spread are conducted by directing the drop jet on the shiny side of an aluminum foil, which presents a comparable surface energy, and measuring the dried deposits after preheat as illustrated in FIGURE 1.

FIGURE 1. Flux spread measurement (Left: PCB; right: Al foil).

Drop jet dispense: clogging and satellites. High-frequency drop jet technology has been developed to narrow the spray pattern compared to atomizing-type aerosol spray heads or ultrasonic spray fluxers. The deflection of the flux droplets is minimized, but occurrence of satellites is always a possibility; these very small flux droplets varying in sizes appear in random directions outside of the flux direct deposition corona. They depend on the flux physicochemical characteristics (viscoelastic properties, surface tension), hence its formulation, coupled with the jetting process itself. It is critical to mitigate the formation of satellites, as these side deposits won’t be exposed to the same heat cycle and solder scrubbing mechanism as non-deflected droplets, and will therefore pose a serious threat of electrochemical migration under bias in a moist environment.

Another processing issue frequently encountered during dispense is the clogging of the drop-jet fluxer, as a result of the narrow channels of the spray head (typically 130µm) combined with the high-volatility of alcohol-based selective soldering fluxes.

Both clogging and satellite formation are assessed during the same set of experiments, which enable us to screen our flux formulation efficiently on industrial selective soldering equipment. Fax paper is used to identify the location of the geometry of droplet deposits. It should be noted that use of fax paper for in-process spread measurement is typically avoided, as the absorption of flux into the fabric of the substrate will result in an inaccurate representation of the flux spread data.

The tests consist of successive deposition cycles executed at increasing time intervals. Twenty dots are printed at 2 sec. intervals in one cycle. This sequence is repeated four times, with 30 sec. breaks between each cycle. The whole procedure is then repeated four times, this time with 15 min. breaks in between. The dot geometries and satellite positions are computed for the 500 dots deposited in total using image analysis software. The successive breaks during the sequence make the procedure particularly aggressive. In our experience, a continuous flow of flux through the drop jet unit self-regenerates the head, while the breaks give time for the deposits to accumulate, ripen and create solid deposits on the side, which are more difficult to remove when the sequence is restarted. In consequence, fluxes can be efficiently discriminated through this experimental protocol.

FIGURE 2 shows a representative set of deposition patterns obtained with various fluxes: the flux #2 deposition conditions were near perfect, while #10, #6 and #13 show multiple defects. Observe that satellites and variations in surface area of the deposit often happen at the beginning of the sequence, where
deposit concentration is at its maximum, which demonstrates this effect is the major root cause for dispensing failures.

FIGURE 2. Typical deposition patterns for the drop jet dispensing test.

Overall, 15 formulas were screened using the statistically significant set of data generated during these complex  deposition sequences. Results of the deposition pattern analysis are reported in FIGURE 3. The efficiency of this screening method is confirmed, as large differences are observed between fluxes, in terms of uniformity of the deposits across the whole deposition sequence (dot area and dot circle), as well as the occurrence and spatial distribution of the satellites. Fluxes #1, 2, 3 and 4 present the best dispensing performance and were selected for the final soldering performance assessment.

FIGURE 3. Dispensing test results for 15 experimental formula. Statistical analysis of 500 data points per formula, collected through an image analysis software.

Soldering performance. A performance evaluation was completed on an industrial selective wave soldering machine from Ersa (FIGURE 4), using 93 mil FR-4 boards made of four copper layers (1/2/2/1 oz.), solder mask over bare copper (SMOBC) and an OSP finish (FIGURE 5).

FIGURE 4. Selective soldering equipment configuration.

FIGURE 5. Selective soldering testing board.

These boards were populated with 16-pin dual inline packages (DIPs) containing IC chips and 96-pin Eurocard connectors.

To determine the soldering performances of the fluxes, the L16 Taguchi design of experiment reported in TABLE 2 was used.  

TABLE 2. Soldering Performance DoE parameters


The response factors were flux spread (measured area), % hole fill (evaluated by x-ray diffraction), and the number of solder bridges and solder balls (visual count).
The statistical analysis of the results is reported in FIGURE 6. Main effects are represented here, as second-order interactions were found to be statistically insignificant.

FIGURE 6. Soldering performance DoE results.

All fluxes presented similar spreading results, the only impactful process parameter being the dispensed volume. Hole fill performance was found to be comparable between fluxes, while particular attention needs to be given to the board preheat temperature. This result is in good agreement with our background knowledge.  Preheat times are relatively long in point-to-point selective soldering applications, which poses a challenge to the thermal stability of the activator packages. In this context, very satisfactory performance is found with all fluxes for a preheat temperature of 110˚C. More flux discrimination was found when considering soldering defects. Flux #1 clearly stands out compared with the three other fluxes, with minimal defect rates observed in all conditions. The strong impact of board preheat temperature on defects confirms our initial interpretation on the activators’ thermal stability envelope.

Conclusion
The design of high-performance fluxes for selective soldering applications requires a combination of formulation, application and equipment expertise that mandates a strong partnership between flux designer and equipment manufacturer. Multiple performance aspects have to be taken into account. The flux itself must have proven reliability (corrosion, electrochemical migration) under various heat exposure conditions, in particular when only partially activated. Having down-selected a series of fluxes filling this requirement, it is necessary to conduct statistically designed experiments on industrial wave soldering machines to map the relationships between flux characteristics and selective process friendliness. In this area, multiple performance attributes are considered: compatibility with drop jet dispensing (clogging effects, cleaning frequency, and satellite formation), spreading on the board (in actual processing conditions, with multiple solder resist types) and soldering performance (fluxing activity, thermal stability) as measured by barrel filling and defect production.

MEMS gyroscopes offer a simple way to measure angular rate of rotation, in packages that easily attach to printed circuit boards, so they are a popular choice to serve as the feedback sensing element in many different types of motion control systems. In this type of function, noise in the angular rate signals (MEMS gyroscope output) can have a direct influence over critical system behaviors, such as platform stability and is often the defining factor in the level of precision that a MEMS gyroscope can support.

Therefore, “low-noise” is a natural, guiding value for system architects and developers as they define and develop new motion control systems.  Taking that value (low-noise) a step further, translating critical system-level criteria, such as pointing accuracy, into noise metrics that are commonly available in MEMS gyroscope datasheets, is a very important part of early conceptual and architectural work.  Understanding the system’s dependence on gyroscope noise behaviors has a number of rewards, such as being able to establish relevant requirements for the feedback sensing element or, conversely, analyzing the system-level response to noise in a particular gyroscope. 

Once system designers have a good understanding of this relationship, they can focus on mastering the two key areas of influence that they have over the noise behaviors in their angular rate feedback loops: (1) developing the most appropriate criteria for MEMS gyroscope selection and (2) preserving the available noise performance throughout the sensor’s integration process. 

Motion control basics

Developing a useful relationship between the noise behaviors in a MEMS gyroscope and how it impacts key system behaviors often starts with a basic understanding of how the system works.  Figure 1 offers an example architecture for a motion control system, which breaks the key system elements down into functional blocks. The functional objective for this type of system is to create a stable platform for personnel or equipment that can be sensitive to inertial motion.  One example application is for a microwave antenna on an autonomous vehicle platform, which is maneuvering through rough conditions at a speed that causes abrupt changes in vehicle orientation.  Without some real-time control of the pointing angle, these highly-directional antennas may not be able to support continuous communication, while experiencing this type of inertial motion. 

Figure 1: Example Motion Control System Architecture

The system in Figure 1 uses a servo motor, which will rotate in a manner that is equal and opposite of the rotation that the rest of the system will experience.  The feedback loop starts with a MEMS gyroscope, which observes the rate of rotation (ω_G) on the “stabilized platform.”  The gyroscope’s angular rate signals then feed into application-specific digital signal processing that includes filtering, calibration, alignment and integration to produce real-time, orientation feedback, (φ_E). The servo motor’s control signal (φ_COR) comes from a comparison of this feedback signal, with the “commanded” orientation (φ_CMD), which may come from a central mission control system or simply represent the orientation that supports ideal operation of the equipment on the platform.