User:Ankitstech/sandbox

Process capability:

A process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output.Process capability is also defined as the capability of a process to meet its purpose as managed by an organization's management. Two parts of process capability are: 1) Measure the variability of the output of a process, and 2) Compare that variability with a proposed specification or product tolerance. If the process is not in statistical control then capability has no meaning. Engineers can conduct a process capability study to determine the extent to which the process can meet these expectations. The ability of a process to meet specifications can be expressed as a single number using a process capability index or it can be assessed using control charts Statistical process control defines techniques to properly differentiate between stable processes, processes that are drifting (experiencing a long-term change in the mean of the output), and processes that are growing more variable. Process capability indices are only meaningful for processes that are stable (in a state of statistical control).

Process capability index

statistical measure of process capability: the ability of a process to produce output within specification limits

SIX SIGMA

Six Sigma seeks to improve the quality of process outputs by identifying and removing the causes of defects (errors) and minimizing variability in manufacturing and business processes

A six sigma process is one in which 99.99966% of the products manufactured are statistically expected to be free of defects (3.4 defects per million). Quality management tools and methods used in Six SigmaWithin the individual phases of a DMAIC or DMADV project, Six Sigma utilizes many established quality-management tools that are also used outside Six Sigma. The following table shows an overview of the main methods used.

5 Whys Analysis of variance ANOVA Gauge R&R Axiomatic design Business Process Mapping Cause & effects diagram (also known as fishbone or Ishikawa diagram) Check sheet Chi-squared test of independence and fits Control chart Correlation Cost-benefit analysis CTQ tree Design of experiments Failure mode and effects analysis (FMEA) General linear model Histograms Pareto analysis Pareto chart Pick chart Process capability Quality Function Deployment (QFD) Quantitative marketing research through use of Enterprise Feedback Management (EFM) systems Regression analysis Rolled throughput yield Root cause analysis Run charts Scatter diagram SIPOC analysis (Suppliers, Inputs, Process, Outputs, Customers) Stratification Taguchi methods Taguchi Loss Function TRIZ Process Window Index (PWI)

is a statistical measure that quantifies the robustness of a manufacturing process which involves heating and cooling, known as a thermal process. In the electronics manufacturing industry, PWI values are used to calibrate the heating and cooling of soldering jobs (known as a thermal profile) while baked in a reflow oven. PWI measures how well a thermal process fits into a user-defined process limit known as the specification limit. The specification limit is the tolerance allowed for the process and is statistically determined. In the electronics industry, these specification limits are known as the process window, and values that a plotted inside or outside this window are known as the process window index

5 Whys

The key is to encourage the trouble-shooter to avoid assumptions and logic traps and instead trace the chain of causality in direct increments from the effect through any layers of abstraction to a root cause

ISHIKAWA

6 Ms (used in manufacturing industry)Machine (technology) Method (process) Material (Includes Raw Material, Consumables and Information.) Man Power (physical work)/Mind Power (brain work): Kaizens, Suggestions Measurement (Inspection) Milieu/Mother Nature (Environment

The 7 Ps (used in marketing industry) Product=Service Price Place Promotion People/personnel Process Physical Evidence [edit] The 5 Ss (used in service industry) Surroundings Suppliers Systems Skills

Statistical process control (SPC):

is a method of quality control which uses statistical methods. SPC is applied in order to monitor and control a process. Monitoring and controlling the process ensures that it operates at its full potential Safety SPC is a valuable process because it allows examination of specific parts of a process. In particular, it looks at the parts that may conceal sources of variation in the quality of the product An advantage of SPC over other methods of quality control, such as "inspection", is that it emphasizes early detection and prevention of problems, rather than the correction of problems after they have occurred

Reflow soldering

is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or several electrical components to their contact pads, after which the entire assembly is subjected to controlled heat, which melts the solder, permanently connecting the joint. Heating may be accomplished by passing the assembly through a reflow oven or under an infrared lamp or by soldering individual joints with a hot air pencil. Reflow soldering is the most common method of attaching surface mount components to a circuit board. The goal of the reflow process is to melt the solder and heat the adjoining surfaces, without overheating and damaging the electrical components. In the conventional reflow soldering process, there are usually four stages, called "zones", each having a distinct thermal profile: preheat, thermal soak (often shortened to just soak), reflow, and cooling  Preheat zone lengthiest of the zones and often establishes the ramp-ratefalling between 2.0 °C and 3.0 °C (4 °F to 5 °F) per second. If the rate exceeds the maximum slope, damage to components from thermal shock or cracking can occur. Solder paste can also have a spattering effect The preheat section is where the solvent in the paste begins to evaporate, and if the rise rate (or temperature level) is too low, evaporation of flux volatiles is incomplete

Thermal soak zone 60 to 120 second exposure for removal of solder paste volatiles and activation of the fluxes and remove the oxides, fluxes may not fully activate if the temperature is too low. At the end of the soak zone a thermal equilibrium of the entire assembly is desired just before the reflow zone  Reflow zone the part of the process where the maximum temperature is reached. An important consideration is peak temperature, which is the maximum allowable temperature of the entire process

THERMAL PROFIKLING

A PWI greater than or equal to 100% indicates that the profile does not process the product within specification. A PWI of 99% indicates that the profile processes the product within specification, but runs at the edge of the process window.[3] A lower PWI value indicates a more robust profile

Wave soldering

is a large-scale soldering process by which electronic components are soldered to a printed circuit board (PCB). the use of waves of molten solder. The process uses a tank to hold a quantity of molten solder; the components are inserted into or placed on the PCB and the loaded PCB is passed across a pumped wave or waterfall of solder. The solder wets the exposed metallic areas of the board (those not protected with solder mask, a protective coating that prevents the solder from bridging between connections

Used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued by the placement equipment onto the printed circuit board surface before being run through the molten solder wave.

solder machine consists of three zones: the preheating zone, the fluxing zone, and the soldering zone. An additional fourth zone, cleaning, is used depending on the type of flux applied A typical solder has the chemical makeup of 50% tin, 49.5% lead, and 0.5% antimony

Spray fluxer Foam fluxer

The preheating zone consists of convection heaters which blow hot air onto the PCB to increase its temperature Preheating is necessary to activate the flux, and to remove any flux carrier solvents. Preheating is also necessary to prevent thermal shock

Soldering This process is sometimes performed in an inert nitrogen (N2) atmosphere to increase the quality of the joints. The presence of N2 also reduces oxidization known as solder dross.

Effects of wave soldering[edit] DefectsCracks in the solder can occur and are usually caused by stress on the solder and can cause a loss of conductivity. Cavities, pores in the solder, can be caused by contaminated surfaces, insufficient flux, and insufficient preheating. Cavities can reduce strength and conductivity. Improper solder temperature or conveyor speed can cause an undesired thickness. If the solder is too thin, then it is susceptible to stress and may not support the required load. If it is too thick, then unwanted shorts and bridging can occur. Poor conduction in the solder can be caused by contaminated solder and can cause the product to be disfunctional.

[edit] Excess heatExcess heat can cause the circuit board to delaminate, become brittle, and become warped. Excess heat can also damage components that are sensitive to heat..

A failure modes and effects analysis (FMEA) used in product development, systems engineering, reliability engineering and operations management for analysis of failure modes within a system for its severity and likelihood of the failures.Identify potential failure modes based on past experience with similar products or processes or common failure mechanism logic, enabling the team to design those failures out of the system with the minimum of effort and resource expenditure, thereby reducing development time and costs. It serves as a form of design review to erase weakness out of the design or process. effects analysis refers to studying the consequences of those failures on different system levels.

Advantages Improve the quality, reliability and safety of a product/process Improve company image and competitiveness Increase user satisfaction Reduce system development time and cost Collect information to reduce future failures, capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact on company profit margin Improve production yield

Types of FMEA Process: analysis of manufacturing and assembly processes Design: analysis of products prior to production Concept: analysis of systems or subsystems in the early design concept stages Equipment: analysis of machinery and equipment design before purchase Service: analysis of service industry processes before they are released to impact the customer System: analysis of the global system functions Software: analysis of the software functions

First pass yield (FPY): also known as throughput yield (TPY), is defined as the number of units coming out of a process divided by the number of units going into that process over a specified period of time.[1] Only good units with no rework are counted as coming out of an individual process.

Example : 100 units enter process A, 5 were reworked, and 90 leave as good parts. The FPY for process A is (90-5)/100 = 85/100 = .8500

Also related, "first time yield" (FTY) is simply the number of good units produced divided by the number of total units going into the process. First time yield considers only what went into a process step and what went out, while FPY adds the consideration of rework.

Example : 100 units enter A and 90 leave as good parts. The FTY for process A is 90/100 = .9000

Conformal coating material is applied to electronic circuitry to act as protection against moisture, dust, chemicals, and temperature extremes that, if uncoated (non-protected), could result in damage or failure of the electronics to function

Applications:

Precision analog circuitry contaminated with ionic substances such as fingerprint residues,become weakly conductive in the presence of moisture.Reduce the effects of mechanical stress and vibrations on the circuit and its ability to cope in extreme temperatures.

For example, in a chip-on-board assembly process, a silicon die is mounted on the board with an adhesive or a soldering process, then electrically connected by wire bonding,encapsulated in a version of conformal coating called "glob top." This prevents accidental contact from damaging the wires or the chip.Increase the voltage rating of a dense circuit assembly; an insulating coating can withstand a much stronger electric field than air, particularly at high altitude.

coating is far more effective if all surface contamination is removed first, using process such as vapor degreasing or semi-aqueous washing in a special machine. Extreme cleanliness also greatly improves adhesion. Pinholes would defeat the purpose of the coating, because a continuous contaminant film would be able to make contact with the circuit nodes and form undesired conductive paths between them.  Coating methods: brushing (suitable for low volume application,many defects such as bubbles.The coating also tends to be thicker) spraying(spray aerosol or dedicated spray,suitable for low and medium volume processing the lack of penetration can be an issue where coating is desired to penetrate under devices.) dipping( highest volume technique.[3] Coating penetrates everywhere,THICKNESS IS ISSUE) by selectively coating via robot( involves needle & atomised spray applicator, non-atomised spray or ultrasonic valve technologies that can move above the circuit board and dispense / spray the coating material in selective areas. Flow rates and material viscosity are programmed, so that the desired coating thickness is maintained.[4] This method is highly effective at large volumes.limitations IS such as potential capillary effects around low profile connectors which "suck" up the coating accidentally.

Curing and Drying: Solvent & Water based conformal UV curing UV Conformal.

Thickness & Measurement\ Coating material when dry (after curing)have a thickness of 30–130 µm (0.0012–0.0051 in) when using acrylic resin, epoxy resin, or urethane resin. For silicone resin, the coating thickness recommended by the IPC standards is 50–210 µm (0.0020–0.0083 in).

Conformal Coating Selection": The most common[citation needed] standards for conformal coating are IPC A-610[10] and IPC-CC-830.[11] These standards list indications of good and bad coverage and describe various failure mechanisms such as dewetting[12] and orange peel.

Coating Chemistries:

Acrylic Epoxy Polyurethane Silicones Fluorinated or non Fluorinated - Poly-Para-Xylylene (Parylene) Amorphous Fluoropolymer

Material considerations: What is being protected against? (e.g., moisture, chemicals) What temperature range will the electrical device encounter? What are the physical, electrical, and chemical requirements for the coating material itself? Electrical, chemical, and mechanical compatibility with the parts and substances to be coated How easily can the material be reworked once applied?[16] How fast does the material dry (cure)?[17] How fast can the material be applied and dried (throughput time)?[17] What type of process and equipment is necessary to achieve the required coating quality (uniformity and repeatability)?[18] Price of the material per litre.[citation needed] Quality of the material supplier (two acrylic material manufacturers will not make equal quality of material).

Failures /Quality issues:

Improper choice of coating an acrylic coating would not be the ideal choice for an automotive application, because this coating type tends to soften with the high temperatures and exposure to moisture or petroleum residues. A better choice would be a silicone coating, which has a usable operating range of -55°C to +200°C and offers resistance to high humidity environments An ultraviolet (UV) cured coating may not be the best choice if the assembly has high-profile components. Shadowing can leave uncured coating which compromises the reliability of the PWB.

Shelf life and pot life

Moisture permeability

Thickness of coating

Out-gassing occur with heat, vacuum, or both, and results in a coating’s loss in weight from volatile emissions. Out-gassing can also occur as a by-product of the curing step. Silicone coatings using an acetoxy-cure can release acetic acid. This failure mode is usually a concern for the aerospace industry,

Uncured coating

De-wetting

Surface contaminants

Bubbles

Cracking

Orange ppeel