Manufacturing Engineering builds Design Notes

• Snubbers consisting of R-C should be used across switches, relay contacts, MOSFETS when switching inductive loads, this will absorb the spike and save the device.
• Use RTV (room temperature vulcanizing) silicone rubber compound or Varnish on PCB-devices to avoid corrosion-dust. more so in industrial environment, ships and chemical industries.
• Transformers used in SMPS could be split bobbin for product safety, and transformers should be resin impregnated, a human life cannot be lost by using a badly made product.
• Ceramic capacitors leak a bit, electrolytics leak a lot but plastic or mica capacitors do not leak at all, near perfect. An oscillator with a RC time setting needs a plastic cap for stability.
• 12V lead acid batteries should be charged with a constant current CC and constant voltage charger the CV being 13.6V. Deep discharge and over charging will reduce the cycles.
• Lead acid batteries need a monthly distilled water update to ensure long life, sealed lead acid dont need attention. Keep lead acid batteries in well ventilated area due to acid fumes.
• In a SMPS which is not earthed the floating (unconnected) earth terminal will give a slight shock due to the two Y caps connected to earth from phase and neutral.
• Electric Shock can kill hence take great care, Electrolytic capacitors burst and Transformers catch fire. turn off equipment after use. turn off all electricity when going out of town.
• In industrial electronics equipment, connectors are a source of many problems, hence avoid connectors. vibrations, corrosion and frequent usage will result in strange problems.
• A DMM in diode mode or resistance mode can be used to test IR diodes, take it under 100W lamp and measure, cover the IR diode and measure you will see a response in proper polarity.
• Alumina-Aluminum oxide powder mixed in epoxy resin (araldite) can make thermally conductive insulating filler, heatsinks. The Alumina must be free of moisture and very dry.
• Inductive kickback starts a tubelight or automobile as high voltages are produced when current in inductor is turned off. This also is the cause of failure in power semiconductors.

Protect your Design

Hardware protection : If you have made an electronic product with a new circuit and need to protect it then these are the ways that i used.

1. Security Bit -
Use for digital logic area, an atmel uC with security bit protection or any uC-uP with internal memory read protected with security bit. the firmware should be kept in tight control from both external people and your employees and must be on a non-networked and non-internet machine.

2. Hermetically seal -
This is a crude and ancient way, delete the chip part numbers and pot it in a plastic can with ciba araldite epoxy with alumina filler, this way product may not be copied and it will be immune to vibration and corrosive environment. but heat dissipation and serviceability is affected, so make a epoxy potted module of only some part of the circuit.

3. Make ASIC or FPGA -
ASIC is only for volume production and is copy protected, if you design inhouse and the chip maker you order is trustworthy, then this is ok, for small volume production use FPGA, CPLD, DSP uC or uP with read protection as practical.

4. Go open source -
Design a circuit and put it on the internet to share, let the community use it and improve it, here also revenue is made by service of product, custom design and customer support and this will work long term free of tensions. This way has proved to foster greater innovation and stable technologies.

(my dairy log 2002, Amps-n-Volts June 2005, Now logged here - delabs)

Product Design Precautions

Black Box Specifications

• Start Projekt {
  
• Customer Interaction and Communication to make a specs sheet and drawing.
• Block Diagram, feasibility, cost, risk, samples demo and study similar ideas.
• Effective designs are cost effective within customer budget, draft BOM costing.
• Circuit and Code design and get more inputs from customer and then freeze specs.
• Build Dummy for ergonomics and discuss, Prototype and start test at site or simulate.
• Calibration and testing and production documentation drafts final costs.
• Pilot Production of a small batch, rigorous test batch, and freeze production documents.
• Documents and Prototypes to be given to Production Engineering.
• Production Engineering continue engineering maintenance and quality issues.
  
• } End Projekt
  
  GoTo Next Projekt

(I had written this in Aug-05, it is my experience, it may indicate some useful points - delabs)

Product Design and Manufacturing Knowledge

• On-Off controls or level trip relays can oscillate if hysteresis dead band is very small or absent.
• Use silicone shrink sleeves to insulate or close exposed high voltage wire ends or joints.
• When you make your prototype check diode and el-cap polarity, check pin 1 of chips and connectors, resistor values, dry solder and loose contacts, hairline cuts or shorts, e-b-c etc. of Transistors, FETs and thyristors.
• Just like in ICs, product design is of three types commercial, industrial and military or medical.
• LED displays are best indoors and are not so good for sunlit outdoors, LCD is good for that.
• Test a mosfet, charge the gate with the DMM in diode mode, then there is a short between source and drain.
• Sharp bends in PCB tracks or wires will radiate away the RF energy, so do not have hairpin bends.
• Make a 3D mockup of the final product, both the box and the PCB with components before PCB done.
• Theory and simulation can give you only 50% of the picture, you have to breadboard to test properly.
• The products that survive the infant mortality time of say first six months will last quite long.

Soldering an Desoldering Tips

When you are desoldering a double sided pcb, use a desoldering pump or desoldering wick. Heat a joint to be desoldered and then quickly tap it hard on the table, the molten lead will fall off.

Use the soldering iron as a heat transfer tool, heat the junction of the lead of the component and the copper pad on pcb then touch the hot junction with a flux cored soldering lead wire, it should melt and form a concave shining joint. If air bubbles are formed or you see dull convex joints, then it means you have a dry solder and bad contact. Leads of old components due to exposure to moisture, brine or sunshine will corrode, store them well cool-dry-clean-air. Anyway scratch them with a blade and solder them with extra flux.

PCB Thermal Design Care for Analog Circuit Stability

If you have a hot power chip near a DC analog circuit, the values will drift, take time to stabilize, this happens even if you use 1% MFR 100ppm. The impact is more if the heatsink is not used and vents and coolers are absent, So in a PCB keep distance between heating power circuits and sensitive analog circuits, some times PCB tracks will carry heat to the Analog area, Hence keep sensitive analog circuits as plugin modules.

Related Reading -

• MOSFET testing
• Testing a MosFet, Testing
• RF PCB design - a compromise for product performance and yield