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