Production Notes – Prototype Fabrication – 03

Prototype Fabrication

Sometimes a component can be defective, may not be what it is labeled or may be of a wrong value. In manufacturing 100% incoming inspection of components can catch these errors, Before Assembly of prototypes just test all passive and active components with a DMM and put all ICs in bases, then troubleshooting is easy.

  • 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.
  • Observe color code in wires. positive is red and negative is black and green is earth and See Wire Color Code.
  • When you are soldering or cutting leads, room should have cross ventilation, protective glasses for eyes and a good stand.
  • When using a sharp blade the cutting stroke must move away from you and make sure nobody is close, Wear protective or even plain glasses, If you use a blade with the stroke moving towards your body it will cut badly.
  • Power tools and machinery must be used only after exhaustive training and with safety precautions. The power tools used carelessly and wrongly can cause an injury which will last a lifetime or may even handicap you.
  • Have a lathe lamp or table lamp with a 40W edison-filament lamp (ordinary bulb) on your workbench.
  • Have an antistatic mat on the work or test table, if you cannot afford or get it then get a large aluminum sheet, laminate it with an insulating polycarbonate sheet and earth the metal plate with two 1M resistors in series.
  • Use thin multi strand teflon wires for your jumpers within a PCB, these are not damaged by your iron too.
  • Silicone shrink sleeves can withstand high temperature and use this in your work to make it safer and neat.
  • When you make a connection with a wire you need mechanical strain relief or on use connection will open.

Soldering and Desoldering Tips

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.

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.

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