Soldering Basics

2 Overview  Introduction Definition Equipment  Procedure Preparation Execution Finishing  Specific Techniques Desoldering Tinning  Conclusion  References

3 Introduction – Definition  Unite two base metal items  Add filler metal (solder) Typ. < 842°F (450°C) melting point Metal flows via capillary action Metal bonds via wetting action  Metallurgical joint exhibits Fair mechanical strength Excellent electrical conductivity Watertightness

4 Introduction – Common Usage  Electronics  Plumbing  Stained glasswork  Jewelry  Orthodontics

5 Introduction – Equipment  Solder Joint filler metal Metallic alloy  Sn/Pb Typ. 60/40 or 63/37 mix 60/40 374°F (190°C) 60/40 364°F (183°C)  Pb-free EU RoHS compliance Typ. Sn/Ag/Cu alloy 422–433°F (217–223°C)

6 Introduction – Equipment  Flux Removes base, filler metal oxides Aids wetting process Rosin-based flux Availability  Separate paste  Flux-in-core solder Primary fume component…

7 Introduction – Equipment  Soldering Iron Solder melting heat source Power rating  Higher power ≠ higher tip temp  Higher power  heat larger joints  15-35W for electronic work Various tips available  Conical, chisel types  Tip width ~ 70-90% contact width Never use ‘cold heat’ irons on electronics!

8 Introduction – Equipment  Solder wick Braided copper strands Flux impregnated Absorbs solder when heated Remove excess solder Desolder components  Solder stand + sponge Always return iron when unused Always clean tip  Remove burnt flux  Remove excess solder

9 Introduction – Equipment  Heat sink Protect heat sensitive components Clip between component body and iron Substitution  alligator clips  Hemostat  99% alcohol + brush Clean joint residual flux Purity important

10 Procedure – Preparation  Clean components Remove dirt, grease, oxidation Causes unwettability Solder tend to bead up Component leads bright, shiny Solder pads bright copper color Fine steel wool, emery cloth

11 Procedure – Preparation  Prepare iron Plug in iron Dampen sponge Clean tip w/ sponge Apply solder to iron tip (tinning) Wipe excess solder Tip should be have silvery sheen

12 Procedure – Execution  Place component Bend leads to fit hole pattern Insert component through correct holes Clinch leads slightly outward to hold in place Attach heat sink if needed

13 Procedure – Execution  Solder component Wipe iron w/ sponge Apply tiny solder amount to iron tip  Not solder to form joint  Helps conduct heat properly Touch tip side to BOTH pad and lead Add bit more solder to form heat bridge Wait for joint to be heated (~1-2 sec)

14 Procedure – Execution  Solder component (cont.) Feed small solder amount from opposite side Molten solder should spread and fill joint Move solder away first Move iron away quickly Return iron to stand  Entire process ≤ 5 sec  Wait additional 3-5 sec for joint cooling

15 Procedure – Inspection  Inspect joint quality Good joint  Shiny  Bright  Smooth  Concave solder fillet  Good wetting

16 Procedure – Inspection  Inspect joint quality (cont.) Bad joints  Balled up or spiked  Dull color  Crystalline or grainy looking  Convex solder fillet  Dewetted Causes  Dirty leads, pads  Movement during cooling  Overheating

17 Procedure – Finishing  Return iron to stand  Cut excess lead length  Clean residual flux w/ alcohol Prevent future oxidation Prevent unwanted electrical shorts

18 Techniques - Desoldering  Repair bad joints  Remove solder bridges Excess solder connects two pads, leads Unwanted electrical connection formed  Remove components  Both require old solder removal Place solder wick against solder joint Heat wick opposite side from joint Solder should wick up braid Remove braid first Remove and return iron to stand

19 Techniques – Wire Tinning  Must tin wires before soldering to components, board Attach heat sink just below insulation Heat wire end Touch solder to wire opposite iron tip Solder should wick up wire Too much heat damages wire insulation

20 Conclusion  Introduction Definition Equipment  Procedure Preparation Execution Finishing  Specific Techniques Desoldering Tinning

21 References      itp.nyu.edu/physcomp/Tutorials/SolderingAPerfBoard         us.geocities.com/steves_workshop 