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Glossary of Terms

S


 

 Solder -

 

The most fundamental building block of a printed circuit board is SOLDER.

What is SOLDER? The most common type of solder used in electronics up until the RoHS Mandate in 2006 was 63% Tin and 37% Lead. Now days there are many different alternatives to solder containing lead... also much controversy regarding the reliability and whether or not the banning of lead in solder was such a good idea environmentally... see the lead free page for more info.

 

 

 
Mechanical Properties
Tin
(wt.%)
Tensile
Strength

(MPa)
Shear
Strength

(MPa)
Elongation
(%)
Elastic
Modulus

(GPa)
Izod
Impact
Strength

(J)
Stress to
produce
0.01%/day
creep rate

(kPa)
0 12 12 55 18.0 8.1 1700
5 28 14 45 18.5 9.5 1400
10 30 17 30 19.0 10.8  
20 33 20 20 20.0 15.0  
30 34 28 18 21.0 16.3 790
40 37 32 25 23.7 19.0  
50 41 36 35 26.9 20.3 860
60 52 39 40 30.0 20.3  
63 54 37 37 31.5 20.3 2300
70 54 36 30 35.0 19.0  
 
 
As can be seen from the above table, the 63% tin 37% lead solder alloy results in the maximum tensile strength, shear strength, impact strength, and resistance to creep. This 63-37 composition is also known as the eutectic point of the alloy, where the alloy behaves like a pure metal having a single melting (solidification) temperature (176C / 349F). This is a good operational feature. Once the solder melts on application of heat, it solidifies immediately on removal of heat, without going through a pasty stage like other alloys. This allows for predictable soldering and fast cycle times.
 
Physical Properties
Tin
(wt.%)
Specific
Gravity
Electric
Resistivity

(10-9ohm-m)
Thermal
Conductivity

(W/m-K)
Thermal
Expansion
Coefficient

(10-6/C)
0 11.34 212 34.8 29.3
5 10.80 207 35.2 28.4
10 10.50 204 35.8 27.9
20 10.40 192 37.4 26.6
30 9.66 180 40.5 25.6
40 9.28 166 43.6 24.7
50 8.90 153 47.8 23.6
60 8.52 145 49.8 21.6
63 8.34 144 40.9 21.4
70 8.17 134 30.0 20.7

 

Solder comes in many forms based upon the end use. Bar solder is extruded and shipped for use with solder bath or solder pot use or even Hot Air Solder Leveling or HASL machines. Solder Paste is used in screening applications for reflow oven soldering, Solder 'wire' is used for hand soldering with a soldering iron or pencil, by electronics hobbyists and assemblers and for rework. Aids to soldering like water soluble soldering flux, rosin core solders, different size soldering irons for different soldering jobs, cleaners, no-clean fluxes, solder wick for hand touch up or removal of solder, solder suckers, Also lead -free solders for compliance with the European RoHS directive due to be enforced after June 2006.

Much can be found on-line on the subject.

http://www.solderchemistry.com/en/solder.html

http://www.solderchemistry.com/en/lead_free.html

 
Solder Types
Many metals and their alloys can be used as solders. The following table gives a quick overview of various solder materials and their applications:

 

Solder Applications Characteristics
Bismuth Low temperature soldering Deforms easily. Needs Aggressive fluxes.
Cadmium-Silver High temperature applications Toxic. Good tensile strength
Cadmium-Zinc Soldering aluminum Toxic
Indium Low temperature soldering, wets glass Deforms easily
Lead-Silver High temperature applications Good high temperature properties, good fatigue strength. Medium or low flow properties
Tin-Antimony High temperature and food industry applications Non-toxic. Good high temperature properties. Better electrical conductivity and strength than tin-lead solders. Good wetting.
Tin-Antimony-Lead General purpose. Improved mechanical properties over Tin-Lead solders. Can not be used with zinc due to brittle zinc-antimony inter-metallic compounds
Tin-Lead General purpose, and the most widely used solders. Good process characteristics and the best understood solders.
Tin-Silver Used for soldering medical or high precision instruments. High temperature applications Non-toxic but expensive. Good high temperature properties.
Tin-Zinc Soldering aluminum  
Zinc-Aluminum Soldering aluminum  

 

 

 

 

 

 

 

 

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