Product evaluation includes assessment of functional and visual requirements of the weld. Weld analysis is most efficiently done in the design stage where the part design and process have not been finalized. The first step is to establish weld performance requirements such as strength, fatigue life, corrosion resistance, and electrical resistance. In some applications, such as for medical devices and appliances, visual appearance of the weld may also be important such as avoidance of discoloration.
Strength is perhaps the primary requirement of any weld/solder/braze. Even if the part is not load bearing, such as a solder connection, the joint has to have enough strength to withstand handling. Most joints do have strength as a functional requirement since they are intended to carry a load. The load applied on these welds can be in the form of tension, compression, torsion, fatigue, or vibration. A good understanding of exact mode of loading is very helpful in selection of part design and materials.
Quite often, the weld is exposed to high temperatures after the welds are made. The high temperature exposure may come during a follow-on operation, such as in an injection molding machine, or when the part is used near a high temperature source such as an automotive engine. Such temperature exposure is not obvious and can be difficult to anticipate.
Corrosion is another functional requirement which may not be obvious. Atmospheric precipitation in crevices of weld joint can cause rapid corrosion. Exposure to salts and other chemicals can accelerate the corrosion problem
Electrical requirements are often the primary concern in solder joints and welds in electrical applications such as circuit boards, solar cells, and interconnects. Joint performance in terms of current density, heat generation, and life need to be well understood before proceeding to the next step of designing the part.