Wiring Harness News May-Jun 2022 - Page 57


The Problems With Tinning Wires

By James Dunbar Product Marketing Manager PCC , Phoenix Contact USA

Having problems with tinned wires coming loose in screw terminal block ? Many companies and manufacturers use the practice of solderdipping wire ends , but this can lead to loose connections . Beyond ensuring that all screws are tightened to the proper torque specification , this document shines light on why your tinned wires are coming loose .

Moving away from tinning and exploring other ways to prepare bare wire could save time and the headache of retightening connections .
Why tin wires ?
Stranded copper wires are commonly connected to PCBs or other devices with a screw-style terminal block . “ Tinning ” is the practice in which a stripped wire is coated with a thin layer of a tin compound . However , there is the associated problem of the wire becoming loose when used with screw-style terminal blocks .
One common reason for tinning is to prevent wire strands from fraying when connecting to the termination site . For example , stranded wires can be tedious to work with when pushing into the cage of a screw-type terminal block . In this case , there is the possibility for wire strands not to be pushed all the way into the cage , which could cause a short . If the wire will be frequently installed and removed from its termination site , the wire can become increasingly difficult to work with . Tinning might appear to be a good solution .
Why does tinned wire become loose in screw terminals ?
Root Cause
The root of the problem stems from when the wire is tinned and the tin material flows into the small space in between the copper stands of the wire . This makes the copper wire and tin into a solid mass of material .
Once the wire is inserted into the terminal block , and the cage closes and clamps on to a tinned wire , the tin / wire block is compressed and can change shape . In doing so , the tin can fracture and cause wire strands to pull apart from one another , creating voids ( Fig . 1 ). Essentially , as the wire is screwed down , it breaks apart the tin , which can start to loosen the wire . While the wire may be secure
initially , normal operation can cause the wire to become loose . Operation and Thermal Expansion
Figure 1 . Cracking of crushed solder
During operation , wires will heat up and cool down as the environment heats up and / or current flows through the wire . As the wire increases in temperature , thermal expansion can be the culprit behind loose terminations . The higher temperature in the wire and the tin material causes the metals in each of them to naturally expand and take up a larger volume . However , the material properties ( coefficient of thermal expansion ) cause the different metals to expand different amounts . In this case , the tin material expands more than the copper cage ( Fig . 2 ).
Figure 2 . Thermal expansion of solder .
As the metals cool , they shrink and take up less volume . The expansion and contraction can cause the shape of the tinned wire to change slightly , and no longer be properly clamped between the cage and pressure plate ( Fig . 3 ).
Figure 3 . Cooling and loose connection
Other Common Misconceptions
Tinning wires will increase corrosion resistance .
Yes … but when the tinned wire is compressed in the terminal , the tin breaks apart , so that the connection might no longer be gas-tight . Bare wire strands will create a better , gastight connection , and can be a more effective way of reducing corrosion .
Tinned wires will still fit into the terminal block .
In some cases , added material will prevent the wire from fitting properly in the block . Adding tin can make the

On average , a new automobile has approximately 40 electronic controllers , five miles of wiring , and more than 10 million lines of software code . Electronics , coils , and wires used in automobiles will expand to meet fuel efficiency and consumer standards .

In these parts , metal pins and wires are embedded in the plastic housing ( Figure 1 ). When the parts experience heat during manufacturing or normal use , the plastic and metal expand at different rates . This expansion creates microscopic voids between the materials . While these leak paths are unavoidable , they can cause a field failure if not sealed . The massive expansion of these parts in automotive electronic components has made sealing leak paths critical .
The two most common methods of sealing these voids are potting and vacuum impregnation . While potting is a popular method , the process has some disadvantages that vacuum impregnation addresses . Here are the three main reasons why vacuum impregnation is the preferred method to seal electronics .
Seal Leak Paths
Vacuum impregnation is a subsurface process that seals leak paths by filling the void between the two dissimilar materials . If not sealed , then fluids may penetrate the connector . wire larger than the terminal block is rated for . This will prevent terminal from properly closing / clamping on to the wire .
Final Thoughts
All things considered , tinning wires could be the reason for loose connections in screw terminal blocks . While tinning does have benefits , there are better alternatives that could save you the headache of loose terminations . A great alternative is to use ferrules and ensure the screws are tightened to the proper specification .

Three Reasons to Seal Electronics with Vacuum Impregnation

Figure 1 . Metal pins and wires imbedded in plastic housing .
Vacuum impregnation prevents fluids from leaking by sealing the leak paths .
Prevent Corrosion
From either oxidation or galvanization , corrosion reduces currentcarrying capacity and causes the part failure . Vacuum impregnation prevents corrosion by sealing the leak path that oxygen and moisture can follow .
Enable Design Freedom
Vacuum impregnation does not change the part ’ s dimensions , allowing engineers to design and make parts to the net shape . Since the process does not leave any sealant on the part ’ s surface , an engineer does not need to incorporate dimensional allowance ( Figure 2 ).
Figure 2 . No dimensional allowance needed for sealant .
In Summary
The surge in automotive electronics has made porosity sealing crucial . Properly sealing the porosity ensures the component ’ s quality meets its performance requirements . Vacuum impregnation is the most effective solution at sealing leak paths and preventing corrosion while enabling design freedom .
For more information on vacuum in pregnant and technology , visit godfreywing . com . Look for more information in future issues .