INDUSTRIAL INFO-TAINMENT Wiring Harness News MAY / JUNE 2022 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 ?
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 .
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 .
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 .
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 .