Ask Helena & Leo

Question: While reviewing IPC-A-610, Section 4.1.5.1 (Torque of Threaded Fasteners), the question of “what is the standard industry practice” came up. I checked several reference documents like IPC-AJ-820 but found nothing that explained this to any length. Can you explain what the “standard industry practice” is?

Answer: The IPC-A-610 document is an acceptability document for the assembly of electrical components to printed circuit boards and securing them with solder, so Torque is not a common element of fastening things to printed board assembly processes. Torque is used in manufacturing of mechanical assemblies where parts have to be assembled together with hardware like nuts, bolts, screws and such.

There are typical Torque requirements used in those processes which have been put together by mechanical and metallurgical engineers. This is due to the various metals being put together and the relative hardness and hardware used to secure the parts.

The intent of putting Torque requirements in IPC 610 was to make mention of the fact that something had to be defined if hardware was used to secure the product to chassis and boards, which is why it was added to the 610. The amount of Torque to be used is left to the design and manufacturing engineers who will define the hardware to be used and the amount of force is to be used to assemble those parts to the product.

I’ve added a couple of web sites for you to review about what the Torque value should be depending upon the diameter size of the screw, nut or bolt.

1.      http://www.qualitymag.com/articles/87967-the-basics-of-torque-testing
2.      http://www.boltscience.com/pages/quality.htm
3.      http://www.holo-krome.com/pdf/torquedatachart.pdf
4.      https://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf

This should hopefully point you in the right direction.