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Ask the Experts

June 22, 2011 - Updated
June 20, 2011 - Originally Posted

Lead to Hole Ratio for Lead Free

Are there any suggested differences for lead to hole ratios for leaded solder vs. lead free solder? Are there any suggested differences for through hole lead protrusion length for leaded solder vs. lead free solder?

C. S.

Expert Panel Responses

The hole to lead ratio subject has been covered a number of times in the past, generally due to the behaviour of the metals you can get away with a bigger ratio for lead containing than lead free. The added problem with Lead free is its reluctance to flow through the board to give a topside fillet. so a smaller ratio would hopefully give you a better chance of a fuller hole. Quality of the PWB, metalissation of the pads, outgassing of moisture and any cracks of deforming of the barrel of the hole will also impact solder flow. There would be no need to change the length of the lead protruding for the alloy, long enough to get a good joint but short enough to stop bridging or other defects, the IPC and other groups have done work on this in the past and it would be best to start with their recommendations then modify where necessary to overcome any defects you find.

Richard Boyle
Global Product Champion, Henkel Electronics

Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.

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