=  NOW 30 WPM  =  TEXT IS FROM MAY 2022 QST  PAGE 46 =

ADHERE WELL WHEN IT COOLS.  BECAUSE COPPER DISSOLVES IN MELTED TIN, THE
SOLDER WILL FORM A THIN LAYER OF CU/SN ALLOY WHERE IT MEETS WITH COPPER,
FORMING AN EXCELLENT ELECTRICAL BOND.  FIGURE G IS ANOTHER POOR JOINT, MADE
WITH LEAD FREE SOLDER BUT WITH A 600 F TIP TEMPERATURE THAT IS, FOR LEADED
SOLDER.  THATS NOT QUITE HOT ENOUGH FOR THE SOLDER TO FLOW AND ADHERE WELL.
IN A JOINT LIKE THIS, THERE MAY BE ELECTRICAL CONTACT RIGHT AFTER
CONSTRUCTION, BUT AFTER SOME TIME THE CONTACT WILL BREAK A COLD SOLDER
JOINT AND THIS DEFECT MAY NOT BE VISUALLY OBVIOUS WHEN TROUBLESHOOTING THE
PROBLEM.  EVEN WORSE, THE JOINT MAY BECOME INTERMITTENT, MAKING IT EVEN
HARDER TO SPOT.  ITS ALSO IMPORTANT TO NOTE THAT SOLDER HAS VERY LITTLE
MECHANICAL STRENGTH AND WILL COLD FLOW IF IT IS STRESSED EVEN A JOINT
SOLDERED AT A PROPER TEMPERATURE CAN CRACK, COMPRESS, OR PULL APART IF IT
IS SUBJECTED TO MECHANICAL STRESS.  THEREFORE, IT IS GOOD PRACTICE TO MAKE
SURE COMPONENT LEADS, WIRES, ETC., ARE SECURELY WRAPPED OR BENT OR
OTHERWISE ANCHORED TO THE SURFACE THEY WILL BE SOLDERED TO BEFORE THEY ARE
SOLDERED.  THE PHOTOGRAPHS WERE TAKEN WITH A KKMOON 600X DIGITAL
=  END OF 30 WPM TEXT  =  QST DE W1AW  <