4 ms·

There are more mundane issues like lead-free solder. RoHS isn't US law and the military will not use lead-free parts because of reliability issues. Most DIL and

There are more mundane issues like lead-free solder. RoHS isn't US law and the military will not use lead-free parts because of reliability issues. Most DIL and QFP parts are sold with unformed leads because vibration requirements generally require higher standoff from the board customized for each application so the leads flex less and can be supported from below with elastoemric compounds. Good luck procuring such things without some significant cash and the right contacts.

iancmceachern 3y ago
I'm confused, you seem to be conflating pcbs and parts. The ics are soldered to the board with the lead, or lead free solder. The lead or lead free solder thing only applies to securing the parts to the board, the pcba assembly process, not the chips themselves. Am I correct? Makes sense on the lead height thing, the more you know.
- kevin_thibedeau 3y ago
  Leads that come pre-tinned have to have a compatible solder on them. When you buy components now, the suppliers declare whether they're RoHS (lead-free) or not. You can't easily buy eutectic (lead bearing) tinned parts anymore because it's easier to have the global supply chain conform to the EU regulations. Note that military parts often come with gold plated leads which you can use your choice of solder on. You can't easily buy such things anymore from commercial suppliers.
  - iancmceachern 3y ago
    Thank you!!
- coryrc 3y ago
  Not quite, the leads are (usually) coated with something. If it's pure tin it can grow whiskers from the top or even from under the solder connection, even if you use a leaded solder to attach it to the board. That's why even DIP parts come in leaded or lead-free versions. There are packages which come with the solder, like BGA, which can (usually?) safely be reballed to use leaded.
  - iancmceachern 3y ago
    Thank you!!!
  - pas 3y ago
    couldn't the whole PCB covered in some resin to prevent whisker formation?
    - coryrc 3y ago
      Metal is stronger than plastic

iancmceachern 3y ago

I'm confused, you seem to be conflating pcbs and parts. The ics are soldered to the board with the lead, or lead free solder. The lead or lead free solder thing only applies to securing the parts to the board, the pcba assembly process, not the chips themselves. Am I correct? Makes sense on the lead height thing, the more you know.

kevin_thibedeau 3y ago
Leads that come pre-tinned have to have a compatible solder on them. When you buy components now, the suppliers declare whether they're RoHS (lead-free) or not. You can't easily buy eutectic (lead bearing) tinned parts anymore because it's easier to have the global supply chain conform to the EU regulations. Note that military parts often come with gold plated leads which you can use your choice of solder on. You can't easily buy such things anymore from commercial suppliers.
- iancmceachern 3y ago
  Thank you!!
coryrc 3y ago
Not quite, the leads are (usually) coated with something. If it's pure tin it can grow whiskers from the top or even from under the solder connection, even if you use a leaded solder to attach it to the board. That's why even DIP parts come in leaded or lead-free versions. There are packages which come with the solder, like BGA, which can (usually?) safely be reballed to use leaded.
- iancmceachern 3y ago
  Thank you!!!
- pas 3y ago
  couldn't the whole PCB covered in some resin to prevent whisker formation?
  - coryrc 3y ago
    Metal is stronger than plastic