finding leaded SMD parts - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: May 13, 2014, 08:05:50 pm
content: I was advised to use leaded SMD parts to help parts survive shocks without shattering, but I can't find any on farnell, am i using the wrong terminology ?

author: Christopher
author_rank: Frequent Contributor
timestamp: May 13, 2014, 08:10:23 pm
content: RTV Silicone and Non-slump (black araldite gloop) helps with big chunky transformers etc. To an extent concoat can help too.I'm not sure what you mean by leaded smd parts, though. But that could be my inexperience.

author: KJDS
author_rank: Super Contributor
timestamp: May 13, 2014, 08:19:54 pm
content: The biggest proponent of unleaded in its early days was Motorola, who found that it's mobiles survived shocks much better because unleaded solder was stronger than leaded. I've not had issues with either leaded or unleaded SMDs for space applications. The only higher vibration work than that I've done was for a fuze, and there everything got very specialized.You could try phoning Welwyn tomorrow to see if they still make any.

author: Simon
author_rank: Unknown
timestamp: May 13, 2014, 08:20:49 pm
content: I have no large parts like transformers but allegedly this thing has to withstand 500G of acceleration so the board could flex

author: Simon
author_rank: Unknown
timestamp: May 13, 2014, 08:22:20 pm
content: Quote from: KJDS on May 13, 2014, 08:19:54 pmSorry i meant parts with leads like soic chips have, I'll be using leaded solder as it's military anyhow.

author: Christopher
author_rank: Frequent Contributor
timestamp: May 13, 2014, 08:42:55 pm
content: By leaded SMD parts I thought you meant some kind of through-hole SMD part, didn't even think of Pb

author: Simon
author_rank: Unknown
timestamp: May 13, 2014, 08:44:03 pm
content: in fact I'm not talking about solder lead but wire leads on SMD parts

author: scientist
author_rank: Frequent Contributor
timestamp: May 13, 2014, 09:05:39 pm
content: Rather than, say, QFN footprints? Probably because the leads are more flexible and resilient than just a solder joint.

author: SeanB
author_rank: Super Contributor
timestamp: May 14, 2014, 07:21:25 pm
content: So diodes have to be MELF packages and the resistors the same as well.

author: Kjelt
author_rank: Super Contributor
timestamp: May 14, 2014, 08:57:29 pm
content: Quote from: SeanB on May 14, 2014, 07:21:25 pmI do not understand.Melfs are round so have less contact surface then regular packages, how would that help withstand 500Gs ?I would think that glueing the smd parts with appropriate glue would be more beneficial?

author: Niklas
author_rank: Frequent Contributor
timestamp: May 15, 2014, 12:37:59 am
content: You can solder lead free components with leaded solder or solder paste.Murata has some notice in many of their datasheets about checking the soldering quality when using reflow soldering with a "low temperature profile", i.e. using SnPb. With low temperature they mean a peak temperature below the melting point of pure Tin (232'C).Some SnPbAg solder pastes are possible to solder using a Lead free soldering profile without damaging the flux.

author: envisionelec
author_rank: Frequent Contributor
timestamp: May 15, 2014, 01:15:54 am
content: Quote from: Kjelt on May 14, 2014, 08:57:29 pmActually, MELF is a high reliability component. They're used in great numbers of military and automotive applications. When conformal coated (non re-enterable), they're not going anywhere at 500G.