lead free solder on regular HASL pads - Page 1
Forum section: electronics / beginners

author: kellogs
author_rank: Regular Contributor
timestamp: October 02, 2021, 10:35:51 pm
content: Re: mixing lead solder with lead free solderQuote from: free_electron on November 21, 2012, 08:02:10 pmQuoteThis just begs the question: Why would then so many engineers prefer ENIG pads, which, supposedly, goes with both leaded and lead free solders ?

author: tooki
author_rank: Super Contributor
timestamp: October 03, 2021, 10:20:05 am
content: ENIG doesn’t oxidize (unlike bare copper, and to a lesser extent, pure tin), and it’s perfectly flat (unlike HASL).The amount of gold is so tiny that for nearly all applications it’s irrelevant. For high-reliability applications like spacecraft, it’s standard procedure to tin the gold pad, then suck off the gold-contaminated solder before use.

author: kellogs
author_rank: Regular Contributor
timestamp: October 03, 2021, 10:26:56 am
content: Does that mean it is fine to use lead free solder on regular HASL pads for non-spacecraft applications ?

author: wraper
author_rank: Unknown
timestamp: October 03, 2021, 10:29:52 am
content: Quote from: tooki on October 03, 2021, 10:20:05 amIt's not a standard practice and cannot be done without severely affecting pad flatness and causing ionic contamination. This is done only with component leads where gold layer is an order of magnitude thicker than ENIG.

author: wraper
author_rank: Unknown
timestamp: October 03, 2021, 10:33:30 am
content: Quote from: kellogs on October 02, 2021, 10:35:51 pmRemains solderable for longer, is always perfectly flat and less ionic contamination. HASL sucks for fine pitch and BGA.

author: tooki
author_rank: Super Contributor
timestamp: October 03, 2021, 10:58:13 am
content: Quote from: kellogs on October 03, 2021, 10:26:56 amYou should order lead-free HASL if you’re going to use lead-free solder.

author: tooki
author_rank: Super Contributor
timestamp: October 03, 2021, 11:06:24 am
content: Quote from: wraper on October 03, 2021, 10:29:52 amNope, not in current standards: they say that gold shall be removed “From 95% of all surfaces to be soldered of surface mount componentsregardless of gold thickness.”https://www.eptac.com/j-std-001-revision-changes-regarding-the-requirements-for-gold-plating-removal/https://globalsmt.net/articles_&_papers/getting-gold-critical-requirement-high-reliability-applications/

author: wraper
author_rank: Unknown
timestamp: October 03, 2021, 11:56:23 am
content: Quote from: tooki on October 03, 2021, 11:06:24 amAnd where it says PCB? If you mean gold thickness on the component leads, I wrote not about standard but that gold plating on the leads is much thicker than ENIG (except cheap connectors which won't be used in aerospace anyway).

author: tooki
author_rank: Super Contributor
timestamp: October 03, 2021, 12:29:11 pm
content: Absent the full text of the standard, we can’t be certain what the intent is. For sure the thick gold on connectors, etc is the major concern.

author: kellogs
author_rank: Regular Contributor
timestamp: October 05, 2021, 10:16:59 am
content: Do specific fabhouse lead-free HASLs call for specific lead-free solder pastes then ? Or, perhaps, maybe some of the solder paste formulations are easier to work with on certain lead-free HASLs ?

author: wraper
author_rank: Unknown
timestamp: October 05, 2021, 10:28:46 am
content: Quote from: kellogs on October 05, 2021, 10:16:59 amI assume they generally use something like Sn99Cu (since pads look shiny) which should be safe to mix with SnCu and SnAgCu solders.

author: jeremy
author_rank: Super Contributor
timestamp: October 05, 2021, 11:11:52 am
content: Definitelydo notmix Pb solder with the low temp Bismuth-based solders (also there is the different melting point issues, but the alloy that forms is awful). Joint becomes very brittle due to strong intermetallic growth and easy to break with even what I could consider moderate force. For example, with the right (or wrong) mix of solder and a decent grip, I can pull SMD aluminium polymer caps off the board with my bare hands.I'm pretty sure remember reading a super old IBM article where they investigated this Bi/Pb mix for some temperature sensitive parts in a mainframe, and it was a disaster. Can't find the article now thoughAlso fromhttp://www.surfacemountprocess.com/low-temperature-lead-free-solder-paste.htmlQuote

author: kellogs
author_rank: Regular Contributor
timestamp: October 05, 2021, 01:42:37 pm
content: Since it has ads all over the site... my fab house is JLCPCB. They have already answered that there is no recommended solder paste formulation for their LF-HASL.Quote from: jeremy on October 05, 2021, 11:11:52 amOf course not to mix anything! Actually, this is the first reference that I see advertising safety to mix alloys of any nature. Would be pretty neat for my case, very helpful. Oh, and for SMD electrolythics - I can pull them out of pure low temp SnBi alloy without a problem.

author: xavier60
author_rank: Super Contributor
timestamp: October 05, 2021, 11:07:50 pm
content: I got some PCBs made by PCBWay with OSP treatment. The solderability is excellent. Yet to see if there is any deterioration during storage.OSP and even bare copper cost more than HASL.

author: kellogs
author_rank: Regular Contributor
timestamp: June 13, 2022, 08:11:50 pm
content: I still got a thought lingering in the back of my mind...I have not come across all that many datasheets specifying whether the part is meant for lead-only soldering or LF-only soldering. It seems this lack of spec allows both types of solder to be used with the part. The part being the same, it has the same sort of pads / pins....

author: wraper
author_rank: Unknown
timestamp: June 13, 2022, 08:32:57 pm
content: Quote from: kellogs on June 13, 2022, 08:11:50 pmLead-free parts can be used with both leaded and lead-free solder. Although some precautions may be needed when parts with thick layer of solder are used with leaded solder in high reliability equipment. Parts with terminal finish which contains lead shouldn't be used with lead-free solder.