Doug:
Thank you for the thorough update.
Surface mount reflow is certainly a major issue. And, as you've pointed
out, there is no need in that process for components to reach
temperatures 40°C above the melting point of the solder.
Wave soldering presents different conditions. If we switch from eutectic
tin/lead in wave solder baths, the additional heat is almost certainly
necessary (though I continue to wonder how well the replacement alloys
will perform with respect to issue such as bridging and solder spikes
even with the higher temperatures). Do you have any thoughts or test
results relating to that process?
Jim Smith
Managing Director
Cambridge Management Sciences, Inc.
4285 45th St. S.
St. Petersburg, FL 33711-4431
Tel: (727)866-6502 ext. 21
Fax: (727)867-7890
eMail: [log in to unmask]
> "Romm, Doug" wrote:
>
> Jim,
>
> You have touched on a very important issue in the transition to
> lead-free. Some of the lead-free solders (specifically SnAgCu) have a
> higher liquidous temperature than SnPb. Most folks have taken the
> liquidous temperatue of SnAgCu (217-221C) and added 40C to come up
> with a 'worst-case' peak reflow temperature of 260C. Our work (as
> well as the work of others) has shown good soldering performance of
> SnAgCu when reflowed in the range of 235-240C. However, the idea of
> using SnAgCu solder alloy and attempting to maintain a lower peak
> reflow (235-240C) has not 'taken off' in the industry. It appears
> that 260C capability for plastic packages will be a necessity.
>
> Earlier this year, TI along with several other component suppliers
> characterized moisture sensitivity performance of their components
> when using a 260C peak reflow. This consortia found that moisture
> sensitivity performance generally drops 1-3 levels (sometimes more)
> when using a 260C peak reflow temperature with current (early 2000)
> assembly material sets. The impact of the 260C peak reflow varies
> depending on the particular package tested. This information was
> communicated to the industry through a technical paper presented by
> Mark Kwoka of Intersil at IPC Works 2000 in September.
>
> In separate work, TI has found that our most advanced packages
> (TSSOPs, TVSOPs) show positive results when tested at a peak reflow of
> 260C and can likely achieve level 1 moisture sensitivity at 260C, thus
> requiring no change to current moisuture sensitivity classification.
> This data is still preliminary. We are actively working on 260C
> capable material sets for older technology packages also. We expect
> to have a solution to the issue of 260C capability before lead-free
> soldering processes become the norm.
>
> As for the TI position/status you can view our web page at
> http://www.ti.com/sc/leadfree. This page contains much technical data
> on our lead-free component finish options and is in the process of
> being updated now.
>
> Regards,
>
> Doug Romm
> Member Group Technical Staff
> Texas Instruments
> [log in to unmask]
>
>
> -----Original Message-----
> From: Jim Smith [mailto:[log in to unmask]]
> Sent: Monday, December 04, 2000 3:04 PM
> To: [log in to unmask]
> Subject: [LF] Component Durability
>
> Pondering some recent postings on this forum, I began questioning some
>
> of the assertions that eliminating lead is feasible. Specifically, I
> wondered about the current inability (or, at least, lack of rating) of
>
> many parts to survive temperatures in the 260°C range (many larger
> ceramic capacitors, for example, are not warranted to survive
> immersion
> in solder above approximately 230°C for even a few seconds). If lead
> is
> removed from solder, the components will be required to survive at
> 260°C
> or higher for quite a large number of seconds.
>
> If the components can be made to tolerate higher temperatures without
> degradation when new solder(s) with higher melting temperature(s) are
> introduced, why haven't component manufacturers already made their
> devices more robust?
>
> Jim Smith
> Managing Director
> Cambridge Management Sciences, Inc.
> 4285 45th St. S.
> St. Petersburg, FL 33711-4431
> Tel: (727)866-6502 ext. 21
> Fax: (727)867-7890
> eMail: [log in to unmask]
>
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