As usual I agree with Dave Hillman and Rich Stadem.  Like I've said many times I'm an old timer and I began life with HASL and grew up with all the alternative.  During the implementation of fine pitch surface mount products there were two things we used to say about HASL; 1). HASL can be solderable or 2). HASL can be flat.  You can adjust the HASL air knives to leave some SnPb on the features in the case of SnPb HASL or to leave some Sn on the features in the case of Pb-Free HASL which will allow the features to be solderable.  However, the topography of the features may not be flat and you have a "soldering" rather than a "solderability" problem.  Or you can adjust your air knives to blow off most or all of the SnPb or Pb-Free solder leaving only a very thin solderable layer or in some case leaving only the IMC.  This makes the features very flat and you can print solder paste on them and place fine pitch components.  The problem with flat HASL is the IMC is on the surface or over times grows through the tin solderable coating and then the IMC is exposed to the environment and it oxidizes and becomes un-soldereable.

So everyone wanted flat HASL but they also wanted solderable HASL and they soon realized they couldn't have both so they looked for alternatives to HASL.

George

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Tuesday, January 23, 2018 10:59 AM
To: [log in to unmask]
Subject: Re: [TN] soldering problems

Hi Bob - the primary disadvantage for HASL is flatness and secondary is long term solderability. For automated SMT reflow, the immersion finishes ((ImAg, ImSn, ENIG) have a flatness advantage that is good for fine pitch BGA, flip chip and small resistor/capacitor (0402s, 0201s, 01005s, etc.) assembly. And some HASL are better than others so there have been long term solderabilty issues documented. Again, both tin/lead or lead-free HASL are not bad finishes, they have applications where they work great and other applications not so great.

Dave

On Tue, Jan 23, 2018 at 9:48 AM, rkondner <[log in to unmask]> wrote:

> Bev and John,
>
>  Thank you. So that is two votes for flatness issues.
>
>  Any others?
>
> Thanks,
> Bob
>
>
> On 1/23/2018 10:27 AM, John Burke wrote:
>
>>
>>
>>
>>
>>                 I believe this is referring to “random highs” where 
>> most of the pads are relatively flat but on some the solder is still 
>> on the pad typically high in the direction of the air knife
>>
>>
>>
>>                 Sent from my iPad Pro
>>
>>
>>
>>
>>
>> On Tue, Jan 23, 2018 at 7:18 AM -0800, "BEV CHRISTIAN" < 
>> [log in to unmask]> wrote:
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Bob,
>> Please explain what in your case you mean by “warts”.  Did you mean 
>> that literally or as you using the term as Wayne was?  HASL is by its 
>> nature is not flat.
>>
>> I would contend that HASL flatness CAN be an issue that solder paste 
>> is not always going to fix.
>>
>> Regards,
>> Bev
>> HDPUG
>>
>> Sent from Mail for Windows 10
>>
>> From: rkondner
>> Sent: Tuesday, January 23, 2018 10:08 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] soldering problems
>>
>> Hi,
>>
>> Can someone explain to me the warts associated with HASL? I know some 
>> would say flatness but since solder paste goes on all my boards that 
>> is not am issue.
>>
>> I am an EE and I typically run 5 to 25 boards for protos. A run of 
>> 100 or 250 is a big job for me. I cannot keep up with validating 
>> every vendor. I cannot run and verify coupons for every run.
>>
>> HASL has been very good to me even with low cost vendors and simple 
>> board storage. What am I missing. (Other than soldering problems! :-)
>>
>> Thanks,
>> Bob K.
>>
>>
>> On 1/22/2018 7:25 PM, Wayne Showers wrote:
>>
>>> IAg is not a horrible idea for a surface finish, but it does come 
>>> with its own warts.
>>> 1) Creep Corrosion: DFR Solutions has done much research on this.
>>> Primary recommendation to mitigate it is to paste all component pads 
>>> whether populated or not.
>>>
>>>> https://link.springer.com/article/10.1007/s11664-004-0025-x
>>>>>
>>>> 2) Move away from WS fluxes.  Because RMA fluxes utilize the Rosin 
>>>> as a
>>> suspension agent, you will get must less secondary issues with the 
>>> flux penetrating into unwanted areas which include under the solder 
>>> mask, between plating layers (This is critical for immersion silver 
>>> as the silver immersion process creates micro-voids and 
>>> micro-pitting of the underlying
>>> copper.)
>>>
>>> 3) Storage and Handling: Always wear clean cotton or latex gloves 
>>> (preferred).  Cotton can trap oils and if the gloves are cleaned, 
>>> many detergents and fabric softeners have phosphor and sulfur compounds in them.
>>> And Silver saver paper is a must.  Silica desiccant and IAg are not 
>>> compatible.
>>>
>>> And as a final aside, unfortunately the days of Tin-Lead are limited 
>>> thanks to the tail wagging the dog over in the EU with Electronics 
>>> as the target.  In 22 years of Electronics Manufacturing, I have had 
>>> 4 issues with bad ENIG or ENEPIG plating, and Roughly 40-50 issues 
>>> with flux penetration or entrapment including 1 recall that totaled over $1.5 Million Dollars.
>>>
>>>