We have also done extensive studies on the HASL process and I agree with 
   Mr. Holmes 100%.
   
   Dennis Mitchell
   Zycon Corp.
   [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Re: FAB: Fine Pitch solder thickness w/HASL
Author:  [log in to unmask] at corp
Date:    4/2/96 10:40 PM


We have spent a lot of time studying the HASL process, and in my opinion it is 
virtually impossible to control solder thickness within tight tolerance.  The 
lower limit of solder thickness on surface pads is generally between 50 and 
100 microinches.  Thick areas elsewhere on the same board often exceed 1.5 
mils.
   
The lower limit you specify is unrealistic, and unneccessary.  0.3 mils 
applies to plated solder and is not needed with  HASL.  The real requirements 
for reasonable shelf life is no exposed intermetallic.  This can be achieved 
at a minimum solder thickness around 50 microinch.
   
Robert R. Holmes
Lucent Technologies (Formerly AT&T)
[log in to unmask]
   
   

------------- Begin Original Message ------------- 
From: rfpo2.rfc.comm.harris.com!njd (Dill, Norm J) 
Date: Mon Apr 01 11:13:00 EST 96
Subject: FAB: Fine Pitch solder thickness w/HASL
To: [log in to unmask] ('IPC Technet Input') 
Cc:
Bcc:
Content-Type: text     
Content-Length: 732
   
   
    Our HASL solder thickness spec. is 0.3 to 1.5 mils.  Is it unreasonable 
to expect using a horizontal HASL process that 1.5 mils will be the actual 
max. on 100% of the pads on both sides of the board, even with fine pitch (< 
= 20 mils)?
    My guess is that the surface tension of the molten solder on the fine 
pitch pads, its low mass and the surrounding geography, make it difficult 
for the air knives to do consistant leveling.
    Some of our product mix here is Mil Spec work.  Converting the boards 
with fine pitch on both sides to Au/Ni may be more pain than it is worth.
    Any inputs on this subject will be greatly appreciated.
   
Norm Dill
MQC Specialist
[log in to unmask]
(716) 242-4210