Doesn't the IPC call for simple coverage?  Meaning that as long as the pas
is wetted and covered solderability should be acceptable. We still do
solderability testing on coupons prior to assembly and that will usually do.
Just my two cents,

Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]

-----Original Message-----
From: Franklin [mailto:[log in to unmask]]

Tom,

I recommend using extreme caution on outlining min-max for HASL. By nature
this process is not the easiest to control.

One thing that I have seen is minimums being called out by themselves.

When all conditions are optimal with the process (HASL) you may still find
variation from pad to pad, and occasionally within a single pad, of
75micro".

With plated Sn/Pb you have greater control over thickness, after reflow the
solder flows in a certain manner as to cause highs and lows. This is normal
and should be considered when developing such tolerances.

My suggestion, work with your board shop, evaluate what works best for your
applications. The both of you identify what tolerances are both consistently
achievable, and acceptable.

And as a side note, if you set these limits, and a single pad or two out of
500 pads are outside of those limits, let's say by
20 micro", is the board acceptable? not acceptable?

Just some things to think about.

Franklin D Asbell

 -----Original Message-----
From: Tom Oliver < [log in to unmask]
<mailto:[log in to unmask]> >

Good Morning
Again I am looking for some help. We visited 4 different board shops last
week and got some good feedback on our solderability issues.
One of the things they stated is if the thickness of HASL drops below 50
micron/ microinches I am not sure which, it would affect solderabilty.
I have looked thru the IPC specs on Boards and solderability and have found
nothing on the min and max thickness for the solder. We use 63/37 solder
surface on our boards.
We are thinking of putting a min thickness spec on our B/P's is this
feasible or not. Also what is the standard that relates to this or the
industry standard that is used?
Thanks in advance

Tom Oliver

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