Subject: | |
From: | |
Date: | Fri, 27 Oct 95 17:27:36 EST |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
Regarding HASL thickness, here are the parameters that
my company adheres to. All measurements are taken at the
geometric pad center. We read every 50th panel coming off
of our horizontal leveller. Horizontal levelling helps to
more evenly disperse the solder and fights a pronounced
"north-south-east-west bias" on QFP's. The boards enter the
solder pot horizontally cocked at 45 degrees.
.025" pitch or less = .00008" - .001"
.050" pitch = .00007" - .001"
discretes = .00005" - .001"
This shows that solder thickness is dependent upon pad
geometry; i.e., the greater the area for the solder to
retreat onto, the thinner the solder tends to be. I should
add that in all cases, HADCO guarantees solderability.
Concerning scoring, make sure that your fabricator does
simultaneous scoring (V-grooves from both sides at the same
time), and not flip scoring. I say this because boards have
a thickness tolerance, .062" (+/-.007") for instance. This
means that the end user will accept a .055" thick board, a
.069" thick board, or anything inbetween. Spec out your
remaining board thickness after scoring and this will
prohibit flip scoring. Here are the parameters that we
recommend:
.062" thk bds. = .012" (+/-.002") remaining thickness
.031" or less = .010" (+/-.002") remaining thickness
Of course, depending upon the components used, you may have
to adjust this (i.e., heavy components may cause you to beef
up the remaining thickness by .002" or so). Most end users
are now using some sort of fixturing when depanelizing
scored boards. This helps eliminate cracking peripheral
capicitors and such.
Regards,
Tom Coyle
Field Services Engineer
HADCO Corporation
|
|
|