Huckl,
There are a variety of ideas of how to calculate actual surface
area, I like to use the spec from Bellcore TR-NWT-000078 as it is
overall more stringent for contamination levels than IPC/ANSI/MIL specs.
Section 14.5.2.2 specifies x2 surface area of one side for bare boards,
and x3 surface area for assembled boards. It also allows use of x2 +
actual surface areas of populated components, but my head hurts just
thinking of trying to calculate actuals of body, lead frame and other
contributors. So x3 it is for assembled boards. I have spoken with
'industry professionals' (who shall remain nameless), that have said
that they use x3 for single sided assemblies and x4 for double sided
assemblies.
One of the problems you have to deal with in automated systems
such as the Alpha SMD600 is that it will automatically calculate x2
surface are if you only provide length and width. You can prevent this
by entering your surface area directly into the 'area' field, and leave
the length/width fields blank.
Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX 77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]
> -----Original Message-----
> From: HUCKL CHANG, P.E./SHA 086-520-7314449.EXT.30156
> [SMTP:[log in to unmask]]
> Sent: Wednesday, November 04, 1998 11:42 PM
> To: [log in to unmask]
> Subject: [TN] FOR YOUR HELP
>
> Hi,
>
> Will you help me to answer the following question:
>
> Our company produce payment-transaction products, to ensure the
> quality we
> sampleing test its PCBA (print circuit board assembly) ionic
> contamination
> useing OMEGA METER 600-SMD before final assemble. While wanting to
> define
> the acceptance limit (unit: ug.NaCl/sq.in. the general is 14.0), we
> encounter the problem: how to calculate its total surface? In my
> opinion:
> Total surface area=level factor*2*bare board surface.
>
> Reason:
>
> 1. high density of component of PCBA can enlarges its "contamination
> surface", then times "level factor".
> 2. components lie on the both sides of PCB, then times "2".
>
> FYI--my company's PCBA manufactureing process:
>
> PCB side A print solder paste----->Side B through wave soldering.
>
> Although we have four volumes of IPC Standards and Specifications, I
> can't
> find the clear definition about PCBA ionic contamination test,
> especially
> how to calculate the total surface. Will you help to direct the
> information
> or offer your opinions?
>
> Thanks with best regards,
> Huckl Chang.
>
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