Dear Alan,
your suggestion is very useful indeed. I think it makes geat sense to define
a common test vehicle with a range of the most regularly used components. I
also support the integration of SIR test structures, because the flux
residue activity will be a delicate issue with new lead free solder pastes
and higher soldering temperatures. I would like to share the little
experience we have so far with test board designs we tried for our seminars,
but which we are now also adapting for lead free process trials. Our main
focus lies on rework/repair and visual inspection. We have not entered
microvia technology with our testboards. But what we have done is entering a
four layer test board into the game, which makes a tremendous difference due
to the in-plane thermal conductivity of inner layer copper, to be or not to
be there!
If you want to learn more about this board please contact my collegue Helge
Schimanski at the following e-mail address: [log in to unmask] . The
board is "euro size", i. e. 100mm x 160mm, standard 1.4mm thick and contains
PLCC68, TQFP144, various BGA and CSP footprints, plus arrays of passive
components with size 0402 and 0201, to study the effect of the new lead free
solder profiles on the smallest of all components in size and heat capacity,
which appear most sensitive to metallization leaching especially during
repeated melting (during rework of neighboring IC components). In terms of
the components, we have tried to use those which are readily available from
component or dummy manufacturers, although we had to find out the hard way
that internet offers do not necessarily mean hardware availability (e. g.
when you ask for lead free BGA).
We have integrated SIR test structures according to IPC suggestions under
components, also using the component leads as electrodes (non-daisy-chained
dummy components have to be used in this case). The inner copper layers can
be used here in an elegant way to makes contact to edge connectors (although
for SIR test these edge contacts should be soldered). For projects-to-come
we have ordered test boards in standard electroless Nickel - immersion Gold
as well as in electroless tin finish, and we have FR4 as well as FR5. Do you
consider this a push in the right direction, or is this variation in the
base material not appropriate at the moment? I'd appriciate your comments on
this.
Best regards,
Thomas Ahrens, Memellandstr. 8, D-24598 Boostedt
Tel. ++(49) (0) 4393 97769 e-mail [log in to unmask]
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-----Ursprüngliche Nachricht-----
Von: Alan Rae <[log in to unmask]>
An: [log in to unmask] <[log in to unmask]>
Datum: Freitag, 28. April 2000 13:29
Betreff: [LF] Test board frustration!
>We are starting a program at Cookson Performance Solutions to assess the
>cross-compatibility of lead-free products and processes - laminates,
>innerlayers, surface finishes, solders, fluxes in reflow and wave. The
issue
>is, we have asked people for appropriate test vehicles...and we're up to 20
and
>counting. Some are extremely complex and it is not unusual to see a
matrix
>where for for one program alone the boards and components cost is in the
tens of
>thousands of dollars. There is no standard basic test vehicle which means
that
>most published results are not comparable.
>
>This is what we propose as a first step.
>
>We think we need a minimum of two very basic test vehicles to assess
>performance:
> One for reflow with one side regular pitch and one side fine pitch
(these may
> not in fact be compatible as ultra-fine pitch might need microvia
technology,
> pushing us to three boards).
> The second with mixed technology that can handle wave or pin in paste
reflow
> - rather like the dummy modem board we produced at Productronica.
>
>We think we need to standardize, apart from the basics (tooling holes,
>fiducials, part number and revision level, labelling area)
> 0.062" thickness
> Daisy chain components
> Edge connector for electrical testing
> SIR test pattern
>
>The boards would be subject to the usual destructive and non-destructive
testing
>of solder joints after environmental exposure.
>
>Based on your comments and an analysis from our statistician on how many
>components would be needed for meaningful results we plan to design the
boards
>and make the designs freely available to whoever wants them. They could be
>adapted to be industry standards (or be superseded by industry
standards...but
>we have to start somewhere?)
>
>My question to the forum:
> Does this make sense to you?
> What have we missed in our analysis?
> Does anyone already have economic and effective test board designs
already
> that they'd be prepared to share with the industry? If so, can you
describe
> the board design and what it costs in board and components?
>
>Thanks in advance for your input!
>
>Alan Rae
>Director of Technology
>Cookson Electronics
>Foxborough MA
>508-541-5843
>
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###############################################################
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