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March 2001

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Subject:
From:
Lisa Anderson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 19 Mar 2001 05:19:32 -0800
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Julien,
Depending on your board thickness and part type (our
typical is 10 layer, PBGA), stage your preheats to
slowly ramp the board up to approx 90C. Control your
nozzle air flow to 40% during preheat with nozzle temp
at 150C for both stages.  Soak increases to 50% 225C,
ramp and reflow up from that in both percentage and
temp. I set the bottom heaters to 400C during preheat
but then kick them down to approx 300C during other
cycles.  When you TC your package top are you milling
into the top material of the BGA (gives a more
dependable temp reading)?  The outer balls will always
reach reflow first due to nozzle design so TC your
inner balls.  Hope this helps.

Regards,
Lisa
--- Julien Bouchard <[log in to unmask]>
wrote:
> Hi everybody,
>         Two week ago, we got a big problem of BGA
> that do not work after the
> rework.  Almost all BGA fail after the rework.
> THe BGA is a 27mm x 27mm standard BGA,.  We have two
> reworks machine, an
> air-vac DRS24 and air-vac DRS22.  The problem only
> occur on the DRS24, which
> is the newest machine !  We modify the profil to
> lower the temperature, but
> my problem is that when i reach around 215 C in the
> join of the bga, the top
> of the bga body is around 235C, which is more than
> the recommanded
> temperature for BGA by the manufacturer.
>
> The profil we use is like :     preheat : 2 min at
> 60% of the flow and 250 C
>  the join reach around 165 C)
>                                         soak : 1 min
> at 50% of the flow and 290 C   ( the join reach
> around 180
> C )
>                                         ramp : 1.5
> min at 60% of the flow and 330 C  ( the join reach
> around
> 215 C )
>
> The BGA are keep in a dry cabinet to redust moisture
>
> Does is seem good ?  I not sure of the balance
> between longer time and lower
> temperaturer versus shorter time and hotter
> temperature. Anyone have
> experience with this.  Also, when you mesure the
> temperature, which ball you
> use : the inner or the outter ? The inner ball seem
> to be more hot than the
> other one. Also, for the people who have air-vac
> machine DRS22 and DRS24,
> have you problem of stability with the DRS24,
> compare to the old DRS22.
>
> Thank you.
>
> Julien Bouchard
> Matrox - Process Engineer
>
>
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