Sorry Phillip,
The peak and time over were hypothetical. My actual delta was around 6
degrees.
I was able to guess (educated) at the settings and the results were actually
very, very nice.
As far as only needing three probes needed to determine the reflow, I must
disagree somewhat. If I probe the largest mass component on leading,
smallest mass on trailing, and largest near center, I am eliminating the
facts of what the other 20 heavy mass BGAs will do to the rest of the board.
They, of course, will cool the entire assembly due to their sinking effects.
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]
-----Original Message-----
From: Phillip Bavaro [mailto:[log in to unmask]]
Sent: Friday, September 30, 2005 12:35 PM
To: TechNet E-Mail Forum; Jason Gregory
Subject: Re: [TN] Okay, all you real smart guys.........
Hi Jason,
ok, after all the abuse you have gotten, I'll try to answer your real
question.
Your original question was oriented towards determining the mass of the
components (which has already been answered) but now you are asking a
question that indicates you are trying to set up a reflow profile for a
loaded board but only have a bare board to prep with.
First of all, your conveyor speed appears to be way too fast.
Second, you mention peak temperature but only refer to one measurement out
of five thermocouples attached. The goal is to get all five within 3
degrees of each other.
Third, the measurements have to include the largest mass component near
the leading edge and the smallest mass component near the trailing edge.
Also pick the absolute largest mass component on the assembly and
thermocouple it. This means you only need three parts to run your pre-test.
Now for the smart guy answer......
Tell me the weight in grams of the bare board, its length, width, and
thickness, the weight of all the components to be reflowed, and your reflow
oven make/model, and the alloy of the paste to be used, and I will tell you
the oven settings to try.
Phil
Jason Gregory <[log in to unmask]> wrote:
RE: [TN] Okay, all you real smart guys.........John,
With this assembly, I don't have a "profile", fully loaded, PCB to play
with. My thought is this (theory only): Let's say I have a board that
has
only 20 BGAs, nothing else on it, and they are all the same size,
package,
etc. If I run a bare board and get a peak temp of 240 and time over
liquidus
of 45 sec. then I run a board with half of the BGAs, 10 of them, and I
get a
peak temp of 230 and a time over of 40 sec., I could then surmise that
with
a totally populated board, all 20 BGAs on it, would yield a peak temp of
220
with a time over of 35 sec. This wouldn't be totally accurate...there
are
other factors, but I would get in the ballpark (since baseball crept in
this). If I lost 10 degrees peak and 5 sec. over liquidus per 10
components,
I could follow this theory to determine the results with all 20
components.
(?)
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]
-----Original Message-----
From: John Burke [mailto:[log in to unmask]]
Sent: Thursday, September 29, 2005 4:33 PM
To: 'TechNet E-Mail Forum'; 'Jason Gregory'
Subject: RE: [TN] Okay, all you real smart guys.........
OK,
I just got back from vacation and am not yet "with it", but my question
is
why on earth would you want to know?
It is obviously not for shipping since you do not want the board weight.
It can't be for RoHS since that is calculated at the homogenous material
level.
Do you have yet another regulatory requirement that we are all about to
be
subjected to??
Do tell,
John
------------------------------------
Avanex
John Burke
Senior Manager RoHS Compliance
[log in to unmask]
40919 Encyclopedia Circle
Fremont
CA 94538
tel: 510 897 4250
fax: 510 979 0189
mobile: 510 676 6312
------------------------------------
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jason Gregory
Sent: Thursday, September 29, 2005 12:42 PM
To: [log in to unmask]
Subject: [TN] Okay, all you real smart guys.........
Can someone point me in the right direction on determining mass of
components of a PCB, knowing:
the weight of a bare PCB
the weight of a populated PCB
number of terminations
etc.
Who knows the formula?
TIA
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]
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