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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