Richard,
I am trying to determine mass influence on reflow. I have attached
thermocouples to a bare board (dense 18 layer PCB with around 15 or 20 BGAs
(fine and micro) and have attached thermos to a board with around 5 or so
BGAs and have logged results. Now I'm trying to find total component mass to
arrive at a final reflow recipe. I don't have spare PCBs to play with, so
I'm trying to take a scientific approach. Basically I know that a bare board
gives me a certain peak with a certain time over liquidus. Now with about
10% of the "mass" parts loaded, I get a lower peak and shorter time over
(due to sinking). If I can determine total mass, I can use deductive
reasoning to get pretty darn close by using ratio theory. Remember, if A
equals B, and B equals C, then A MUST equal C.
If I can say that board A (bare board - no parts loaded) gives me a peak of
240 and time over of 50 sec; and board B with 10% "mass" loaded gives me a
peak of 232 with time over of 43 sec.; then if I can find the total mass
(already knowing the mass of the 10% loaded board) then I can use a ratio to
find what the total loaded board will yield in terms of peak and time over.
Then I can infuse higher temps and slower belt speeds to get close.
WOW! What a ramble.
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stadem, Richard
Sent: Thursday, September 29, 2005 2:57 PM
To: [log in to unmask]
Subject: Re: [TN] Okay, all you real smart guys.........
You need to subtract the weight of the solder from the delta of the
assembly minus the pwb to get the true weight of the components.
May I ask why you are trying to determine this?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant
Sent: Thursday, September 29, 2005 2:51 PM
To: [log in to unmask]
Subject: Re: [TN] Okay, all you real smart guys.........
The weight of the populated PCB minus the weight of the bare PCB will
give you the total or combined weight of the components. But if you
want the weight of individual components, you're going have to actually
measure each one...:(
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jason Gregory
Sent: Thursday, September 29, 2005 1:42 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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