The BGA will be properly heated because the IR unit supplies infrared to
both the bottom side of the board and to/through the component substrate to
the balls simultaneously, where the hot air process starts with air on the
our side of the package and forces it inside. In the case of the bottom side
of the board, the heater is programmable so that you can ramp up the
temperature to mimic the proper profile of the component and the resulting
temperature will not harm the board, lands, etc. User programmable software
controls all aspects of the process, so that profiles can be created for
various components and board. Audible alarms are also used to alert the
operator when reflow temperature has been reached, and board supports can be
used to prevent possible warpage to the board. This IR system uses the same
principles that were used by early reflow ovens, except it is used on one
component instead of a whole board, and uses a slightly different IR
wavelength to eliminate variations in absorption rates due to the color of
the device package.
Paul Black
-----Original Message-----
From: JaMi Smith [mailto:[log in to unmask]]
Sent: Tuesday, January 07, 2003 3:41 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Station
Paul and Yannick,
Please see below,
----- Original Message -----
From: "Black, Paul" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, January 07, 2003 11:39 AM
Subject: Re: [TN] Rework Station
> Yannick,
~ ~ ~
> Ersa IR550A
> . . . This unit
uses a different
> technology than the others. While the other units rely on hot air to heat
> the BGA, the Ersa utilizes IR technology. The IR applies the heat more
> uniformly and directly to the part, and will not affect adjacent parts
> nearly as much.
While I know that you want to pump a large part of the heat into the BGA /
ASIC itself, and hence the balls / leads, doesn't this mean in a real and
practical sense that the board area immediately underneath a large BGA /
ASIC may not (will not) in fact be properly (pre) heated, with the exception
of any heat induced thru the board from the bottom by any bottom heater. (On
a thick board, won't any "bottom heating" need to be extensive enough to
offset the use or IR as opposed to hot air?)
How will this IR heating of the part relate to "hot air" systems (where hot
air circulates under the BGA) in terms of damage to the board in terms of
lifted pads and traces, etc.?
Where is their more chance of the average operator "screwing up" and
damaging the board, with IR or hot air?
Has anyone done any realistic analysis of this?
I ask these questions by reason of myself once having to rework 300 boards
in a very short turn around where each board required that 2 large ASICs be
removed and then replaced. My research showed that our company's prior
attempts at having similar rework done on similar products (DAT Tape Drives
for the PC market) yielded several hundred thousand dollars worth of damaged
and unusable product due to severe damage to boards by the lifting of pads
and peeling up of traces. I successfully aquired and used a "hot air" type
of system to perform the job successfully with absolutely zero damage, but
learned in the whole process and experience that any rework system has its
drawbacks and limitations, and more specifically, its own requirements for
operator proficiency, and margin of what I call forgiveness, before it
trashes the board.
In other words, I would try and find out just how easy it is to "screw up"
with each of these different systems that you are evaluating, and possibly
talk to some users of these different products and find out just what the
nuances and sensitivities of each of the systems are. This may seem like an
odd approach, but it may be helpful in finding the best rework system in the
long run.
Ask some of these questions now, and it may save having to make excuses to a
customer in the future when you damage some of his products because you
chose the wrong system.
Hopefully food for thought,
JaMi Smith
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