Dear Paul,
Nice of you to challenge my knowledge rather than form quick opinions based
on guesses.
To answer your questions:
Temperatures listed were zone temps not board temps. The reason for these
zone temps are based on using a profile that includes a soak zone at 160C.
First two zones are going to give you a rise rate of approximately 1.6
degrees per second, rising from 23 C to 160 C (NOTE- the assembly is not in
zone 1 long enough to reach same temperature as the zone so there is not a
dip in the board temp) Then we hold at 160 C (or whatever the solder paste
manufacturers recommended soak temp is). After this the board temp rises to
approx. 215C as a peak temp. NOTE- different ovens have different numbers of
zones and different zone lengths. Our zones are 20" in length, the system
referred to has a total of 6 vertical zones.
Of course we offer cooling. The CUREFLOW (AKA Whoopee Flow) has 2 cooling
zones totalling 50 inches in length. The first 20" are a combination of
closed loop water cooling (which is also a part of the FLUX GRABBER, flux
condensation and filtration system) and forced air cooling. The last 30
inches is forced air cooling only. Cooldown rates are somewhat dependant
upon conveyor speed so I won't quote a number. Sorry I did not make that
clear the first time.
Please note that this profile recommendation is for solder pastes requiring
a soak at 160. Some pastes will require different soak temps and other
pastes can use the Tent style profile. In this case zone temps would be zone
1 - 120, zone 2 - 140, zone 3 - 160, zone 4 - 180, zone 5 200, zone 6 245
(of course this is based on a particular solder paste, zone temps would vary
depending on which no-clean you are using).
As far as top to bottom side temp delta's, how big would you like it? And
where would you like to measure it? I have run tests on a bare board as well
as a populated board. On a very thin bare board I measured a top to bottom
differential of 35 C with top side temperatures at 215 C +/- 1. When using
the same profile on a bare board I found that the same 35 degree board
surface differential became a huge difference when measured on the component
leads of a QFP located on the bottom of the board. Now measuring top board
surface temperature to bottom side component leads the delta was greater
than 50 C (easily more than enough to prevent second reflow of bottom
components). This delta could have been increase had I increased the speed
of our tangential RHA blower wheels. For this test I ran them at 1755 RPM's
and could have increased to as much as 2070 RPM.
I would be happy to discuss further if you like.
Sincerely,
Brian Stumm
ETS, LLC
3939 N. Freya St.
Spokane, WA 99207
509-483-0900 (voice)
509-483-0331 (fax)
[log in to unmask] (e-mail)
PS - what zone temps do you use on your Indium? The chiller you mention, are
you referring to actual refridgerated air or ambient forced air?
>Hi Brian
>Agree, the chiller you engage only when pushing limits , depends on top
>load componentry .
>Brian , enlighten me :
>165, 175, 160 (dip?) , 160(why?), 185, 245, ?(no cooling?) .
>Somehow my Indium profile looks different .
>What is the reason for dwell on 160 2x, and how do you cool ?
>With ALL bottom zones blowing ambient ; the separation is nice indeed .
>Can you get me an info on what ( in 'C's ) is achievable ?
>
>thanks
>Paul Klasek
>http://www.resmed.com
>
>> ----------
>> From: ETS[SMTP:[log in to unmask]]
>> Sent: Thursday, 25 June 1998 2:10
>> To: [log in to unmask]
>> Subject: Re: [TN] ASSY: BGA sanity check
>>
>> Dear Jerry,
>>
>> As a reflow manufacturer of course I want to brag but I also do not
>> blame
>> you for your hesitation. The weight of most BGA's outwieghts the
>> surface
>> tension of the solder paste. However, as Mr. Klasek pointed out,
>> reflow CAN
>> be avoided on the bottom side of the board. I am sure that you have
>> heard
>> before that once solder has been reflowed once the melting point of
>> that
>> solder increases to a higher temperature. This is where I have to
>> differ
>> with Mr. Klasek, we have not found chillers to be necessary. After
>> reflowing
>> the BGA's on the top side and inverting the board, we run the assembly
>> through an ETS CUREFLOW that has both top and bottom convection
>> heating. We
>> use a profile that uses standard temperatures on all 6 top zones
>> (165C,
>> 175C, 160C, 160C, 185C, 245C) and then set all bottom zones to ambient
>> temperature (or room temperature). This creates differential heating
>> on the
>> assembly by heating the top side of the board and cooling the bottom
>> side
>> of the assembly. This creates a big enough temperature delta to keep
>> the
>> bottom side components from reflowing a second time.
>>
>> Of course this method requires two passes through the reflow oven
>> whereas if
>> all the BGA's where on the top of the board you might be able to
>> solder both
>> sides with a single pass through reflow.
>>
>> If you would like to discuss this further I can be contacted at
>> [log in to unmask]
>>
>> Sincerely,
>>
>> Brian Stumm
>>
>>
>>
>>
>>
>> >Hello, TechNet....
>> >
>> >Soldering (inline convection furnace) BGA's on both sides of a board
>> is
>> >beyond my own experience, but it seems to violate a principle (at
>> least an
>> >imaginary one) related to the controlled collapse, or perhaps liquids
>> under
>> >tension.
>> >
>> >For a board design using 3 commercial BGA packages (PBGA 256,
>> eutectic
>> >balls on 1.27 mm pitch), am I obstinately blocking the path of
>> progress by
>> >requesting that this package style be confined to only one surface of
>> a new
>> >board design?
>> >
>> >If you are doing this today and it is a piece of cake, go ahead and
>> brag;
>> >but I would prefer to hear that caution is well advised, i.e. tales
>> of
>> >misery, shame and corporate disaster resulting from such mistakes.
>> ;-)
>> >
>> >
>> >cheers,
>> >
>> >
>> >
>> >
>> >Jerry Cupples
>> >Interphase Corporation
>> >Dallas, TX USA
>> >http://www.iphase.com
>> >
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