I am using an 85Pb10Sb5Sn paste with liquidus temp
 of 255 C. As per vendor recommendation plus 30 C at its liquidus.
temp is preferable to ensure good wetability.
I used the paste as die Attach paste for silicon chips.
180 secs duration is the lowest capability of my oven
(Conduction/Convection
type). At this 180 secs time, 30-60 secs is at peak temp of 290 C.
My cool down rate as of the moment is about -6 to -8 C/sec.
What can you say about this cool down rate? Can this affect
an 8 mil silicon chips?





[log in to unmask] on 07/02/2001 09:12:51 AM

To:   "TechNet E-Mail Forum." <[log in to unmask]>, Jonathan A
      Noquil/Cebu/Fairchild@Fairchild
cc:
Subject:  Re: [TN] Cooling Rates



Hi, Jonathan,

Your temperatures seem very high and your 180 C duration is long compared
with what I'm used to using - what sort of boards and what sort of solder
are you using? What components are failing? More details, please.

Have you made sure that the maximum case temperature of any of your
components (especially the failing ones) is not being exceeded?
Have you also made sure that, if any of the components are moisture
sensitive, they are either within their moisture exposure limits or have
been baked out prior to assembly and soldering?
If you're sure everything else is OK and all that you're left with is the
reflow cool-down rate, I would go for about 4 C per minute.

Pete Duncan




                    Jonathan A Noquil
                    <Jonathan.A.Noquil@FAIRCHIL        To:
[log in to unmask]
                    DSEMI.COM>                         cc:     (bcc: DUNCAN
Peter/Asst Prin Engr/ST Aero/ST Group)
                    Sent by: TechNet                   Subject:     Re:
[TN] Cooling Rates
                    <[log in to unmask]>


                    06/28/01 07:40 PM
                    Please respond to "TechNet
                    E-Mail Forum."; Please
                    respond to
                    Jonathan.A.Noquil






Hello Guys,

 What is the best cooling down rate in a reflow oven?
 Does anybody have experience on what maximum cooling down rate
that will not result in Silicon cracking?
We have some silicon cracking (Chips) and we are still evaluating
if fast cool down can cause this problem.
My Profile is:
Pre-heat: 150 C
Soak: 250 C
Reflow 1: 290 C
Reflow 2: 290 C
Time of Reflow: 180 secs

Thank you very much in advance for your ideas tomorrow

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