Peter,
All SMT components are normally qualified by the manufacturer for standard
eutectic reflow, based on peak body temperature of 220C or 235C (depending
on size of component). The vast majority of plastic encapsulated components
like PBGAs are also sensitive to a combination of moisture and temperature.
This is why they are shipped to you in dry bags. Once they are removed from
their bags they start to absorb moisture from the ambient air. They must be
reflowed before the critical level of moisture is exceeded which is
identified by their level of sensitivity (level 1 to 6 as identified on the
label on the bag). This level relates to the maximum floor life prior to
reflow at conditions of 30C/60%RH.
Since the level of internal damage is related to a combination of
temperature and moisture, If you increase the reflow temperature this will
have a direct impact on the maximum floor life (it will be reduced). There
have been a number of experiments recently completed to evaluate the impact
of the higher peak body temperatures associated with lead free soldering. It
was clearly demonstrated that increasing this by 30C to 40C will result in
all moisture-sensitive components to be re-classified and downgraded by 2 or
more levels of sensitivity. I can provide you with a list of references if
you are interested.
You may also refer to the joint IPC/JEDEC standard J-STD-033 for more
details (free download at www.jedec.com)
Francois Monette
Cogiscan Inc.
50 De Gaspe, Suite A5
Bromont, Quebec, Canada, J2L 2N8
Tel : (450)534-2644
Fax: (450)534-0092
www.cogiscan.com
------------------------------
Date: Wed, 23 May 2001 17:57:49 +0800
From: "<Peter George Duncan>" <[log in to unmask]>
Subject: Component Failure Temperatures
Morning, All,
I need a quick and general answer to the question "What typically is the
temperture at which components come apart/melt?" My boss asked me how the
use of high melting point (221 deg C) solder would affect components in the
CR Oven, and all I could give him was a fudge answer about thermal profiles
and how even MIL spec devices (rated at 125 deg C) survive 215 deg C+
during soldering with 63/37 solder. Does anyone have an idea of the rough
temperature at which Industrial grade (-40 to +85 deg C) platic-bodied
components fry, and how long it takes to fry them at that temperature?
I had a look through randomly selected component data sheets, but none of
them contained this useful bit of information. They state that if the
maximum case temperature is sustained for an unspecified time, it could
affect the performance and/or reliability of the device, but they advice
was totally non-specific about exactly how much for how long. I experienced
using a component once that had to be manually soldered because it kept
falling apart internally whenever it went near a soldering machine, so I'm
cautious about giving uninformed replies.
I'm trying to solder 35 x 35 mm PBGA's (318 and 388 pins) to an FR4 board
with a finish of 4.5 microinches gold over 150 microinches of Nickel. HMP
solder has been recommended, but the temperature that the boards are
exposed to during soldering goes up by 35 deg C over normal. Your advice,
stories, etc. much appreciated.
Pete Duncan
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