Article : [ART201]

Info : REPONSE 35, le 06/05/2002.

Titre : Solder joint reliability in alternator power diode assemblies, 1999.

Cité dans : [DIV334]  Recherche sur les mots clés power cycling of power device, mai 2002.

Source : Journal of Electronic Materials (Nov. 1999) vol.28, no.11, p.1276-85. 10 refs.
Published : TMS
Price : CCCC 0361-5235/99/$7.00
CODEN : JECMA5
ISSN : 0361-5235
SICI : 0361-5235(199911)28:11L.1276:SJRA;1-5
Conference : InterconnectPACK. Interconnections for Electronic Packaging. San Diego, CA, USA, 28 Feb-4 March 1999
Sponsor(s) : TMS - Miner. Metals & Mater. Soc
Document_Type : Conference Article; Journal
Treatment_Code : Practical; Experimental
Info : Country of Publication : United States
Language : English
Stockage :
Switches : Diodes
Power :
Software :

Abstract :
Power diodes in an alternator convert AC, generated by the spinning
magnetic field, to DC to be used by the battery and all automotive
electrical and electronic components. The diodes are press-fit into Al
heat sinks to quickly and efficiently dissipate heat from the Si dice in
the diode body. The diodes are soldered to a rectifier circuit board by a
wave soldering process using Pb-free eutectic Sn-3.5Ag solder. The set of
positive diodes resides on a different substrate to the set of negative
diodes, resulting in differences in diode lead lengths. The diode body to
solder joint distance on positive diode leads is 7 mm less than that for
negative diodes. Solderability, cross-section micrographs, and
thermal-cycling fatigue reliability were compared for positive and
negative diodes and between diode designs from different suppliers.
Wetting balance tests showed significant solderability differences between
positive and negative diodes and between the two diode designs. Combining
the diode body and lead had a more drastic effect on solderability than
the lead alone. It was discovered that although the nature of diode design
is to dissipate heat quickly and efficiently, there is a large temperature
gradient along the lead immediately above the solder bath, which can be as
much as 100 degrees C just 2 mm from the bath. This large temperature
gradient caused some leads to be too "cold" to form good solder fillets.
The solder fillets obtained in the wetting tests matched those in actual
alternators. Inadequate solder fillets resulted in a 250% difference in
thermal cycling fatigue reliability between the diode designs.

Accession_Number : 2000:6480060 INSPEC

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