REVISTA ROMÂNĂ DE AUTOMATICĂ - IPA SA

REVISTA ROMÂNĂ DE AUTOMATICĂ
33
DFM Solutions for Tombstoning in Vapour Phase Soldering
Technology based on the CEEX-X2C09 Research Project
I. PLOTOG, N. D. CODREANU, T. C. CUCU
Center for Technological Electronics and Interconnection Techniques (UPB-CETTI),
POLITEHNICA University of Bucharest, Spl. Independentei 313, 060042-Bucharest, Romania,
Phone: +40 21 3169633 E-mail: norocel.codreanu@cetti.ro;
C. TURCU, G. VARZARU
Intrarom S.A, 17 Fabrica de Glucoza St., 020331-Bucharest, Romania,
Phone: +40 21 2040702
Abstract: The physics and chemistry of lead-free reflow soldering process phenomena’s revealed the
inter-dependency between the solder paste, the component, the printed circuit board characteristics and
reflow parameters, especially temperature versus time oven profile, going from the ambient value,
approximately 25ºC, to over melting points, in order to assure liquid status of the solder paste. The paper
presents the applied research performed in order to increase the quality of Lead-Free (LF)
reflow/double-reflow VPS, by ruling out especially tombstoning.
Keywords: VPS, vapour phase technology, lead-free alloy, tombstoning, SMT soldering process
1. Introduction
The goal of this paper is to determine the
general requirements for PCBs and stencils
design when using the „Vapour Phase
Soldering” (VPS) technology in SMT
reflow/double reflow process and to optimize
VPS process parameters. The first
experiments had shown an unacceptably large
number of a specific defect, tombstoning
(figure 1), the partial or complete lifting of
passive SMT components during reflow,
which is the phenomenon whereby small chip
components, which are being soldered on
SMT pads at opposite or polar ends, suddenly
flip up vertically; sometimes the lifting is
partial, and sometimes the chips are staying
on one end like tombstones in a cemetery, on
one of the pads.
a.
b.
Fig. 1a, b. Tombstoning after VPS