Vicor VI-J00 Family DC-DC Converters and Configurable Power Supplies - Manual (Page 84)

Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
VI-200 and VI-J00 Family Design Guide Rev 3.5 vicorpower.com
Page 83 of 98
Apps. Eng. 800 927.9474 800 735.6200
23. Recommended Soldering Methods,
Tin Lead Pins, and InMate Sockets
The following chapters contain soldering information for
the following Vicor product families; Maxi, Mini, Micro;
VI-200, VI-J00; VI BRICK
® , and similar package filters and
front-ends. This document is intended to provide guidance
in utilizing soldering practices to make high-quality
connections of Vicor power modules to printed circuit
boards. Some care will be taken to outline appropriate
soldering procedures as well as the evaluation of solder
joints in a manner that enables the customer to ensure
that the end application has an optimal connection to the
power module. Common soldering defects will be
examined and direction will be provided for detecting and
handling the common defects.
Vicor’s manufacturing facilities use the IPC-A-610C
standards as a means of establishing quality solder joints.
It is recommended that manufacturing processes using
Vicor modules refer to these same standards, which can
be found, along with supporting documentation, at
www.ipc.org .
ANALYSIS OF A GOOD SOLDER JOINT
The IPC-A-610C standard requires that solder fill at least
75% of the barrel in order to ensure a solid connection.
Ideally, all connections should have a 100% fill. In order to
accomplish this, the solder applied to both the barrel and
the pin must exhibit a process known as wetting. Wetting
occurs when liquid solder on a surface is heated to the
point that it loses a significant amount of latent surface
tension and evenly coats the surface via capillary action
(both cohesion and adhesion).
During the soldering process wetting can be identified by
an even coating of solder on the barrel and pin. In
addition to coating the surface of barrel and pin, the
solder will gather at the intersection of the two and
produce a trailing fillet along each surface. Once wetting
has occurred, then upon solidification it will bond
appropriately to both components, producing a quality
connection. Figure 23–1 shows a side profile of a good
solder joint with a Mini power module. Notice that for
both examples the solder forms a concave meniscus
between pin and barrel. This is an example of a properly
formed fillet and is evidence of good wetting during the
soldering process. The joint between solder and pin as
well as solder and pad should always exhibit a feathered
edge. In Figure 23–1 it can also be seen that the solder
covers a good deal of the surface area of both the pin
and the pad. This is also evidence of good wetting. Notice
also that the solder joint has a smooth surface with a
silver color. This is evidence of good immobilization of the
joint during cooling as well as good cleaning of the board
prior to soldering. All soldering connections should exhibit
similar characteristics regardless of whether they are
soldered by hand or wave soldered.
Figure 23–2 is a top view of the signal and power pin of a
Maxi or Mini module properly soldered to a printed circuit
board. Notice that both the joint and the area around the
joint are clean and free from resin and solder residue. Also
the pad and printed circuit board adjacent to the barrel
are not burnt or discolored and are solidly attached to
each other. In examining a solder joint, be sure that there
is no solder connecting one pad to another. This is known
as a solder bridge and will be discussed further along with
other potential soldering defects.
Figure 23–2 — Maxi / Mini output power pin and Sense pin
Figure 23–1 — Side profile of a Mini module solder joint
OVERVIEW