BU508A Datasheet, PDF (4/6 Pages) Wing Shing Computer Components – NPN TRIPLE DIFFUSED PLANAR SILICON TRANSISTOR(COLOR TV HORIZONTAL OUTPUT APPLICATIONS)

BU508A
TO- 3PN Non Isolated
Precautions for physical handling of Power Plastic Transistors
(TO-126, TO-220 Series, TO-220FP, TO-3P, TO-3PN)
It is a fundamentally accepted fact that a higher junction operating temperature accelerates failure. Circuit designers,
must therefore ensure minimum temperature rise keeping in view Safe Operating Area (SOA) characteristics as well as
suitable mounting on a properly designed heat sink. When mounting power transistors certain precautions must be taken
in operations such as bending of leads, mounting of heat sink, soldering and removal of flux residue. If these operations
are not carried out correctly, the device can be damaged or reliability compromised.
1. Bending and cutting leads
The bending or cutting of the leads requires the following precautions:
1.1 When bending the leads they must be clamped tightly between the
package and the bending point to avoid strain on the package (in particular
in the area where the leads enter the resin). This also applies to cutting the
leads (Fig. 1).
1.2 The leads must be bent at a minimum distance of 3 mm from the package
(Fig. 2a).
1.3 The leads should not be bent at an angle of more than 90° and they must
be bent only once (Fig. 2b).
1.4 The leads must never be bent laterally (Fig. 2c).
1.5 Check that the tool used to cut or form the leads does not damage them
or ruin their surface finish.
2. Mounting on printed circuit
During mounting operations be careful not to apply stress to the power transistor.
2.1 Adhere strictly to the pin spacing of the transistor to avoid forcing the leads.
2.2 Leave a suitable space between printed circuit and transistor; if necessary use a spacer.
2.3 When fixing the device to the printed circuit do not put mechanical stress on the transistor. For this purpose
the device should be soldered to the printed circuit board after the transistor has been fixed to the heat sink
and the heat sink to the printed circuit board.
3. Soldering
In general a transistor should never be exposed to high temperature for any length of time. It is therefore preferable
to use soldering methods where the transistor is exposed to the lowest possible temperatures for a short time.
3.1 Tolerable conditions are 260°C for 10 sec or 350°C for 3 sec. The graphs in fig. 3 give an idea of the excess
junction temperature during the soldering process for a TO-220. It is also important to use suitable fixes for
the tin baths to avoid deterioration of the leads or of the package resin.
3.2 An excess of residual flux between the pins of the transistor or in contact with the resin can reduce the long-
term reliability of the device. The solvent for removing excess fluid must be chosen with care. The use of
solvents derived from
tricholoroethylene is
not recommended on
plastic packages
because the residue
can cause corrosion.
Recommended
solvents are freon or
isopropyl alcohol.
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Data Sheet
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