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TRA2525

Medium-Current Silicon Rectifiers

ON Semiconductor 

TRA2525 MR3025

Assembly and Soldering Information

There are two basic areas of consideration for successful

implementation of button rectifiers:

1. Mounting and Handling

2. Soldering

Each should be carefully examined before attempting a

finished assembly or mounting operation.

Mounting and Handling

The button rectifier lends itself to a multitude of assembly

arrangements, but one key consideration must always be

included: One Side of the Connections to the Button Must

be Flexible!

This stress relief to the button should also be chosen for

maximum contact area to afford the best heat transfer — but

not at the expense of flexibility. For an annealed copper

terminal a thickness of 0.015″ is suggested.

Strain Relief Terminal

for Button Rectifier

Copper

Terminal

Button

Base

(Heat Sink Material)

The base heat sink may be of various materials whose

shape and size are a function of the individual application

and the heat transfer requirements.

Common

Materials

Steel

Copper

Aluminum

Advantages and Disadvantages

Low Cost: relatively low heat conductivity

High Cost: high heat conductivity

Medium Cost: medium heat conductivity.

Relatively expensive to plate and not all

platers can process aluminum.

Handling of the button during assembly must be relatively

gentle to minimize sharp impact shocks and avoid nicking

of the plastic. Improperly designed automatic handling

equipment is the worst source of unnecessary shocks.

Techniques for vacuum handling and spring loading should

be investigated.

The mechanical stress limits for the button diode are as

follows:

Compression 32 lbs.

142.3 Newton

Tension

32 lbs.

142.3 Newton

Torsion

6–inch lbs. 0.68 Newtons–meters

Shear

55 lbs.

244.7 Newton

MECHANICAL STRESS

COMPRESSION

TORSION

TENSION

SHEAR

Exceeding these recommended maximums can result in

electrical degradation of the device.

Soldering

The button rectifier is basically a semiconductor chip

bonded between two nickel–plated copper heat sinks with an

encapsulating material of epoxy compound. The exposed

metal areas are also tin plated to enhance solderability.

In the soldering process it is important that the

temperature not exceed 260°C if device damage is to be

avoided. Various solder alloys can be used for this operation

but two types are recommended for best results:

1. 95% Sn, 5% Sb; melting point 237°C

2. 96.5% tin, 3.5% silver; melting point 221°C

3. 63% tin, 37% lead; melting point 183°C

Solder is available as preforms or paste. The paste

contains both the metal and flux and can be dispensed

rapidly. The solder preform requires the application of a flux

to assure good wetting of the solder. The type of flux used

depends upon the degree of cleaning to be accomplished and

is a function of the metal involved. These fluxes range from

a mild rosin to a strong acid; e.g., Nickel plating oxides are

best removed by an acid base flux while an activated rosin

flux may be sufficient for tin plated parts.

Since the button is relatively lightweight, there is a

tendency for it to float when the solder becomes liquid. To

prevent bad joints and misalignment, it is suggested that a

weighting or spring loaded fixture be employed. It is also

important that severe thermal shock (either heating or

cooling) be avoided as it may lead to damage of the die or

encapsulant of the part.

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