Surface Mounting Instructions

Rev. V6

Application Note

M538

ADVANCED: Data Sheets contain information regarding a product M/A-COM Technology Solutions

is considering for development. Performance is based on target specifications, simulated results,

and/or prototype measurements. Commitment to develop is not guaranteed.

PRELIMINARY: Data Sheets contain information regarding a product M/A-COM Technology

Solutions has under development. Performance is based on engineering tests. Specifications are

typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available.

Commitment to produce in volume is not guaranteed.

• North America Tel: 800.366.2266 • Europe Tel: +353.21.244.6400

• India Tel: +91.80.43537383

• China Tel: +86.21.2407.1588

Visit www.macomtech.com for additional data sheets and product information.

M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make

changes to the product(s) or information contained herein without notice.

6

Thermal resistance will be a function of the

following:



Thermal conductivity of the substrate or board

material



Footprint size available for heat spreading



Circuit board copper foil weight (2 oz minimum

recommended for power applications)



Via hole quantity and location



Substrate or board thickness



Proximity of additional thermal loads on board



Velocity of air flow (forced air cooling)

Thorough testing of the prototype is the only way to

prove the adequacy of a thermal design.

General Thermal Considerations

A typical solder for a tin-lead soldering process is

Sn63 (63%Sn, 37%Pb), which clearly is the industry

standard for a number of reasons.

Sn63 is a

eutectic compound with a melting point (+183°C)

high enough to exceed the standard operating

temperature limit of most components (+150°C) and

low enough so that internal component materials are

not damaged during proper solder refold. The one

draw back of Sn63 solder when used in combination

with gold plated components is a phenomenon

called “scavenging.” This occurs when gold plating

migrates into the solder joint during reflow, which

may cause embrittlement of the solder joint.

Pretinning the package leads with Sn63 solder paste

with RMA flux reduces the gold concentration and

produces a stronger joint.

A typical solder for a lead-free soldering process is

Tin-Silver-Copper.

95.5Sn-3.8Ag-0.7Cu is one

typical solder alloy composition that can used for a

lead free soldering process.

Solder Selection

General Soldering Precautions

The melting temperature of solder generally

exceeds the recommended maximum operating

temperature of the device. When the entire device

is heated to a high temperature, failure to complete

soldering within a short time could result in device

failure. Therefore, always observe the following

instructions to minimize the thermal stress to the

devices.



Always preheat the device (failure to do so can

cause excessive thermal shock and stress that

can result in damage to the device).



Limit the temperature in the reflow stage to

peak temperature indicated in Tables 1 thru 3.



After completing the soldering process, allow

the devices to cool naturally for at least 3

minutes. Gradual cooling should be used, as

the use of forced cooling will increase the

temperature gradient and may result in latent

failure due to mechanical stress.



Avoid any mechanical stress or shock to the

solder joints and devices during cooling.

A solder stencil is required to apply the optimal

amount of solder paste onto the pads of the

footprint.

The amount and thickness will directly

affect the quality of the joint and are critical to

ensure proper solder connection between the base

of the package and the board. A .004 to .007 inch

thick stainless steel stencil is recommended for most

applications. The stencil opening should be the

Solder Screen Guidelines

Reflow Profile

The most common solder reflow method is

accomplished in a belt furnace using convection

heat transfer. Tables 1 thru 3 along with Figure 1

show a typical convection reflow profile of

temperature versus time. The profile reflects the

three distinct heating stages, or zones (preheat,

reflow, and cooling) recommended in automated

reflow processes to ensure reliable, finished solder

joints.

The profile will vary among soldering

systems and is intended as an example to use as a

starting point.

Other factors that can affect the

profile include the density and types of components

on the board, type of solder used and type of board

or substrate material being used.

Thermocouples should be securely attached to the

top surface of a representative component to

insure the temperature exposure is met. Profile

should be recorded by data acquisition for future

reference.

same size as the footprint PCB pads (1:1

registration), excluding SMOBC areas. However, if

fine pitch components on the same board require a

thinner stencil, aperture modification may be

necessary.