A P Products Meritec SMT Products Using Lead-Free Solder User Manual

Mounting of

Meritec SMT Products

Using Lead-Free Solder

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com 9/17/04 rev A

Mounting of Meritec SMT Products Using Lead-Free Solder

Contents Page 2
Scope Page 3
Test Samples/Preparation Page 3
Facilities/Equipment Used Page 4
Pb-Free SMT Soldering Profiles Page 5
Summary of Pb-Free SMT Soldering Profiles Page 8

Conclusions Page 9

Commentary Page 10

Backwards Compatibility SMT Profile (Sn63/Pb37) Page 11
Contacting Meritec Page 12

This document © Copyright Meritec 2004

Other Brands and Names Are The Property of Their Respective Owners.

All Statements, Specifications And Technical Information Are Subject To Change At Any Time

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

2

Scope

To determine acceptable methods and materials for mounting Meritec’s SMT products
using lead-free processes. The findings will form the basis by which Meritec can assist it’s
customers in making this crucial changeover.
After reviewing the current product line, it was decided that Meritec’s SOP Sockets
represented the biggest challenge. Of these, we chose to test the TSOP and the PSOP
types as follows:

1...To mount Pb-free Meritec SOP sockets using a Pb-free printed circuit board and
process. Establish maximum, target, and minimum time/temperature profiles from which a
recommendation can be made for Meritec’s customers.

• Maximum time/temperature profile is one that results in a successful wetting and flow of
the solder on the contacts, but begins to show deleterious effects on the plastic of the
socket components.

• Target time/temperature will be the profile that confirms good solder characteristics and
causes no damage to the plastic of the socket.

• Minimum time/temperature profile is one that results in marginal wetting and flow of the
solder alloy on any one contact of the socket. The solder joint will take on characteristics
consistent with what’s known as a “cold” solder joint.

2...Mounting of Pb-free Meritec SOP sockets will also be done using a 63/37 solder alloy
and the currently recommended profile. This will be done to establish a backwards
compatibility of the new plating with a 63/37 lead bearing solder.

Test Samples/Preparation

• Sockets...Two sockets were chosen for inclusion in this test:
Meritec P/N Size/Type

980020-56-P1 56TSOP
980021-44-P1 44PSOP

• Printed Circuit Board...A test Board (Meritec P/N 600440-02) was manufactured with

four pad patterns for each of the two sockets being tested. Further, the pad patterns
were arranged in a way that would maximize infrared “shadowing”. This was done to
emulate a worst case reflow soldering scenario. Immersion silver was chosen as a pcb
finish for the Pb-free tests and Sn63/Pb37 HASL for the backwards compatibility tests.

• Solder Paste...AIM Solder Product Number NC254/SAC305 was used for Pb-free

testing and has an alloy composition of Sn96.5/Ag3.0/Cu0.5 with a no-clean flux
chemistry. Backwards compatibility testing was done using an Indium Corporation of
America Product Number NC-SMQ92J, which is a no-clean Sn63/Pb37 solder paste.

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

3

Facilities

The facilities used for this testing were located at:

APSCO International
3700 Lane Road
Perry, Ohio 44081

APSCO International was chosen for it’s well qualified lead-free SMT and Wave
production lines and knowledgeable personnel. APSCO has been addressing RoHS
compliance since 2003.

Equipment

Equipment used for the Pb free tests was:

Screen Printer...MPM SP
Component Placement...MYDATA MY12
SMT Reflow Oven...Electrovert Omniflo-10
Inspection...Ersa scope
Xray...Nicolet NXR 1510 System

The collection of the time/temperature data was done with a Datapaq Data Logger
and processed using the Datapaq Insight Reflow Tracker v1.40 software.

Additional visual inspection was made using Leica StereoZoom SZ-4
microscopes with 10X eyepieces mounted.

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

4

Pb-Free SMT Soldering Profiles

The profiles collected with the Datapaq hardware and software follow. They are
summarized in a single chart on page 8.

Pb Free “Maximum”

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

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5

Pb Free “Target”

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

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6

Pb Free “Minimum”

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

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Summary of Pb-Free SMT Soldering Profiles

0Min 1Min

250°C

200°C

150°C

100°C

50°C

0°C

2Min

8Min7Min6Min5Min4Min3Min

SOPSocket, Pb Free -High
SOPSocket, Pb Free -Target

SOPSocket, Pb Free - Low

In each case, a Ramp-Soak-Spike (RSS) profile was used.

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

8

Conclusions

Best results were seen in the range of 240°C to 247°C spike temperature with a
minimum time above the liquidus point of the solder. Clearly, profiles such as these are
much more stressful to the plastic components of the SOP sockets. Though the new
lead-free solder alloys do not flow and wet as well as lead-bearing alloys, the solder joints
were quite acceptable based on the new proposed standards. Spike temperatures
below 239°C resulted in unacceptable wetting of the solder to the contacts.

The recommended profile for all Meritec SMT products is the one labeled as “Target” on
page 8. This, when combined with a good SAC solder alloy and flux chemistry should
result in a good starting point.

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

9

Commentary

Other platings, board finishes and solder alloys were considered for inclusion in our tests.
The following is a brief discussion regarding these other materials:

• PCB Finish...Two popular finishes were considered for use in these tests, ENIG

(Electroless Nickel/Immersion Gold) and Immersion Silver. Each has unique benefits and
liabilities that warrant further discussion.

ENIG exhibits better surface wetting of the solder than Immersion Silver, but can suffer
from “black pad” if it’s not cleaned and handled properly during the PCB manufacturing
process. It is felt that as PCB manufacturers modernize their production lines this will
become less of an issue because cleaning equipment is continuously being improved.

Immersion Silver is not prone to “black pad” and is more easily implemented on older
PCB manufacturing lines, because cleaning requirements are not as stringent. This
provides some economic advantage. A liability of Immersion Silver is long term
formation of silver oxides. Though electrically harmless, they are nevertheless esthetically
undesirable.

Because we would be exposing samples mounted on these boards to extreme
environmental conditions in preparation for electrical testing of the “interface” end of the
contact, we needed to eliminate the possibility that no unknown variables would surface.
For this reason, we chose the Immersion Silver board finish over ENIG. It was thought
by many that, by the time of this writing, a lead-free HASL finish may have been
developed and accepted, but it has not.

• Contact Plating...Pure Sn plating of the socket contacts was considered and discarded.

Meritec has taken a conservative approach to pure tin on connector designs with pitches
less than 1mm. There persist, after decades of debate within the industry, uncertainties
regarding tin whisker growth. Our position is that a slight increase in the cost is worth
avoiding the risk of field failures in the future. For this reason, we chose pure Pd as a
contact finish.

• Solder Alloy...There are many solder alloys currently on the market, most of which are

patented. We chose to use the most popular public domain alloy because of it’s wide
availability.

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

10

Backwards Compatibility SMT Profile (Sn63/Pb37)

Realizing that many users will still be soldering with lead-bearing alloys for the foreseeable
future, we’ve included this profile here. The results were very good, demonstrating that
the Pd plating is very compatible with with the older alloys.

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

11

If you require further assistance, please contact Meritec at:

Meritec ®

1359 West Jackson Street

Painesville, Ohio 44077

Phone: [phone] or [phone]

FAX: [phone]

Internet: www.meritec.com

E-mail: [e-mail]

If you would like to contact APSCO to inquire about their services:

APSCO International

3700 Lane Road

Perry, Ohio 44081

Phone: [phone]

FAX: [phone]

Internet: www.apscoinc.com

E-mail: [e-mail]

Meritec • 1359 West Jackson Street • Painesville • Ohio • 44077 • USA

[phone] • [phone] • [phone] FAX • www.meritec.com

12