High Temperature Electronics PCBs, Soldering & Reliability

Bo b Willis

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Bob Willis Involvement in Lead-Free Process Development Bob Willis has been involved with the introduction and implementation of lead-free process technology for the last seven years. He received A SOLDERTEC/Tin TechnologyGlobal Lead-Free Award for hiscontribution to the industry, helping implementation of the technology. Bob hasbeen a monthl ycontributor to Global S MT magazine for the last si x years. He was responsible for co-ordination and introduction of the First series of hands-on lead-free training workshopsin Europe for Cookson Electronicsduring 1999-2001. These events were run in France, Italy and the UK and involved lead-free theory, hands-on paste prin ting, reflow, wave and hand soldering exercises. Each non commercial event provided the first opportunity for engineers to get first hand experience in the use of lead-free production processesand moneyraised from the e vents waspresented to local charity. More recentlyhe co-ordinated the SMART Group Lead-Free HandsOn Experience at Nepcon Electronics 2003. This gave the opportunity for over 150 engineersto process four different PCB solder finishes, with two different lead-free pastesthrough convection and vapour phase reflow. He also organised Lead-Free Experience 2, 3 + 4 in 2004-2006. He hasalso run training workshopswith research groupslike ITT F, SINTE F, NPL & IVF in Europe. Bob hasorganised and run three lead-free production lines at international exhibitions Productronica, Hanover Fair and Nepcon Electronics in Germanyand England to provide an in sight to the practical u se of lead-free soldering on BGA Ball Grid Array, CSP Chip Scale Package, 0210 chip and through hole intrusive reflow connectors. Thi s resulted in many technical papers being published in Germany, USA and the United Kingdom. Bob also defined the process and assisted with the set-up and running of the first Simultaneous Double Sided Lead-Free Reflow process using tin/sil ver/copper for reflow of through hole and surface mount products. Bob also had the pleasure of contributing a small sect ion to the first Lead-Free Soldering text book “Environment - Friendly Electronics: Lead-Free Technology” written by Jennie Hwang in 2001. The section provided examples of the type of lead-free defects companies may experience in production. Further illustrations of lead-free joints have been featured in here most recent publication “Implementing Lead-Free Electronics” 2005. He hashelped produce bookletson x-rayinspection and lead-free defects with DAGE Industries, Balver Zinn and SMART Group Mr Willis led the SMART Group Lead-Free Mission to Japan and with this team produced a report and organised several conference presentationson their findings. The mission wassupported bythe DTI and visited many companies in Japan as well as presenting a seminar in Tokyo at the Brit ish Embassy to over 60 technologists and senior managers of many of Japans leading producers. Bob was responsible for the Lead-Free Assembly & Soldering "CookBook" CD-ROM concept in 1999, the world’sf irst interactive training resource. He implemented the concept and produced the interactive CD in partnership with the National Physical Laboratory (NPL), drawing on the many resourcesavailable in the industry including valuable workfrom NPL and the DTI. This incorporated manyinterviews with leading engineersinvolved with lead-free research andprocessintroduction; the CD-ROM isnow in its3rd edition.

High Temperature Reports Two FREE Repor ts fr om National Physical Laboratory (NPL) The latest reports from NPL on high temperature materials will be made available during the live event at SMTA International and will also be provided to webinar attendees. The two reports "High Temperature Solder Replacement to Meet RoHS" & "Practical Guide to Soldering PCBs with High Temperature Solder Alloys" cover some of the work undertaken by the engineers at NPL

Technical Reference Books Handbook of High Temperature Superconductor Electronics - Neeraj Khare High Temperature Electronics - M Willander & H Hartnagel High Temperature Electronics - Randy Kirschman High Temperature Electronics - Patrick McCluskey,Thomas Podlesak,Richard Grzybowski Extreme Environment Electronics - John Cressler & H. Alan Mantooth

What solder alloy are you using or considering for High Temperature Assembly?

9% 21%

31%

31% 8%

Sn Tin/Sb Antimon HMP/Pb Lead Sn Tin Sn Tin/Cu Copper Sn Tin/Ag Silver Other

Do you use robotic soldering?

4% 10% 4%

Laser Iron Both None

82%

Component Packaging Product Demonstration Boards Both Analog Devices & TI have produced working demonstrator boards to illustrate their components and operating capability. In both cases using polyimide as a base substrate Plastic parts 175oC Ceramic components 210oC Bare die 210oC Analog Devices

Tex as Instruments

Component Packaging Quartzdyne Inc have been successfully produced board assemblie s for the downhole industry for many years. They have also regula rly published their capability and performance of their products in extreme environments. They have demonstrated reliability improvement as different assembly and desig n technology have been used

SMT product rated at 150oC SMT product rated at 175oC

PTH product rated at 200oC

Hybrid product rated at 200oC Newsletter/Technical paper from 2001

NPL High Temperature Project Assemble polyimide board Selective solder, Robotic Laser & Iron soldering Different solder alloys – HMP, SnSb, SnCu & SnAg High temperature paste and epoxy comparisons Static ageing at 200oC for 1000hr Microsections, optical and x-ray inspection Thermal shock and peel strength measurements Conformal coating performance

My Apology to Suppliers

Boards and connectors do not look in perfect condition after 1000hrs at 200oC

Preferred Four Layer Polyimide 1.6mm Build ½ oz COPPER PLATED TO 1 oz 0.1mm DURAVER P96 SINGLE SIDED CORE

0.038mm 0.100mm

1 x 1080 DURAVER P96 PRE-PREG

0.078mm

1 x 1080 DURAVER P96 PRE-PREG

0.061mm

1 oz COPPER

0.033mm

1.00mm DURAVER P96 CORE

1.000mm

1 oz COPPER

0.033mm

1 x 1080 DURAVER P96 PRE-PREG

0.061mm

1 x 1080 DURAVER P96 PRE-PREG

0.078mm

0.1mm DURAVER P96 SINGLE SIDED CORE ½ oz COPPER PLATED TO 1 oz

0.100mm 0.038mm

The test board was produced f rom four mat erials by Merlin Circuit Technology. The surface finish were all gold over nickel. The peel test boards were produced from one laminate but with three different surface finishes MeteorWave laminate. Nelco N7000 Polyimide Ventec VT901 Polyimide ISOLA P96 Polyimide

Polyimide Test Boards

Standard test and training board design used on many projects. PCB is 1.6mm thick with nickel/gold surface finish. The solder mask used was. The through hole highlighted were used for selective soldering of a high temperature connector. The connectors were rated at 260 oC for soldering but not for continuous high temperature storage at 200 oC. The 1206 chip resistors were used for a separate material test involving shear of the parts from the board All boards were subjected to 500-1000hrs at 200 oC in an air circulated oven

Polyimide Test Boards

One of the important things with through hole sol dering is the lead to hol e ratio, in this case it is based o n the pin size. The finishe d hole size requ ired on the PCB after plating and surface finish es like nickel/go ld wou ld be the pin size plus 0.010” to make manual or automated through hole assembly easy. In this example where the pin is oblong the largest measurement for the pin is across the corners as indicated. The second example above shows the same connector but with square pins

Polyimide Test Boards – Design For Soldering Pad size & shape Standard design rules pin size plus 0.010”

Solder mask opening Standard design rules pad size plus 0.006”

PTH Thermal breaks Reduce number & size of connections to inner pads

Peel Conducted on a DAGE Bond Tester Peel pattern in line with IPC & IEC standards for printed board quality control testing

Tracks being peeled to show possible change in strength after ageing Testing conducted at 0, 500 & 1000hrs at 2000C

Video clip shows the test being conducted

Peel Conducted on a DAGE Bond Tester Peel test r esults for the test boar ds at 0hr Nickel/Gold Solder levelled Silver

5.46N 5.34N 5.33N

Peel test r esults for the test boar ds at 500hr Nickel/Gold 4.12N Solder levelled 4.34N Silver 4.62N Peel test r esults for the test boar ds at 1000hr Nickel/Gold 3.64N Solder levelled 3.85N Silver 3.54N Change in the bond directly under the copper foil

Robotic Soldering Systems Trials boards were processed with the following suppliers, NPL gratefully acknowledges their support and advice for our project Japan UNIX mta Automation ag APOLLO SEIKO Wolf Production Systems GmbH SEICA Spa Other suppliers also supporting the project

Robotic Soldering Extremely flexible Define parameters per joint Different tip designs, point & drag soldering Different laser systems, in process monitoring Cored wire feed Nitrogen support Much improved tip control & temperature control Faster process than selective soldering

Accurate PCB tooling & component lead position

Reference www.wolf-produktionsystems.de

Robotic Soldering

Laser Soldering Laser normally 30-40watts Focus spot size will be the PCB pad size or less Pulse operation capability Long working distance potencial

Robotic Soldering Process Tip soldering

Laser Soldering

Soldering iron tip 2mm Solder iron temperature 385oC Pre solder feed 0.4s Pre heating 0.8s Solder feed 0.4s Solder wire feed speed 75% Solder wire pull back 0.1mm

60w single emitter 940nm M inimum diameter 0.5 – 0.8mm Preheat 0.0s with 0 watt Solder feed 0.6s with 25 watt Hold time 0.2s with 25 watt Solder wire pullback 0.1s Solder wire speed 100%

Automated Laser & Iron Soldering

Reference for our illustration www.wolf-produktionsystems.de

Laser Soldering

Reference for our illustration www.wolf-produktionsystems.de

Robotic Soldering Process

Selective laser soldering

Robotic iron soldering

Any flow line assembly could incorporate preheat of the product prior to soldering Reference www.wolf-produktionsystems.de

Steps in Robotic Iron Soldering

Robotic Soldering Process

Apollo Seiko via HDSA www.hdsa.nl

Steps in Robotic Laser Soldering

Laser Soldering

Laser soldering trials on one of my customer projects, notice the indents on the cored solder wire which are important from a process optimisation point of view and will be cover in more detail

Laser Soldering

Seica Firefly laser soldering system can be configured wit h either top or bottom soldering head. The system at MTC, Coventry is positioned on the bottom. We have run SAC and tin/copper wire and should be able to successfully run other higher temperature alloys

Imported Design File & Alignment

Measurement of the pad, hole and pin size allows the volume of solder required to be defined. Based on the solder core size the solder feed rate is then defined

Pin location , Process Parameters & Profile

Laser Soldering

Laser soldering on Apollo with HMP on test boards

Iron Soldering

Tip soldering on Apollo with tin/antimony Sn95/Sb05

Laser Soldering

mta laser soldering system on test board

Laser Soldering

JapanUnix laser soldering with tin/copper

Iron Soldering

mta iron soldering

Iron Soldering

JapanUnix iron drag soldering with tin/copper

Cored Solder Wire

Examples of cored solder wire reflowing, first the flux flows out of the wire then the solder reflows to wet the surface to be joined. The design of the core can be supplier specific the key feature for automated soldering is no spitting of flux or solder particles. In laser and iron soldering the process is considerably faster

Cored Solder Wire

Flux or solder spitting test with white card. Any evidence of flux or solder residues can be seen on the white surface after wetting the solder iron tip, video from Japan Bonkote

Cored Solder Wire

The impact of solder balls durin g automated solderin g. You can slow down the process to reduce the fast temperature rise times but that impacts assembly times during solderin g. Key feature is selecting material and reducing the percentage flux

Cored Solder Wire

Example of cored wire cross section after feeding through a wire feed system produced by Japan Bonkote

Cored Solder Wire

Wire feeder with indent tool

Wire feed indent tooling

Solderwire feed system used on Apollo Seiko robotic soldering system, the feed systemindents the wire to reduce the possibility of solder balls caused by fast heating of the flux in the cored wire. This may be an advantage on both robotic iron or laser systems

No Indent to the Wire Flux Core

Bob’s simple test reflowing the cored solder wire on a ceramic tile spitting and balls can be seen easily

Indents to the Wire Flux Core

Solder balling is not visible during the tests

Indent to the Wire Flux Core

Solder balling is not visible during the tests

Indents to the Wire Flux Core

Wire is not heated to reflow temperature in this demonstration to show the flux escape from the cored wire

Testing Temperature Rise from  Nitrogen Nitrogen Feed  Hole

Nitrogen Slot

Soldering iron positioned at a known distance from a target disk. The iron is held in place for a known time, and nitrogen flow rate. Surface temperature of the disk is recorded by use of a IR camera system. The target could be produced of any metal and be fixed with a small clamp to the barrel handle of the soldering iron

Testing Temperature Rise from  Nitrogen

Measurements taken on the surface of the board as t he nitrogen flow rate is increased through the soldering iron

Solder Wire Spatter Testing

Calibration or check on the temperature rise based on nitrogen flow can be performed fairly simply. Soldering iron is positioned at a know height above the test board. Test pads on a board have thermocouples mount ed on them. The iron is held above the surface of the board for a known time, fix ed flow rate of nitrogen and iron temperature.

Solder Wire Spatter Testing

Solder spatter or w etting test board could be designed as above with single sided boards with copper OSP or nickel and gold flash finish. One is just a sheet of laminate the second has a bomb site pattern. The soldering iron tip is located a fixed distance from the surface of the board before feeding a know length of wire to the solder tip. Although cheaper to use a sheet of material with out etching the pattern having a targ et gives a reference for counting solder balls and splatter The cross pattern can be used for wetting tests and also to show the impact of nitrogen and temperature on the wetting performance

Solder Wire Spread Testing

Video clip showing JapanUnix robot during a soldering project on copper OSP test samples. Different levels of nitrogen were introduced during tip/solder contact with the copper. It is assumed that the flow rate and purity of the nitrogen would be compared with the degree of flow of the solder. Other variables would be the process parameters, solder alloy and flux used. The same test technique can be used for solder wire spitting tests

Tip Cleaning Options

Sponge cleaner

Brush cleaner

Air jet cleaner

Tip cleaning is more necessary as the temperature of t he alloy and soldering conditions increases. There is a benefit with inert gas at the tip interface during soldering and also when idle

Selective Soldering Trials

Selective soldering trial for tin/silver & lead/tin HMP alloys were conducted on an ACE selective soldering system using flux. Each board provided 100% solder fill of the plated through holes exceeding the minimum requirements of IPC 610 level 3.

Selective Soldering Trials

To run the animated graph you need a player from www.globfx.com/downloads/swfpoint/

Microsections of High Temperature Joints

Selective

Laser

In all but one case the initial intermetallic thickness was equal to or less than 1um with laser or robotic iron soldering processes. The samples that showed a higher intermetallic thickness were produced by HMP alloy. In each case the soldering through hole performance exceeded the IPC 610F specification for level 3

Microsections of High Temperature Joints Average results of the measurements were shown below after 1000hrs, they ranged from 5um to 16um Sample 1 Tin/Antimony Sample 2 Tin/Antimony Sample 3 HMP Sample 4 SAC Sample 5 SAC Sample 6 Tin/Copper/nickel Sample 7 Tin/Copper/nickel

Hand Soldered Selective Soldered Selective Soldered Laser Soldered Robotic Iron Soldered Laser Soldered Robotic Iron Soldered

5um 10.5um 16um 8.5um 8.1um 9.2um 8.4um

Sample test boards with selected solder alloys have been subjected to temperature cycling after soldering between -55 +125 for 1000 plus cycles. The results of this work will be discussed in future NPL presentations

Pull Force Measurements

Copper barrel and solder joint pulled from the test board

Pin and sold er joint surface separation during pull testing

Example image from board 1 sho w through ho le pins w hich have been pu lled from sample b oards after environmental testing. Some samples show separation at the solder to pin interface and others the copper plating to PCB interface. Further analysis is required on the joint pull strength and the difference in intermetallic thickness on the nickel interface of the pins

Pull Force Measurements Slow motion through hole barrel pull out Force (N) 200 150 100 50 0

Slow motion pin pull out from joint

Pull force results were between 185 & 159N for as soldered boards and 148 & 70N for aged boards

Component plating flake

Surface corrosion

Pad Lifting

Termination dissolution

Sulphur corrosion

Solder pin separation

Plating separation

Poor hole fill

PCB delamination

Poor tin wetting

Solder fillet lifting

Copper pad lifting

Solder/fillet tearing

Flux bubbles

Uneven solder fill

Copper barrel pull away

Solder mask damage

Pull out of copper barrel

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