See what’s wrong with PCBs

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The de­sign of a printed cir­cuit board (PCB) can be com­plex, some­times hav­ing more than 2,000 com­po­nents.

What if some­thing is wrong with one of those com­po­nents? How can you de­tect tiny faults in PCB com­po­nents of less than a mil­lime­tre that might cause a fail­ure? Very of­ten ther­mal imag­ing will be the an­swer.

Euro­pean em­bed­ded elec­tron­ics spe­cial­ist 3T has been us­ing ther­mal imag­ing cam­eras for many years through­out its dif­fer­ent ac­tiv­i­ties to de­tect hot spots of less than 125 mi­crons.

“We are us­ing ther­mal imag­ing cam­eras through­out our en­tire process,” says Ron­ald van der Meer, hard­ware engi­neer at the firm.

“When some­thing goes wrong in a PCB, be it im­proper sol­der­ing of a cir­cuit or a fail­ing com­po­nent, the PCB will heat up. There­fore, ther­mal imag­ing is a very good way to di­ag­nose PCB boards in an early stage of a prob­lem. We use it in the de­sign phase of a PCB, to test it be­fore it is sup­plied to the cus­tomer or in the qual­i­fi­ca­tion stage.”

The com­pany re­cently opted for the Flir T420 bench test ther­mal imag­ing cam­era with 50μm close-up lens.

“This close-up lens was ab­so­lutely nec­es­sary, be­cause with­out it the fo­cus dis­tance was too big,” says Van der Meer. “We are deal­ing with mi­cro-elec­tron­ics here at 3T. The mass of the PCB com­po­nents that we need to re­search is so lit­tle, and pos­si­ble tem­per­a­ture changes are so small, that we re­ally need that de­tail.”

The al­ter­na­tive for ther­mal imag­ing in the field of PCB elec­tron­ics is the use of ther­mo­cou­ples, a tem­per­a­ture-mea­sur­ing de­vice con­sist­ing of two wire legs that con­tact each other at one or more spots.

“Although ther­mo­cou­ple mea­sure­ments are still re­quired by cer­tain reg­u­la­tory bod­ies, the prob­lem with ther­mo­cou­ples for mea­sur­ing mi­cro-elec­tron­ics is that these de­vices can ac­tu­ally dis­turb the mea­sure­ment, be­cause they need to make con­tact with the tiny com­po­nents on the PCB board,” says Van der Meer. “Ther­mal imag­ing on the other hand is a non­con­tact tech­nol­ogy, so you don’t have that prob­lem.”

The T420 is a high­per­for­mance ther­mal imag­ing cam­era. It com­bines ex­cel­lent er­gonomics with high image qual­ity of 320 x 240 pix­els. It comes with a tiltable op­ti­cal unit that makes it pos­si­ble to mea­sure, and take im­ages of ob­jects at any an­gle, still in a com­fort­able work­ing po­si­tion.

For 3T, Flir’s Re­searchIR soft­ware for R&D ap­pli­ca­tions was an es­sen­tial part of the ther­mal imag­ing pack­age. Re­searchIR al­lows re­searchers to make high-speed record­ings and per­form ad­vanced ther­mal pat­tern anal­y­sis.

“Some­times we need to cap­ture the pre­cise re­sponse of a one-time ther­mal event,” says Van der Meer. “This would be dif­fi­cult to cap­ture in one still image. That is why the abil­ity to make high-speed video im­ages is crit­i­cal for us.

“Record­ing a cer­tain event helps us to re­con­struct and an­a­lyse the prob­lem more ac­cu­rately. We also im­port our video im­ages ob­tained with Re­ser­achIR into MAT­LAB, a soft­ware pack­age for data visu­al­i­sa­tion, and pro­gram­ming that we use.”

Re­searchIR al­lows the firm’s en­gi­neers to bet­ter an­a­lyse PCB hot spots and find ther­mal peaks. The soft­ware gives users com­plete colouri­sa­tion con­trol, so they can change the colour pal­ette, colour dis­tri­bu­tion, con­trast and isotherms, zoom­ing and pan­ning.

The T400 in­frared cam­era.

The FLIR Re­searchIR soft­ware al­lows re­searchers to make high speed record­ings and per­form ad­vanced ther­mal pat­tern anal­y­sis.

The cur­rent DUT car weighs 175 kg, whereas many com­pet­ing teams are strug­gling to build cars even below 200 kg.

The PCB in­duc­tor is clearly vis­i­ble in the ther­mal image through the PCB’s epoxy layer.

A heated PCB trace.

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