Designing denser PCB with Polyimide ink jet materials

Designing denser PCBs with Polyimide ink Material Jetting

Mate­r­i­al Jet­ting (MJ) is trans­form­ing Addi­tive Man­u­fac­tur­ing (AM) by pro­vid­ing a high-res­o­lu­tion tech­nique for effi­cient­ly deposit­ing mate­r­i­al droplets to cre­ate com­plex struc­tures. This arti­cle dis­cuss­es the cre­ation and syn­the­sis of a state-of-the-art poly­imide pre­cur­sor ink specif­i­cal­ly made for MJ, which makes it pos­si­ble to pro­duce high-per­for­mance poly­imide films. By selec­tive­ly deposit­ing con­duc­tive sil­ver tracks and poly­imide dielec­tric lay­ers, the spe­cial for­mu­la­tion makes it eas­i­er to cre­ate com­pli­cat­ed cir­cuit board designs. This increas­es design free­dom for high-per­for­mance Print­ed Cir­cuit Boards (PCBs) that are more effi­cient and compact.

With this less com­pli­cat­ed method for mak­ing dou­ble-sided PCBs, we can achieve high­er cir­cuit den­si­ties. An insu­lat­ing mate­r­i­al is selec­tive­ly deposit­ed at the cross-over spots, pro­vid­ing an insu­lat­ing bridge for the cir­cuit, as opposed to iso­lat­ing the entire cir­cuit using a dielec­tric plate, com­mon­ly done in dou­ble-sided PCB. Con­trol­ling film topog­ra­phy and remov­ing defects such “cof­fee stain” dry­ing, crack­ing, and delam­i­na­tion are cru­cial when print­ing these local insu­la­tors. As a result, a depend­able insu­la­tor with excep­tion­al film and dielec­tric attrib­ut­es is needed.

Engi­neered poly­mers such as Poly­imide Inks are renowned for their supe­ri­or mechan­i­cal, elec­tri­cal, and chem­i­cal resis­tance as well as their out­stand­ing ther­mal sta­bil­i­ty. The micro­elec­tron­ic indus­try finds this mate­r­i­al espe­cial­ly appeal­ing, as it finds sig­nif­i­cant uses in inter­lay­er dielectrics, pro­tec­tive lay­ers in inte­grat­ed cir­cuit pro­duc­tion, and micro­electro­mechan­i­cal sys­tem (MEMS) devices.

Polyimide Ink Synthesis

The poly­imide pre­cur­sor ink was metic­u­lous­ly craft­ed, com­bin­ing 4,4′-isopropylidenediphenyl‑1,1′-diyldioxy dian­i­line (BAPP), male­ic anhy­dride (MA), and oth­er com­po­nents. This ink demon­strat­ed excel­lent print­abil­i­ty, achiev­ing a print­ing indi­ca­tor Z of 3.98, falling with­in the print­able range. The ink’s for­mu­la­tion allowed for the cre­ation of uni­form and dense poly­imide films through reac­tive MJ, employ­ing a real-time ther­mo-imidi­s­a­tion process.

Effects of Substrate Temperature

The sub­strate tem­per­a­ture dur­ing print­ing played a cru­cial role in deter­min­ing the sur­face mor­phol­o­gy of the print­ed struc­ture. Var­ied sub­strate tem­per­a­tures (120 °C, 150 °C, and 180 °C) were explored in Fig­ure 1, show­cas­ing how high­er tem­per­a­tures led to decreased droplet diam­e­ter but increased thick­ness. This result­ed in improved sur­face qual­i­ty, reduced rough­ness, and sharp­er film edges.

Polyimide Inks: Cross-sectional surface profiling results of droplets deposited on glass by material jetting under substrates temperature of (a) 120 °C, (b) 150 °C, and (c) 180 °C; (d) and their corresponding deposited drop diameters.
Fig­ure 1. Cross-sec­tion­al sur­face pro­fil­ing results of droplets deposit­ed on glass by mate­r­i­al jet­ting under sub­strates tem­per­a­ture of (a) 120 °C, (b) 150 °C, and © 180 °C; (d) and their cor­re­spond­ing deposit­ed drop diameters.

Ther­mal Imidi­s­a­tion Process: The con­ver­sion of the poly­imide pre­cur­sor ink into poly­imide was ini­ti­at­ed through simul­ta­ne­ous sol­vent evap­o­ra­tion and ther­mal imidi­s­a­tion. Fouri­er Trans­form-Infrared Red (FT-IR) spec­troscopy con­firmed the degree of imidi­s­a­tion, with a peak at 1375 cm−1 indi­cat­ing the trans­for­ma­tion. Addi­tion­al post-treat­ment at 180 °C for 15 min­utes sig­nif­i­cant­ly enhanced imidi­s­a­tion con­ver­sion, high­light­ing the impor­tance of con­trolled heating.

Print­ed PI Films as Dielec­tric Insu­la­tors: The dielec­tric con­stant of the print­ed poly­imide film was char­ac­ter­ized, yield­ing a val­ue of 3.41 ± 0.09, com­pa­ra­ble to com­mer­cial poly­imide films. Selec­tive depo­si­tion of poly­imide insu­la­tors onto sil­ver tracks demon­strat­ed the poten­tial for cre­at­ing com­plex cir­cuit board struc­tures. The tech­nique involved print­ing square poly­imide insu­la­tors between crossed sil­ver con­duc­tive tracks, show­cas­ing suc­cess­ful func­tion­al­i­ty and avoid­ing short cir­cuit issues.

A schematic of producing complex circuit board structures by using reactive material jetting technique to co-printing of silver conductive track and polyimide insulator.
Fig­ure 2. A schemat­ic of pro­duc­ing com­plex cir­cuit board struc­tures by using reac­tive mate­r­i­al jet­ting tech­nique to co-print a sil­ver con­duc­tive track and poly­imide insulator.

To demon­strate the capa­bil­i­ty of pro­duc­ing a sin­gle sided cir­cuit board with two over­lapped cir­cuit pat­terns through mate­r­i­al jet­ting, a demon­stra­tor was pro­duced by sub­se­quent­ly print­ing cir­cuit one fol­lowed by poly­imide insu­la­tor deposit­ed on the designed over­lap loca­tions and then cir­cuit pat­tern two (Fig­ure 2). 

This has been a ground­break­ing inkjet print­ing tech­nique for the effi­cient fab­ri­ca­tion of advanced cir­cuit boards. By lever­ag­ing a spe­cial­ly for­mu­lat­ed poly­imide pre­cur­sor ink, it has suc­cess­ful­ly demon­strat­ed the selec­tive depo­si­tion of high-per­for­mance poly­imide insu­la­tors along­side con­duc­tive tracks. This inno­v­a­tive approach presents a con­tin­u­ous process for 3D print­ing com­plex cir­cuits, pro­vid­ing a more ver­sa­tile and cost-effec­tive alter­na­tive to tra­di­tion­al man­u­fac­tur­ing meth­ods which open new pos­si­bil­i­ties for the wide­spread use of func­tion­al poly­mer­ic mate­ri­als in Addi­tive Manufacturing.

We sup­port a wide range of insu­lat­ing poly­imide inks and we can pro­duce new grades after con­sul­ta­tion with our R&D depart­ment. Take the next step toward mate­r­i­al excel­lence and devel­op­ment – reach out to our team today. 

About Darlene Pudolin

Darlene Pudolin is one of CAPLINQ's Application Engineers specializes in Thermal Interface Materials, Fine & Specialty Chemicals, and Soldering Materials within the company's Technical Marketing unit. Darlene recently joined CAPLINQ in early 2023 but has been an experienced materials quality engineer for 5+ years. She has a broad range of experience in materials solution from Thermal Interface Materials, Cement Chemistry, and Hydrogen Renewable Technology. With a long history of serving customers in Industrial and Research academe, Darlene is passionate on driving solutions about troubleshooting points that best fit the market requirements. Based in the Philippines, Darlene holds a Bachelor's degree in Chemical Engineering from Mapua University and currently doing her Master's degree in Energy Engineering at University of the Philippines Diliman.

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