GB2376439A - Improved printing method - Google Patents

Improved printing method Download PDF

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Publication number
GB2376439A
GB2376439A GB0113898A GB0113898A GB2376439A GB 2376439 A GB2376439 A GB 2376439A GB 0113898 A GB0113898 A GB 0113898A GB 0113898 A GB0113898 A GB 0113898A GB 2376439 A GB2376439 A GB 2376439A
Authority
GB
United Kingdom
Prior art keywords
acid
stencil
ester
solder paste
solder
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0113898A
Other versions
GB0113898D0 (en
Inventor
Deborah Mallon
Andrew David Price
Leela Josephine Sequeira
Robert Derek Williams
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fernox Ltd
Original Assignee
Alpha Fry Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alpha Fry Ltd filed Critical Alpha Fry Ltd
Priority to GB0113898A priority Critical patent/GB2376439A/en
Publication of GB0113898D0 publication Critical patent/GB0113898D0/en
Priority to US10/036,952 priority patent/US6936115B2/en
Priority to PCT/GB2002/002045 priority patent/WO2002098598A2/en
Publication of GB2376439A publication Critical patent/GB2376439A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
    • H05K3/1216—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by screen printing or stencil printing
    • H05K3/1233—Methods or means for supplying the conductive material and for forcing it through the screen or stencil
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • B23K35/025—Pastes, creams, slurries
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/12—Using specific substances
    • H05K2203/127—Lubricants, e.g. during drilling of holes
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3485—Applying solder paste, slurry or powder

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)
  • Screen Printers (AREA)

Abstract

A method of printing a solder paste formulation onto a substrate surface through a stencil wherein a lubricant additive is included in the solder paste formulation in order to improve the release of the solder paste from the stencil. The method of the present invention provides an improved release of the solder pastes from a stencil during printing and is therefore of particular use in fine pitch stencil printing.

Description

<Desc/Clms Page number 1>
IMPROVED PRINTING METHOD The present invention relates to an improved printing method and in particular, to a method of fine pitch stencil printing in which a soldering flux vehicle is used which contains an additive to enhance fine pitch stencil printing.
There is a trend in the electronics industry towards the automated manufacture of printed circuit boards (PCBs) and towards the miniaturization of electronic devices with the requirement of finer and finer pitch devices. Solder paste is generally printed onto a substrate through a stainless steel or electroformed stencil. Industry standard stencils for PCB manufacture are generally from 0. 10mm to 0. 150mm in thickness and solder pastes comprising solder powder particles of 25 to 45 microns in diameter are required to print 0. 25mm diameter apertures at a O. 5mm pitch.
Solder paste release from a stainless steel or electroformed stencil and subsequent printed pad definition on a PCB is influenced by the chemical nature of the solder paste and, in particular, the soldering flux vehicle. A solder paste has to have a certain amount of"tack"in order that components can be placed in position on the printed solder paste pads accurately and without loss. However, the tackiness of the solder paste which holds a component in position often prevents good printing of the solder paste onto a substrate through a stencil, i. e. good aperture release of the solder paste on printing may be prevented.
Accordingly, there is a requirement for an improved printing method using a solder paste formulation which has an improved release from a stencil during printing, whilst maintaining the internal tackiness of the solder paste thereby
<Desc/Clms Page number 2>
preventing loss of components during the assembly placement of the components onto the PCB.
Accordingly, the present invention provides a
meLhud of printing a solder paste formulation onto a =-LUJ-iLLU-LCLL--L-Jil substrate surface through a stencil wherein a lubricant additive is included in the solder paste formulation in order to improve the release of the solder paste from the stencil.
The solder paste formulation is generally stencil printed onto the substrate surface using the following steps : (a) placing a stencil over a substrate surface ; (b) printing a solder paste formulation containing a lubricant additive through the stencil; and (c) removing the stencil from the substrate surface.
The stencil is preferably a stainless steel or electroformed stencil which generally has a thickness in the range of from 0. 10mm to 0. 150mm. The stencil used in the method of the present invention will generally have apertures of 0. 20mm and above at a pitch of 0. 40mm and above.
The lubricant additive which is incorporated into the solder pastes used in the method of the present invention is preferably selected from the group consisting of a fatty acid, a fatty alcohol, a fatty acid ester, a fatty alcohol ester, a mineral oil, a wax, a siloxone, a silicone or a micronised polytetrafluoro-ethylene powder.
Particularly preferred lubricant additives for use in the method of the present invention are those comprising a branched chain fatty alcohol or fatty acid, or an ester thereof, wherein the branch point is at the second carbon position. These compounds are generally known as Guerbet alcohols or Guerbet acids.
<Desc/Clms Page number 3>
Specific examples of Guerbet alcohols and Guerbet acids for use in the method of the present invention are 2-butyl-l-octanol, 2-butyl-l-decanol, 2-hexyl-l- octanol, 2-hexyl-l-decanol, 2-hexyl-l-dodecanol, 2octyl-l-dodecanol, 2-decyl-l-tetradecanol, 2butyloctanoic acid, 2-butyldecanoic acid, 2hexyldecanoic acid, 2-hexyldodecanoic acid, 2octyldodecanoic acid, 2-decyltetradecanoic acid or 2hexadecyleicosanoic acid.
The lubricant additive used in the solder paste formulations may be an ester of a fatty alcohol as defined above with a fatty acid, dibasic acid or tribasic acid. Examples are the stearates, oleates, palmitates, isostearates, adipates, trimellitates, thiodipropionates or pentaerythritol esters.
The solder paste compositions used in the method of the present invention will generally comprise from 75% to 95% by weight of solder powder, preferably 85% to 90% by weight of solder powder. The solder powder will generally have an average particle size in the range of from 10 to 80 micrometres, preferably 25 to 45 micrometres.
The solder paste is formed from a suitable alloy composition, for example an SnPb (such as Sn37Pb63), SnPbBi, SnBi, SnPbAg, SnAgCu, SnAgCuBi and SnZnBi.
The vehicle which is used in the compositions which are used in the present invention will generally comprise at least one polar organic solvent such as a polyhydric alcohol including ethylene glycol, diethylene glycol, propylene glycol, sorbitol, pentaerythritol and derivatives thereof, butyl diglyme, dibutyl itaconate, di (propylene glycol) butyl ether, 2-ethyl hexyl diglycol, y-butyrolactone, hexyl carbitol, N-methyl pyrrolidone, N-ethyl pyrrolidone, terpineol or tetraglyme. Tri (propylene glycol) butyl ether is particularly preferred.
The vehicle will generally contain one or more
<Desc/Clms Page number 4>
thickeners which enable the rheological characteristics of the vehicle to be modified, as required. Suitable thickeners include polyacrylic
acid, hydroyenated castor oil and derivatives thereof, polyamides or resins which may be included in an amount of up to 30wt%.
It may be also be necessary for further components to be added to the vehicle to provide, for instance, fluxing activity for solder reflow. Typical fluxing additives which are known to those skilled in the art may be used. Activators may be included in the solder paste compositions in an amount of up to 7wt%. Other additives may include tackifier (s) and/or antioxidants and/or surfactants at a level of less than 5wt%.
The solder pastes which are used in the method of the present invention will generally contain from 0.1 to 2.0% by weight of the lubricant additive.
The advantage of the method of the present invention is that the solder pastes have an improved release from a stencil during printing and thus are adapted for use in fine pitch stencil printing.
The following non-limiting Examples illustrate the present invention.
EXAMPLES 1 TO 18 A number of flux gels were produced from the following components given in Table 1 and then mixed with solder powder (Sn62Pb36Ag2 of 25 to 45 micrometres diameter) to give a solder paste containing 10% flux gel and 90% solder powder.
<Desc/Clms Page number 5>
Ex. No. Comp. 1 2 3 4 5 6 7 8 Components % % % % % 9. % % 0 Rosin 40 35 35 35 35 35 35 35 35 (KE604) TPNB 54 54 54 54 54 54 54 54 54 Styrene 2 2 2 2 2 2 2 2 2 dibromide Thixatrol + 4 4 4 4 4 4 4 4 4 Isocarb 24 5 Isocarb 36 5 Isocarb 5 ester 1605 Kristol T60 5 Paracera MW 5 Isostearic 5 acid Stearic 5 acid Palmitic 5 acid Micronised PTPE 200/lOOcS Dow Corning 704 Isofol 24
<Desc/Clms Page number 6>
Ex. No. 9 10 11 12 13 14 15 16 17 18 Components % % % % % % % % % % Rosin 35 35 35 35 35 35 35 35 35 35 (KE604) TPNB 54 54 54 54 54 54 58 39 58 39 Styrene 2 2 2 2 2 2 2 2 2 2 dibromide Thixatrol + 4 4 4 4 4 4 4 4 4 4 Isocarb 24 2.5 4 1 20 Isocarb 36 Isocarb 2.5 1 1 20 ester 1605 Kristol T60 Paracera MW Iso stearic acid Stearic acid Palmitic acid Micronised 5 PTPE 200/lOOcS 5 Dow Corning 5 704 Isofol 24 5
<Desc/Clms Page number 7>
Footnotes to the Table
Rosin (KE604) Arakawa Acid modified hydrogenated rosin TPNB DOW Tri (Propylene Glycol) Butyl Ether Thixatrol + Rheox Rheological additive Isocarb 24 Condea 2-decyltetradecanoic acid Isocarb 36 Condea 2-hexadecyleicosanoic acid Isocarb ester 1605 Condea 2-hexyldecanoic acid-pentaerythritol ester Kristol T60 Carless Mineral Oil Paracera MW Industrial Paraffin Wax Waxes Ltd Micronised PTPE Ranic Ltd PTFE Micropowder 200/lOOcS Dow Corning Polydimethylsiloxane Dow Corning 704 Dow Corning Tetramethyltetraphenyltrisiloxane and pentaphenyltrimethltrisiloxane Isofol 24 Condea 2-decyltetradecanol
The 1t, 5th and 10th prints were visually examined and compared with a visual standard. In addition the appearance of the first print was recorded at 90 and 45 degrees using the SPIDA (Solder Paste Inspection Data Analyser).
The solder pastes were each printed through a series of 250 micrometre apertures using an electroformed stencil 0.125mm in thickness and an MPM AP27 printer.
The visual standard which was used to assess the print definition on inspection is described with
<Desc/Clms Page number 8>
reference to Figure 1. Referring to Figure 1, T represents the stencil thickness, A the aperture diameter, D the paste diameter and H the paste height.
The following scores were given.
SCORE DESCRIPTION VALUES 1 No paste or almost no paste D < 1/2A H < 1/3T 2 More than of pad area D > 1/2A covered but insufficient H < 2/3T height 3 More than % pad area D > 2/3A covered, paste reaches same H=T for < 1/3A height as stencil 4 More than % pad area D > 2/3A covered and diameter of top H=T for < 1/2A is > 1f3 of aperture 5 Perfect deposit, same shape D = A as stencil aperture H = T for > 2/3A Results The results of the visual inspections are given in Table 2 below.
<Desc/Clms Page number 9>
TABLE 2
Example Additive (%) Score Comparative None 2 1 Isocarb 24 3 2 Isocarb 36 5 3 Isocarb ester 1605 4 4 Kristol T60 4 5 Pancera MW 4 6 Iso stearic acid 4 7 Stearic acid 3 8 Palmitic acid 4 9 Micronised PTFE 3 10 200/lOOcS 3 11 Dow Corning 704 3 12 Isofol 24 4 13 Isocarb 24 (2.5)/Isocarb 4 ester 1605 (2.5) 14 Isocarb 24 (4) /Isocarb 3 ester 1605 (1) 15 Isocarb 24 (1) 3 16 Isocarb 24 (20) 4 17 Isocarb ester 1605 (1) 3 18 Isocarb ester 1605 (20) 3
It can be seen from the results given in Table 2 that the solder pastes made with flux gels containing the lubricant additions showed improved print definition when compared with a paste made with a flux gel containing no lubricant addition.

Claims (16)

CLAIMS :
1. A method of printing a solder paste formulation onto a substrate surface through a stencil wherein a lubricant additive is included in the solder paste formulation in order to improve the release of the solder paste from the stencil.
2. A method as claimed in claim 1 which comprises the steps of (a) placing a stencil over a substrate surface; (b) printing a solder paste formulation containing a lubricant additive through the stencil; and (c) removing the stencil from the substrate surface.
3. A method as claimed in claim 1 or claim 2 wherein the stencil is a stainless steel or electroformed stencil.
4. A method as claimed in any one of the preceding claims wherein the stencil has a thickness of from 0. 10mm to 0. 150mm.
5. A method as claimed in any one of the preceding claims wherein the stencil has apertures of 0. 20mm and above at a pitch of 0. 40mm and above.
6. A method as claimed in any one of the preceding claims wherein the lubricant additive comprises a fatty acid, a fatty alcohol, a fatty acid ester, a fatty alcohol ester, a mineral oil, a wax, a siloxone, a silicone or a micronised polytetrafluoroethylene powder.
<Desc/Clms Page number 11>
7. A method as claimed in claim 6 wherein the lubricant additive is a branched chain fatty alcohol or fatty acid containing a total of from 8 to 50 carbon atoms with a minimum of 4 carbon atoms being present in the shorter alkyl chain, or an ester thereof.
8. A method as claimed in claim 7 wherein the additive is a branched chain fatty alcohol or fatty acid wherein the branch point is at the second carbon position.
9. A method as claimed in claim 7 or claim 8
wherein the additive is 2-butyl-l-octanol, 2-butyl-ldecanol, 2-hexyl-l-octanol, 2-hexyl-l-decanol, 2hexyl-l-dodecanol, 2-octyl-l-dodecanol, 2-decyl-1- tetradecanol, 2-butyloctanoic acid, 2-butyldecanoic acid, 2-hexyldecanoic acid, 2-hexyldodecanoic acid, 2octyldodecanoic acid, 2-decyltetradecanoic acid or 2hexadecyleicosanoic acid.
10. A method as claimed in claim 7 or claim 8 wherein the additive is an ester of a fatty alcohol as defined with a fatty acid, dibasic acid or tribasic acid.
11. A method as claimed in claim 10 wherein the ester is a stearate, oleate, palmitate, isostearate, adipate, trimellitate, thiodipropionate or pentaerythritol ester.
12. A method as claimed in any one of the preceding claims which comprises from 75% to 95% by weight of a solder powder.
13. A method as claimed in claim 12 wherein the solder powder is an alloy composition of SnPb, SnPbBi,
<Desc/Clms Page number 12>
SnBi, SnPbAg, SnAgCu, SnAgCuBi, SnZnBi
14. A method as claimed in claim 12 or claim 13 wherein the solder powder has an average particle size in the range of from 10 to 80 micrometres.
15. A method as claimed in claim 14 wherein the solder powder has an average particle size in the range of from 25 to 45 micrometres.
16. A method as claimed in any one of the preceding claims wherein the solder paste comprises from 0.1 to 2% by weight of the lubricant additive.
GB0113898A 2001-06-07 2001-06-07 Improved printing method Withdrawn GB2376439A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB0113898A GB2376439A (en) 2001-06-07 2001-06-07 Improved printing method
US10/036,952 US6936115B2 (en) 2001-06-07 2001-12-21 Soldering flux vehicle additive and fine pitch printing method
PCT/GB2002/002045 WO2002098598A2 (en) 2001-06-07 2002-05-02 Improved solder printing method

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0113898A GB2376439A (en) 2001-06-07 2001-06-07 Improved printing method

Publications (2)

Publication Number Publication Date
GB0113898D0 GB0113898D0 (en) 2001-08-01
GB2376439A true GB2376439A (en) 2002-12-18

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Family Applications (1)

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GB0113898A Withdrawn GB2376439A (en) 2001-06-07 2001-06-07 Improved printing method

Country Status (2)

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GB (1) GB2376439A (en)
WO (1) WO2002098598A2 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2835213A4 (en) * 2012-04-05 2015-12-09 Senju Metal Industry Co Flux and solder paste

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07132395A (en) * 1993-11-15 1995-05-23 Showa Denko Kk Cream solder
JPH08174265A (en) * 1994-12-27 1996-07-09 Matsushita Electric Ind Co Ltd Cream solder
WO1997003788A1 (en) * 1995-07-20 1997-02-06 Matsushita Electric Industrial Co., Ltd. Cream solder
DE19731151C1 (en) * 1997-07-21 1999-01-21 Degussa Solder paste for brazing and coating of aluminum and aluminum alloys

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2835213A4 (en) * 2012-04-05 2015-12-09 Senju Metal Industry Co Flux and solder paste

Also Published As

Publication number Publication date
WO2002098598A2 (en) 2002-12-12
GB0113898D0 (en) 2001-08-01
WO2002098598A3 (en) 2003-09-25

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