Solder layer , as the name suggests , is to prevent welding layer. Usually green or other colors , with the cloth covering the layer of copper at the film to insulate it , and to prevent solder adhering to the welding does not require some of the copper . Also protecting the wiring layer to a certain extent . There are certain requirements which the solder resist thickness and hardness , solvent resistance test and adhesion test should meet the standard , the printed circuit board surface no garbage , no extra mark.
1. Types, terms and definitions
1.1 Types
Agents involved in the type of solder processing characteristics divided by technology : Ultraviolet (UV) curable solder resist , heat -curable solder resist , solder resist liquid photosensitive type , dry type solder resist . Excluding solder stripping agent ( ink ) .
1.2 rating
Solder resist is divided into the following three levels for different requirements or optional equipment .
l level : high reliability
PCB solder resist on this level have excellent performance and long life, its high level of inspection and acceptance , the standard is mandatory for continuous operation , do not allow downtime of machinery and equipment .
2 : General Industrial Supplies
The level of the solder resist on the printed circuit board with better performance and longer life , allowing some surface defects are not critical downtime is not required . Suitable for general industrial equipment and facilities, such as computers, communication equipment , senior commercial and general industrial machinery and military equipment and other products.
3 : Consumer Products
Solder resist surface defects on the printed circuit board level is not important , but the function of the entire circuit is required, the low cost of these boards , in its graphics processing available for a limited inspection and testing for television , entertainment activities electronic equipment, toys and non-critical industrial control equipment , or other consumer goods.
1.3 Terms and Definitions
Using GB / T 2036-1994 term "printed circuit term " provisions , and the following terms and definitions.
Blistering Blisters:
Welding operation or during curing , or the solder resist layer due to the air causes the volatile parts of the solder resist layer and the lower substrates bubbling or delamination or peeling of the copper foil produced .
Hydrolytic stability Hydrolytic Stability
Organic or polymer material is exposed to high temperature and high humidity conditions , the state does not change in an irreversible capacity occurs .
Residual solder Webbing
After the soldering operation , the solder adhered to the coating surface.
2. Technical Requirements
2.1 Features before curing
Color and Appearance
Color
The color should be uniform solder resist ( allowing the use of transparent, non- pigment solder resist ) , and in accordance with relevant regulations.
Exterior
UV curing , heat curing , mobility should be consistent type liquid photosensitive solder resist , no crust , sedimentation , gel and other phenomena ; dry -type solder resist thickness should be uniform , no pinholes, bubbles, particles , impurities, layer flow phenomena .
Physical properties
Table 1 Physical properties of the cured product before
The content of harmful substances limits
Table 2 Content of the solder resist harmful substances limits the product
Product Features 2.2 after curing
Exterior
The solder resist layer should be uniform and should not affect the use of the printed board assembly and foreign matter, cracks, inclusions, and off the rough; discoloration of the metal surface should be received after the curing of the solder resist layer, the solder resist layer itself not have a significant discoloration.
Pencil Hardness
Table 3 Various solder pencil hardness after curing
Adhesion
And rigid PCB adhesion
On the surface of the solder resist layer and the substrate metal surface of the cured maximum percentage fall in Table 4 should not exceed a predetermined value.
Table 4 rigid PCB solder resist binding force (comprehensive test board and / or finished board)
And the binding force of the flexible printed circuit board ( PCB solder resist only for flexible requirements )
Separation, cracks or delamination on the flexible printed circuit board substrate , conductive pad surface and cured solder mask should not occur.
Cover vias
When making the PCB has masked vias ( pore diameter ≤ 0.5mm) needs, cover the hole after the implementation of curing , does not allow any one to be masked vias foaming , protrusions, such as cracking caused by bad masked failure.
Adhesion between the layers ( re-coating )
When it is desired in the cured or semi- cured solder resist layer and then cured solder resist layer overlaps the solder resist layer is not separate off.
And marking ink or conformal coating adhesion can ( compatibility )
When the need to cover ( printing ) ink mark on the cured or semi- cured solder mask layer or when conformal coating , ink or marker conformal coating alone can not fall off, and can not be compared on the base cured coating adhesion a significant decrease .
Chemical resistance
Resistance to common chemical properties
Samples of the cured solder resist layer under the experimental test conditions specified in Table 5 , there can not reduce the surface quality (
such as surface roughness , swollen , tacky , foaming or discoloration, etc. ) phenomenon.
Table 5 Resistance to common chemical reagents
Resistant to other chemical reagents
After curing solder mask layer on the metal surface treatment ( HASL , oxidation , chemical nickel plating , chemical tin, silver plating , reflow , wave soldering , etc. ) process, there should be no lower quality surface phenomena , such as surface rough, swelling , sticky, blistering or discoloration.
Hydrolytic stability
After curing solder mask layer at a temperature 97 ℃ ± 2 ℃, relative humidity of 98% under the conditions of placement for 28 days , its status should be no irreversible changes .
Flammability
After curing solder mask layer flame retardant should be consistent with the "UL94-V0" level requirements .
Welding requirements
Weldability
When you press the GB / T 4677-2002 8.2 requirements for welding , soldering solder layer should not affect regional weldability.
Resistance welding
After curing the solder resist according to the provisions of the welding operation , the solder layer should be no blistering , shedding phenomenon, there should be no residual solder on the solder layer .
Electrical performance requirements
Breakdown strength
After curing the solder layer thickness ≥ 0.025mm, its breakdown strength should not be less than the DC voltage 20kV/mm; After curing the solder layer thickness < when 0.025mm, its breakdown strength should not be less than the DC voltage 500V/mm.
Insulation Resistance
After the solder resist layer is cured at normal atmospheric conditions of the test , when the minimum spacing ≥ 0.25mm, the insulation resistance value of the comb- shaped pattern on not less than 500 MΩ (5 × 108Ω).
Insulation resistance after humidification
PCB solder resist coating should be able to withstand the conditions specified in Table 6 without blistering or delamination .
Table 6 humidity level insulation resistance
Electromigration
When Table 7 and GB / T 4677-2002 test specified in 6.4.1, there should be no traces of the electro-migration coated PCB solder layer.
Table 7 electromigration
Temperature cycling
The cured solder mask layer under the test conditions specified in Table 8 should be no blistering, chalking, cracking or delamination.
Table 8 temperature cycling test conditions
Mildew resistance
The cured solder mask should be no support biological growth nutrients or deterioration due to biological growth.
3. Test Methods
3.1 Sample
When you press 6.1.1 A group of tests conducted, the sample is not cured solder resist, when performed by 6.1.2 or 6.2.1 Group B Group C inspection performed, the sample should be in line with 5.1.1 requires standard test panels or finished board with comprehensive test pattern.
Various types of solder resist film thickness after curing shall comply with the corresponding requirements of Table 9, and to ensure that the solder mask and solder enough to withstand voltage 500VDC performance.
Table 9 for all the minimum thickness of the solder resist after curing
Test pattern
Test pattern should be integrated with the solder resist standard sample test pattern is shown in Figure 1.
Coating, imaging and curing of the solder resist
Solder coating should be applied in the application of a sample system, a solder resist according to the manufacturer's recommended coating and curing conditions as the imaging sample or a printed circuit board.
3.2 Test Conditions
Test atmospheric conditions
According to GB/T2421-1999 specified in 4.3, the normal test atmospheric conditions:
Temperature: 15 ℃ ~ 35 ℃
Pressure: 86 kPa ~ 106kPa
Relative humidity: 45% ~ 75%
Recovery Conditions
According to GB/T2421-1999 specified in 4.4, the sample should restore the conditions of Article 5.2.1 of the normal test atmospheric conditions. Unless otherwise specified, the processing conditions of the sample before and after the final test, the sample to be measured under normal atmospheric conditions recovery test, to stabilize. Unless otherwise specified, the recovery time is 1 to 2 hours.
Arbitration Conditions
According to GB/T2421-1999 specified in 4.2, the test standard atmospheric conditions for arbitration:
Temperature: 23 ± 1 ℃
Pressure: 86 kPa ~ 106kPa
Relative humidity: 48% ~ 52%
3.3 Inspection and testing
Unless otherwise specified, inspection and testing should be in the test under normal atmospheric conditions.
Color and Appearance
Prescribed by the GB/T4677-2002, using visual methods or 1.5 to 10 times the magnifying glass to enlarge and intuitive method to detect whether the solder resist 4.1.1.1 and 4.1.1.2 of compliance. 10-fold amplification method to arbitration.
Viscosity and fineness
UV curing, thermal curing type and liquid photosensitive solder resist shall GB 5547-85 and GB / T 6753.1 provisions were detected viscosity and fineness, and determine whether compliance with 4.1.2 of the provisions in Table 1.
Printability
UV curing, thermal curing type liquid photosensitive solder resist and after making serigraphy, application method for detecting 5.3.1 and 4.1.2 to determine whether compliance with the provisions in Table 1.
Dry Size
Dry film type solder resist thickness measurement should be the relevant specification method for determining the width can be measured by ruler, the accuracy should be 1mm, 4.1.2 and determines whether the requirements in Table 1.
The content of harmful substances limits
According to IEC 62321 Ed.1 111/95/CDV requirements for testing, and determine whether compliance with the provisions of Article 4.1.3.
After curing Appearance
After curing conditions stipulated by the relevant norms curing Methods 5.3.1 visual detection cured solder mask meets the provisions of Article 4.2.1.
Pencil Hardness
Pencil hardness of cured solder mask layer should GB / T 6739-2002 requirement to detect and determine whether compliance with the provisions of Article 4.2.2.
Adhesion
And rigid PCB adhesion
Adhesion cured solder mask layer rigid printed board printed by GB / T 9286-1998 requirements for testing, and determine whether compliance with the provisions of Article 4.2.3.1.
And the binding force of the flexible printed circuit board (PCB solder resist only for flexible requirements)
Cured solder bonding layer and flexible printed by flexural fatigue strength test method GB / T 13557-1992 provisions of Chapter 4 of the bending of the flexible printed circuit board 25 cycles (bending diameter should be as 3mm) were detected, and determines whether the requirements of 4.2.3.2.
Cover vias
PDB cured solder masking layer vias should be required to cover at least six vias, according to GB / T 4677-2002 stipulated before and after soldering to detect and determine whether compliance with 4.2. 3.3 requirements.
Adhesion between the layers (re-coating)
Interlayer adhesion of the solder layer cured by GB / T 9286-1998 requirements for testing, and determine whether the provisions of Article 4.2.3.4.
And marking ink or conformal coating adhesion can (compatibility)
Cured solder mask and marking ink or conformal coating adhesion can be detected according to GB / T 9286-1998 requirements and determine whether compliance with the provisions of Article 4.2.3.5.
Chemical resistance
Resistance to common chemical properties
After curing the solder layer samples were soaked in chemicals under the test conditions specified in Table 5, the air suspension set after removing 10min at room temperature., Then 2.0/2.0 corrected visual acuity (without amplification) visual inspection cured solder layer meets the provisions of Article 4.2.4.1.
Resistant to other chemical reagents
After the samples after curing solder mask production recommend using metal surface treatment conditions tested, with 2.0/2.0 corrected visual acuity (without amplification) visual inspection cured solder mask meets the provisions of Article 4.2.4.2.
Hydrolytic stability
Preparation of a saturated aqueous solution of potassium sulfate (per 100ml of distilled water containing about 35g of potassium, 97 ℃ ± 2 ℃) placed in a dryer at a temperature of 97 ℃ ± 2 ℃, the humidity does not exceed 98% of the condition, the vertical sample ceramic plate is placed in a dryer at the top of the solution of potassium (not in contact with each other), the sealing dryer, it is put into a temperature of 97 ℃ ± 2 ℃ test oven for a given time; dry out after application 5.3.1 visual detection methods cured solder mask meets the provisions of Article 4.2.5.
Flammability
The cured solder mask coating material should be required flame retardancy of UL94 is detected and determines whether the solder resist layer requirements 4.2.6.
Welding requirements
Weldability
When you press the GB / T 4677-2002 8.2 requirements for testing, and determine whether the solder layer provisions of Article 4.2.7.1.
Resistance welding
The solder layer samples after curing by GB / T 4677-2002 19c specified in Article 9.2.3 (a tin 260 ℃ ± 5 ℃, 10s, three times) or the provisions of 9.2.6 of 19f (free solder 288 ℃ ± 5 ℃, 10s, three times) requirements for testing, Method 5.3.1 visual detection cured solder mask meets the provisions of Article 4.2.7.2.
Electrical performance requirements
Breakdown strength
According to the thickness of the solder layer after 4677-2002 8.3.2 Measuring curing GB / T, according to the breakdown strength of GB / T 1408 requirements for test specimens, and determine whether the solder layer provisions of Article 4.2.8.1.
Insulation Resistance
GB / T 4677-2002 in accordance with Article 6.4.1 to detect and determine the solder layer meets the requirements of Article 4.2.8.2.
Insulation resistance after humidification
GB / T 4677-2002 in accordance with Article 6.4.1 measured after wet insulation resistance (under test conditions and removed from the chamber at ambient temperature for 1 ~ 2h designate each measuring time), and determines whether the solder layer the provisions of Article 4.2.8.3.
Electromigration
GB / T 4677-2002 in accordance with Article 6.4.1 to detect and determine whether the solder layer provisions of Article 4.2.8.4.
Temperature cycling
According to the provisions of GB / T 2423.22-2002 for testing, and determine whether the requirements of 4.2.9 solder layer bar.
Mildew resistance
By GB/T2423.16-1999 requirements for testing, and determine whether the requirements of the solder layer 4.2.10 bar.
4. Inspection Rules
A group acceptance testing including testing - performance testing before curing and group B testing - performance testing after curing.
A group testing - performance testing before curing
Inspection Lot
A group of test batches of the same batch of the same test raw ingredients under the same conditions in the continuous production of all solder resist, which sample units of barrels or volumes.
A set of test items and Acceptable Quality Level
A set of test items and acceptable quality level AQL (per hundred units nonconforming) in accordance with Table 10.
Table 10 A group of test
Sampling plan
A product should GB/T2828.1 special inspection level S-3 sample; 2,3-level product samples shall be S-2.
Rejected batches
A set of tests if there is a failure and should be rejected. After rigorous testing to reject the transfer rule should GB/T2828.1 degree requirements.
Group B testing - performance testing after curing
Inspection Lot
Inspection lot Group B test is the same as in compliance with the provisions of Article 5.1.1 of the finished PCB processing technology or standard test board with integrated test pattern (see Figure 1) on the press, removed from the test with a qualified group A batch Press coverage of the solder resist, imaging and cured under Article 5.1.2 and PCB solder resist layer to form a group.
Group B test items and Acceptable Quality Level
Group B test items and acceptable quality level AQL (per hundred units nonconforming) in accordance with Table 11.
Table 11 B group test
Sampling plan
A product should GB/T2828.1 special inspection level S-3 sample; 2,3-level product samples shall be S-2. Sampling should be carried out on the production line, if the sample does not meet the requirements of 5.1.1 should be used with a standard test panels integrated test pattern meets the requirements of section 5.1.1, and evenly distributed in the production line, the sample size should be consistent special inspection level S-3 or the provisions of S-2 (depending on the product rating may be).
Rejected batches
If there is a failure in group B test should be rejected. After the rejection of the transfer rules test stringency should GB/T2828.1-2003 Article 4.6.3.
Periodic Inspection
Periodic Inspection Group C test. 6.2.1 The manufacturer shall solder resist a predetermined cycle group C test; When the solder resist changes to the production plant material, formula or process should be timely for the Group C test. Before the test results obtained, should not be affected by group A and group B test product delivery, if the test results do not meet the requirements stated 6.2.1.3 deals.
Group C inspection
Group C test project, the value of the normal production of harmful substances should be carried out every 12 months a test, while changing the material must be tested in a timely manner when the formula or process, the rest of the changes are limited to the materials or workmanship when the recipe tested. Specific requirements are shown in Table 12.
Table 12 C group test
Group C inspection items and Acceptable Quality Level
Group C inspection should have been approved by Group A and Group B test in determining the level of press GB/T2829 Ⅱ random sampling of a sampling plan. RQL substandard quality level should be 40.
Failure
If the group C, there is a performance test samples fail, then the group C test failed.
Substandard treatment
If Group C test failed, the supplier should stop settlement inspection of products, materials and processes and to respond to take improvement measures. After the improvements, the sample should be repeated on a more full performance test for Group C, Group C tests only when all qualified in order to restore to Group A and Group B test.
5. packaging, transport and storage
5.1 Packaging
Solder resist should be opaque containers (such as barrels) packaged and sealed, shall be marked with the manufacturer, trademark, solder resist name, type, color, weight, production date, batch number, expiry date, inspection certificate on its packaging containers and so on.
If after testing, solder resist varieties are dangerous chemicals (such as flammable materials, etc.), should be required to GB190 in Figure 5 indicate the level of related words and logo on the packaging of dangerous goods.
5.2 Transportation
Transit should prevent the sun, rain and avoid heat.
For the case of solder resist dangerous chemicals, transport of dangerous goods according to relevant regulations for product transport.
5.3 Storage
Storage requirements
Solder resist should be stored below 25 ℃ from light and away from heat, isolated from sources of ignition.
Storage life
Solder resist in a sealed packaging and storage conditions specified, the effective storage period is from the date of production of the six months, the solder resist should be used in the storage lifetime.
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