TWI698502B - Method for forming a solder mask layer on a circuit board using double liquid type solder mask ink - Google Patents

Abstract

The present invention discloses a method for forming a solder mask layer on a circuit board. Ink base and hardener of a double liquid type solder mask ink are mixed and coated on a flat sheet carrier to form a solder mask film. The mixed ink are pre-dried before the solder mask film is laminated on a surface of a circuit board. The solder mask layer so formed is provided with extremely high smoothness.

Description

Method for forming solder mask on circuit board by using double-agent solder mask

The invention relates to a manufacturing process of a circuit board, in particular to a method for forming a solder mask on the circuit board.

The surface of the circuit board is generally coated with a solder mask to cover some conductors that do not need to be soldered. Screen printing is a method commonly used to coat the surface of the circuit board with a solder mask. It uses a mesh cloth to coat the solder mask on the surface of the circuit board, and then the solder mask is dried. The solder mask used is usually double Dosage-type solder mask ink includes a main agent and a hardener packaged separately. The main agent and hardener are mixed before coating to prevent the solder mask from cracking or peeling due to excessive hardening of the solder mask.

Before the solder mask ink is applied, the circuit board surface has already formed a circuit, which makes the surface flatness of the solder mask layer formed by subsequent screen printing and drying poor, and its processing error may be as high as ±10 µm, and different parts of the circuit board The thickness of the solder mask may still be different, and the thickness of the solder mask of different circuit boards is often different, and there is a problem of insufficient stability.

In view of this, the main purpose of the present invention is to provide a processing method that can improve the surface flatness of the solder mask.

In order to achieve the above and other objectives, the present invention provides a method for forming a solder mask on a circuit board using a two-component solder mask, which includes:

Mix the main solder mask containing photoimageable solder mask resin, hardener and diluent into a solder mask mixed slurry with a viscosity of 10-200 dPa‧s;

Coating the solder mask mixed slurry on a film-shaped carrier to form a solder mask film;

Drying the solder mask mixed slurry on the solder mask film into a solder mask layer;

Pasting the solder mask on the surface of a circuit board carrying a circuit layer, the solder mask being in contact with the circuit board; and

Remove the film carrier.

Wherein, the film-shaped carrier has a contact surface in contact with the solder resist mixed slurry, and the centerline average roughness (Ra) of the contact surface is 200-600 nm.

The inventor found that by pre-coating the two-component ink on the film carrier, drying it, and then pasting the solder mask on the surface of the circuit board, the flatness of the formed solder mask can be significantly improved, and the processing error can be reduced. Significantly reduced to ±2 µm.

The present invention is characterized in that after the main solder mask and hardener (Hardener) of the double liquid type solder mask ink are mixed into a solder mask mixed paste, they are not applied through screen printing, roller coating or vertical curtains. Coating and other methods are directly applied to the surface of the circuit board, but the solder mask mixture is coated on a film-like carrier with a flat surface to become a solder mask film, and the solder mask film is only layered after the solder mask mixture is pre-dried On the surface of the circuit board, the formed solder mask has extremely high flatness.

The two-component type solder resist ink may be a heat-hardened solder resist ink, a light-hardened solder resist ink or a combination thereof.

Wherein, the main solder mask contains a photoimageable solder resist, which is preferably a carboxyl-containing photoimageable resin, or a combination of epoxy resin and carboxyl-containing photoimageable resin, or other thermal curing Resin, photocurable resin and carboxyl-containing photoimageable resin. For example, the photoimageable solder mask can be a copolymer of an unsaturated carboxylic acid and an unsaturated group-containing compound, or an addition polymer of a carboxyl group-containing diol compound and a diol compound. The acid value of the carboxyl-containing photoimageable resin can be between 20-200 mgKOH/g, and the weight average molecular weight can be between 2000 and 150000.

In addition to photoimageable solder resist, the main solder mask may also contain other additives known in the field of electronic materials, such as organic solvents, antioxidants, fillers, dispersants, colorants, plasticizers, and antistatic agents. , Anti-aging agents, UV absorbers, defoamers, thermal polymerization inhibitors, coupling agents, flame retardants, antifungal agents, flattening agents, tackifiers, release agents, surface modifiers, stabilizers.

For example, the main solder resist agent is the product model PSR-4000 EG23A, PSR-4000 AUS308 or PSR-2000 WT500 sold by Taiwan Sun Ink Co., Ltd. The product model sold is PSR-550RE HR3A or PSR-550D solder resist main agent.

Depending on the thermal curing or light curing characteristics of the two-component solder mask, the aforementioned curing agent may include a photopolymerization agent, a curing aid, a curing catalyst, or a combination thereof. After the main solder mask and the hardener are mixed, the two-component solder mask ink begins to harden; before the two are mixed, the main solder mask and hardener do not undergo a hardening reaction.

The photopolymerization initiator is, for example, a phosphine oxide-based photopolymerization initiator. The hardening auxiliary agent is, for example, a polyfunctional phenolate, polycarboxylic acid and its anhydride, aliphatic or aromatic primary or secondary amine, polyamide resin or isocyanate compound. The hardening catalyst is, for example, an epoxy compound, an oxetane compound, or a combination thereof.

The hardener may also further contain other additives known in the field of electronic materials, such as organic solvents, antioxidants, fillers, dispersants, colorants, plasticizers, antistatic agents, anti-aging agents, ultraviolet absorbers, Antifoaming agent, thermal polymerization inhibitor, coupling agent, flame retardant, antifungal agent, leveling agent, thickener, release agent, surface modifier, stabilizer.

For example, the hardener is, for example, the product model CA-40 AUS308 or CA-40 G24 sold by Taiwan Sun Ink Co., Ltd., or the product model LS-55RE RM- sold by Huying Chemical Industry Co., Ltd. 3 or LS-55D hardener.

After mixing the aforementioned solder resist mixed slurry, a solder resist mixed slurry can be obtained, and the solder resist mixed slurry can be adjusted to an appropriate viscosity by adding a diluent, such as 10-200 dPa‧s, preferably 10-100 dPa ‧S.

The diluent is, for example, dimethylacetamide, methyl ethyl ketone, cyclohexanone, toluene, xylene, tetramethylbenzene, cellosolve, methyl cellosolve, butyl cellosolve, carbitol , Methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, tripropylene glycol monomethyl Ether, ethyl acetate, butyl acetate, butyl lactate, cellulose acetate, butyl cellulose acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetic acid Petroleum solvents such as esters, dipropylene glycol monomethyl ether acetate, propylene carbonate, aliphatic hydrocarbons, petroleum ether, naphtha, coal soluble petroleum spirit, etc., or combinations thereof. After preparing the solder resist mixed slurry, the solder resist mixed slurry is coated on a film-shaped carrier with a flat surface to form a solder resist film. The film carrier has a contact surface in contact with the solder resist mixed slurry, and the centerline average roughness (Ra) of the contact surface is 200-600 nm. The film carrier can be polyethylene terephthalate (PET) or other polyester film, polyimide film, polyimide film, polypropylene film, polystyrene film, etc., and its thickness It is preferably between 10-150 µm. The coating is performed using, for example, a lip coater.

Then, the solder mask is passed through a dryer to dry the solder mask mixed slurry into a solder mask. The thickness of the solder mask can be between 10-200 µm, preferably between 10-50 µm, and the processing error can be controlled within ± 1 µm, the temperature of the dryer is for example 50-150 ℃, depending on the characteristics of the solder mask mixed slurry, the solder mask can also be dried in stages through multiple dryers. The dried solder mask usually has the characteristic of drying to the touch, but it is not completely hardened. The side of the dried solder mask in contact with the film carrier can replicate the average roughness (Ra) of the center line of the contact surface, that is, 200-600 nm.

The solder mask of the dried solder mask film has a surface opposite to the film carrier. To avoid contamination of the surface, a protective film can be laminated on the surface after the solder mask mixed slurry is dried. The protective film It can be polyethylene film, polytetrafluoroethylene film, polypropylene film or surface-treated paper.

Then, the solder mask is laminated on the surface of a circuit board with a circuit layer by using a pressing machine, and the solder mask is in contact with the circuit board. When the solder mask has a protective film, the protective film must be removed before lamination. The solder mask film needs to be laminated on the circuit board surface before the solder mask layer is completely hardened. Preferably, the solder mask film is laminated on the circuit board surface within three days after the solder mask mixture is prepared. In a possible embodiment, after the solder mask of the solder mask is dried, it is directly laminated on the surface of the circuit board without a protective film. In a possible implementation manner, the solder mask is first wound after being coated with a protective film, and then moved to the production line to which the laminator belongs to perform the lamination industry. In a possible implementation manner, after the solder mask is wound up, it is stored at a low temperature for a period of time, and then moved to the production line to which the laminating machine belongs for the laminating industry.

Then, the film-shaped carrier is removed to form a solder mask on the surface of the circuit board, and the solder mask formed by the method disclosed in the present invention has extremely high flatness, and the processing error can be controlled within ±2 µm.

When the solder mask needs to be opened, the solder mask can be further exposed and developed. The exposure can be performed before or after the film carrier is removed. When the exposure operation is before the film carrier is removed During the process, the film carrier is transparent or semi-transparent, and the light irradiated by the exposure operation can pass through the film carrier. Depending on the thermal hardening and/or light hardening characteristics of the solder mask, the circuit board can be baked or irradiated with ultraviolet rays to completely harden the solder mask.

Hereinafter, the characteristics of the present invention are explained through several embodiments.

Example one

Use the product model PSR-2000 WT500 sold by Taiwan Sun Ink Co., Ltd. as the main solder resist agent, and use the product model Ca-25 KX50 sold by Taiwan Sun Ink Co., Ltd. as the hardener, and mix the two Add a suitable amount of diluent to prepare a solder mask mixed slurry, adjust the viscosity to 80 dPa‧s, and then evenly coat the solder mask slurry on a PET film carrier by a lip coater to become a solder mask film, The coating thickness of the mixed slurry is 35 µm, and then the solder mask film is dried step by step through a dryer at a temperature of 70 ℃, 80 ℃, 90 ℃, and 80 ℃, so that the solder resist mixed slurry is dried into a solder mask Then, use a laminator to laminate the dried solder mask on the circuit board with the pre-made circuit, then attach the solder mask to the surface of the circuit board, and finally remove the PET film carrier, the processed circuit The surface of the solder mask of the board is extremely flat, and the machining error is less than ±1 µm.

Example two

Use the product model PSR-550RE HR-3A sold by Huying Chemical Industry Co., Ltd. as the main solder resist agent, and use the product model LS-55RE RM-3 sold by Huying Chemical Industry Co., Ltd. as the hardening agent. After the two are mixed, add an appropriate amount of diluent to prepare a solder mask mixture, adjust the viscosity to 70 dPa‧s, and then apply the solder mask mixture uniformly on a PET film carrier by a lip coater to become a solder mask The coating thickness of the film and the solder mask mixed slurry is 35 µm, and then the solder mask film is dried stepwise through a dryer at a temperature of 80 ℃, 90 ℃, 100 ℃, and 90 ℃ to make the solder mask mixed slurry It is dried into a solder mask, and then the dried solder mask is laminated on a circuit board with a pre-made circuit using a laminator, the solder mask is attached to the surface of the circuit board, and the PET film carrier is finally removed. The surface of the solder mask of the processed circuit board is extremely flat, and the processing error is less than ±1 µm.

Example three

Use the product model PSR-550D sold by Huyin Chemical Industry Co., Ltd. as the main solder resist agent, and use the product model LS-55D sold by Huyin Chemical Industry Co., Ltd. as the hardener, mix the two and add an appropriate amount The thinner is formulated into a solder mask mixture slurry, the viscosity is adjusted to 70 dPa‧s, and then the solder mask mixture slurry is uniformly coated on a PET film carrier by a lip coater to become a solder mask film and solder mask mixture slurry The coating thickness of the material is 35 µm, and then the solder mask film is sequentially dried by a dryer at a temperature of 80 ℃, 90 ℃, 100 ℃, and 90 ℃ to dry the solder mask mixed slurry into a solder mask. Then use a laminating machine to laminate the dried solder mask on the circuit board with the pre-made circuit, the solder mask is attached to the surface of the circuit board, and finally the PET film carrier is removed. The processed circuit board The surface of the solder mask is extremely flat, and the machining error is less than ±1 µm.

Comparative example

Use the product model PSR-2000 WT500 sold by Taiwan Sun Ink Co., Ltd. as the main solder resist agent, and use the product model Ca-25 KX50 sold by Taiwan Sun Ink Co., Ltd. as the hardener, and mix the two Use screen printing to directly coat the surface of the circuit board with pre-made circuits, and use a dryer to dry the solder mask. The surface flatness of the solder mask of the processed circuit board is low, and the processing error is ±10 µm.

It can be seen from Examples 1 to 3 that by pre-coating the two-component ink on the film carrier, drying it, and then pasting the solder mask on the surface of the circuit board, the flatness of the formed solder mask can be significantly improved. The error can be greatly reduced to less than ±2 µm, which is far superior to conventional solder mask ink coating processes that directly apply solder mask ink on circuit boards.

Follow-up process evaluation of solder mask

(1) Die Attach yield (evaluation 1)

Die bonding was performed on the surface of the solder mask layer of the circuit board obtained in the foregoing Example 1, and the die bonding yield was evaluated by the following criteria.

○: The yield exceeds 70%.

△: The yield is between 50-70%.

×: The yield rate is less than 50%.

(2) Bonding strength of Molding Compound (evaluation 2)

The epoxy resin sealant was cured on the surface of the solder mask layer of the circuit board obtained in Example 1, and the cured epoxy resin sealant was removed from the circuit board, and the bonding strength of the sealant was evaluated according to the following criteria.

○: The proportion of the solder mask removed together with the sealant exceeds 90%.

△: The proportion of the solder mask removed along with the sealant is between 60-90%.

×: The ratio of the solder mask removed along with the sealant is less than 60.

It should be noted that during the aforementioned evaluation, there are five types of PET film carriers selected in Example 1:

Evaluation example 1: The centerline average roughness (Ra) of the contact surface of the film-like carrier is 242 nm.

Evaluation example 2: The centerline average roughness (Ra) of the contact surface of the film-like carrier is 276 nm.

Evaluation example 3: The centerline average roughness (Ra) of the contact surface of the film-like carrier is 419 nm.

Evaluation Comparative Example 1: The centerline average roughness (Ra) of the contact surface of the film-like carrier is 121 nm.

Evaluation comparative example 2: The centerline average roughness (Ra) of the contact surface of the film-like carrier is 76 nm.

Table I

As shown in the above description, the present invention uses a film carrier with a contact surface Ra value of 200-600 nm (equivalent to a relatively rough surface of the film carrier contact surface), and a solder mask formed on the circuit board. The die bonding yield and the bonding strength of the sealant are far better than the solder mask formed on the circuit board of the film carrier with the contact surface Ra value below 200 nm (equivalent to the relatively smooth surface of the film carrier contact surface). Therefore, by selecting a film-like carrier with a predetermined Ra value, the solder mask of the circuit board can be given better bonding, and it can be firmly combined with the die and packaging material to be subsequently attached, and exhibit good bonding strength.

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Claims (4)

A method for forming a solder mask on a circuit board using a dual-component solder mask ink includes: Mix the main solder mask containing photoimageable solder mask resin, hardener and diluent into a solder mask mixed slurry with a viscosity of 10-200 dPa‧s; Coating the solder mask mixed slurry on a film-shaped carrier to form a solder mask film; Drying the solder mask mixed slurry on the solder mask film into a solder mask layer; Laminating the solder mask on the surface of a circuit board with a circuit layer, and the solder mask is in contact with the circuit board; and Remove the membrane carrier; Wherein, the film-shaped carrier has a contact surface in contact with the solder resist mixed slurry, and the centerline average roughness (Ra) of the contact surface is 200-600 nm. The method for forming a solder resist layer on a circuit board using a two-component solder resist ink as described in claim 1, wherein the drying temperature of the solder resist mixed slurry is 50-150°C. The method for forming a solder mask on a circuit board using a two-component solder mask as described in claim 1, wherein the thickness of the solder mask is 10-200 µm. The method for forming a solder resist layer on a circuit board using a two-component solder resist ink according to claim 1, wherein the solder resist film further comprises a protective film laminated on the other side of the solder resist layer relative to the film carrier , The protective film is removed before the solder mask is laminated on the circuit board.